Provided by: systemd_256.5-2ubuntu3.1_amd64 bug

NAME

       systemd.exec - Execution environment configuration

SYNOPSIS

       service.service, socket.socket, mount.mount, swap.swap

DESCRIPTION

       Unit configuration files for services, sockets, mount points, and swap devices share a
       subset of configuration options which define the execution environment of spawned
       processes.

       This man page lists the configuration options shared by these four unit types. See
       systemd.unit(5) for the common options of all unit configuration files, and
       systemd.service(5), systemd.socket(5), systemd.swap(5), and systemd.mount(5) for more
       information on the specific unit configuration files. The execution specific configuration
       options are configured in the [Service], [Socket], [Mount], or [Swap] sections, depending
       on the unit type.

       In addition, options which control resources through Linux Control Groups (cgroups) are
       listed in systemd.resource-control(5). Those options complement options listed here.

IMPLICIT DEPENDENCIES

       A few execution parameters result in additional, automatic dependencies to be added:

       •   Units with WorkingDirectory=, RootDirectory=, RootImage=, RuntimeDirectory=,
           StateDirectory=, CacheDirectory=, LogsDirectory= or ConfigurationDirectory= set
           automatically gain dependencies of type Requires= and After= on all mount units
           required to access the specified paths. This is equivalent to having them listed
           explicitly in RequiresMountsFor=.

       •   Similarly, units with PrivateTmp= enabled automatically get mount unit dependencies
           for all mounts required to access /tmp/ and /var/tmp/. They will also gain an
           automatic After= dependency on systemd-tmpfiles-setup.service(8).

       •   Units whose standard output or error output is connected to journal or kmsg (or their
           combinations with console output, see below) automatically acquire dependencies of
           type After= on systemd-journald.socket.

       •   Units using LogNamespace= will automatically gain ordering and requirement
           dependencies on the two socket units associated with systemd-journald@.service
           instances.

PATHS

       The following settings may be used to change a service's view of the filesystem. Please
       note that the paths must be absolute and must not contain a ".."  path component.

       ExecSearchPath=
           Takes a colon separated list of absolute paths relative to which the executable used
           by the Exec*= (e.g.  ExecStart=, ExecStop=, etc.) properties can be found.
           ExecSearchPath= overrides $PATH if $PATH is not supplied by the user through
           Environment=, EnvironmentFile= or PassEnvironment=. Assigning an empty string removes
           previous assignments and setting ExecSearchPath= to a value multiple times will append
           to the previous setting.

           Added in version 250.

       WorkingDirectory=
           Takes a directory path relative to the service's root directory specified by
           RootDirectory=, or the special value "~". Sets the working directory for executed
           processes. If set to "~", the home directory of the user specified in User= is used.
           If not set, defaults to the root directory when systemd is running as a system
           instance and the respective user's home directory if run as user. If the setting is
           prefixed with the "-" character, a missing working directory is not considered fatal.
           If RootDirectory=/RootImage= is not set, then WorkingDirectory= is relative to the
           root of the system running the service manager. Note that setting this parameter might
           result in additional dependencies to be added to the unit (see above).

       RootDirectory=
           Takes a directory path relative to the host's root directory (i.e. the root of the
           system running the service manager). Sets the root directory for executed processes,
           with the pivot_root(2) or chroot(2) system call. If this is used, it must be ensured
           that the process binary and all its auxiliary files are available in the new root.
           Note that setting this parameter might result in additional dependencies to be added
           to the unit (see above).

           The MountAPIVFS= and PrivateUsers= settings are particularly useful in conjunction
           with RootDirectory=. For details, see below.

           If RootDirectory=/RootImage= are used together with NotifyAccess= the notification
           socket is automatically mounted from the host into the root environment, to ensure the
           notification interface can work correctly.

           Note that services using RootDirectory=/RootImage= will not be able to log via the
           syslog or journal protocols to the host logging infrastructure, unless the relevant
           sockets are mounted from the host, specifically:

           The host's os-release(5) file will be made available for the service (read-only) as
           /run/host/os-release. It will be updated automatically on soft reboot (see: systemd-
           soft-reboot.service(8)), in case the service is configured to survive it.

           Example 1. Mounting logging sockets into root environment

               BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout

           In place of the directory path a ".v/" versioned directory may be specified, see
           systemd.v(7) for details.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

       RootImage=
           Takes a path to a block device node or regular file as argument. This call is similar
           to RootDirectory= however mounts a file system hierarchy from a block device node or
           loopback file instead of a directory. The device node or file system image file needs
           to contain a file system without a partition table, or a file system within an
           MBR/MS-DOS or GPT partition table with only a single Linux-compatible partition, or a
           set of file systems within a GPT partition table that follows the Discoverable
           Partitions Specification[1].

           When DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow=
           is set, then this setting adds /dev/loop-control with rw mode, "block-loop" and
           "block-blkext" with rwm mode to DeviceAllow=. See systemd.resource-control(5) for the
           details about DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as it
           may change the setting of DevicePolicy=.

           Units making use of RootImage= automatically gain an After= dependency on
           systemd-udevd.service.

           The host's os-release(5) file will be made available for the service (read-only) as
           /run/host/os-release. It will be updated automatically on soft reboot (see: systemd-
           soft-reboot.service(8)), in case the service is configured to survive it.

           In place of the image path a ".v/" versioned directory may be specified, see
           systemd.v(7) for details.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 233.

       RootImageOptions=
           Takes a comma-separated list of mount options that will be used on disk images
           specified by RootImage=. Optionally a partition name can be prefixed, followed by
           colon, in case the image has multiple partitions, otherwise partition name "root" is
           implied. Options for multiple partitions can be specified in a single line with space
           separators. Assigning an empty string removes previous assignments. Duplicated options
           are ignored. For a list of valid mount options, please refer to mount(8).

           Valid partition names follow the Discoverable Partitions Specification[1]: root, usr,
           home, srv, esp, xbootldr, tmp, var.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 247.

       RootEphemeral=
           Takes a boolean argument. If enabled, executed processes will run in an ephemeral copy
           of the root directory or root image. The ephemeral copy is placed in
           /var/lib/systemd/ephemeral-trees/ while the service is active and is cleaned up when
           the service is stopped or restarted. If RootDirectory= is used and the root directory
           is a subvolume, the ephemeral copy will be created by making a snapshot of the
           subvolume.

           To make sure making ephemeral copies can be made efficiently, the root directory or
           root image should be located on the same filesystem as
           /var/lib/systemd/ephemeral-trees/. When using RootEphemeral= with root directories,
           btrfs(5) should be used as the filesystem and the root directory should ideally be a
           subvolume which systemd can snapshot to make the ephemeral copy. For root images, a
           filesystem with support for reflinks should be used to ensure an efficient ephemeral
           copy.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 254.

       RootHash=
           Takes a data integrity (dm-verity) root hash specified in hexadecimal, or the path to
           a file containing a root hash in ASCII hexadecimal format. This option enables data
           integrity checks using dm-verity, if the used image contains the appropriate integrity
           data (see above) or if RootVerity= is used. The specified hash must match the root
           hash of integrity data, and is usually at least 256 bits (and hence 64 formatted
           hexadecimal characters) long (in case of SHA256 for example). If this option is not
           specified, but the image file carries the "user.verity.roothash" extended file
           attribute (see xattr(7)), then the root hash is read from it, also as formatted
           hexadecimal characters. If the extended file attribute is not found (or is not
           supported by the underlying file system), but a file with the .roothash suffix is
           found next to the image file, bearing otherwise the same name (except if the image has
           the .raw suffix, in which case the root hash file must not have it in its name), the
           root hash is read from it and automatically used, also as formatted hexadecimal
           characters.

           If the disk image contains a separate /usr/ partition it may also be Verity protected,
           in which case the root hash may configured via an extended attribute
           "user.verity.usrhash" or a .usrhash file adjacent to the disk image. There's currently
           no option to configure the root hash for the /usr/ file system via the unit file
           directly.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 246.

       RootHashSignature=
           Takes a PKCS7 signature of the RootHash= option as a path to a DER-encoded signature
           file, or as an ASCII base64 string encoding of a DER-encoded signature prefixed by
           "base64:". The dm-verity volume will only be opened if the signature of the root hash
           is valid and signed by a public key present in the kernel keyring. If this option is
           not specified, but a file with the .roothash.p7s suffix is found next to the image
           file, bearing otherwise the same name (except if the image has the .raw suffix, in
           which case the signature file must not have it in its name), the signature is read
           from it and automatically used.

           If the disk image contains a separate /usr/ partition it may also be Verity protected,
           in which case the signature for the root hash may configured via a .usrhash.p7s file
           adjacent to the disk image. There's currently no option to configure the root hash
           signature for the /usr/ via the unit file directly.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 246.

       RootVerity=
           Takes the path to a data integrity (dm-verity) file. This option enables data
           integrity checks using dm-verity, if RootImage= is used and a root-hash is passed and
           if the used image itself does not contain the integrity data. The integrity data must
           be matched by the root hash. If this option is not specified, but a file with the
           .verity suffix is found next to the image file, bearing otherwise the same name
           (except if the image has the .raw suffix, in which case the verity data file must not
           have it in its name), the verity data is read from it and automatically used.

           This option is supported only for disk images that contain a single file system,
           without an enveloping partition table. Images that contain a GPT partition table
           should instead include both root file system and matching Verity data in the same
           image, implementing the Discoverable Partitions Specification[1].

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 246.

       RootImagePolicy=, MountImagePolicy=, ExtensionImagePolicy=
           Takes an image policy string as per systemd.image-policy(7) to use when mounting the
           disk images (DDI) specified in RootImage=, MountImage=, ExtensionImage=, respectively.
           If not specified the following policy string is the default for RootImagePolicy= and
           MountImagePolicy:

               root=verity+signed+encrypted+unprotected+absent: \
                       usr=verity+signed+encrypted+unprotected+absent: \
                       home=encrypted+unprotected+absent: \
                       srv=encrypted+unprotected+absent: \
                       tmp=encrypted+unprotected+absent: \
                       var=encrypted+unprotected+absent

           The default policy for ExtensionImagePolicy= is:

               root=verity+signed+encrypted+unprotected+absent: \
                       usr=verity+signed+encrypted+unprotected+absent

           Added in version 254.

       MountAPIVFS=
           Takes a boolean argument. If on, a private mount namespace for the unit's processes is
           created and the API file systems /proc/, /sys/, /dev/ and /run/ (as an empty "tmpfs")
           are mounted inside of it, unless they are already mounted. Note that this option has
           no effect unless used in conjunction with RootDirectory=/RootImage= as these four
           mounts are generally mounted in the host anyway, and unless the root directory is
           changed, the private mount namespace will be a 1:1 copy of the host's, and include
           these four mounts. Note that the /dev/ file system of the host is bind mounted if this
           option is used without PrivateDevices=. To run the service with a private, minimal
           version of /dev/, combine this option with PrivateDevices=.

           In order to allow propagating mounts at runtime in a safe manner,
           /run/systemd/propagate/ on the host will be used to set up new mounts, and
           /run/host/incoming/ in the private namespace will be used as an intermediate step to
           store them before being moved to the final mount point.

           Added in version 233.

       ProtectProc=
           Takes one of "noaccess", "invisible", "ptraceable" or "default" (which it defaults
           to). When set, this controls the "hidepid=" mount option of the "procfs" instance for
           the unit that controls which directories with process metainformation (/proc/PID) are
           visible and accessible: when set to "noaccess" the ability to access most of other
           users' process metadata in /proc/ is taken away for processes of the service. When set
           to "invisible" processes owned by other users are hidden from /proc/. If "ptraceable"
           all processes that cannot be ptrace()'ed by a process are hidden to it. If "default"
           no restrictions on /proc/ access or visibility are made. For further details see The
           /proc Filesystem[2]. It is generally recommended to run most system services with this
           option set to "invisible". This option is implemented via file system namespacing, and
           thus cannot be used with services that shall be able to install mount points in the
           host file system hierarchy. Note that the root user is unaffected by this option, so
           to be effective it has to be used together with User= or DynamicUser=yes, and also
           without the "CAP_SYS_PTRACE" capability, which also allows a process to bypass this
           feature. It cannot be used for services that need to access metainformation about
           other users' processes. This option implies MountAPIVFS=.

           If the kernel doesn't support per-mount point hidepid= mount options this setting
           remains without effect, and the unit's processes will be able to access and see other
           process as if the option was not used.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 247.

       ProcSubset=
           Takes one of "all" (the default) and "pid". If "pid", all files and directories not
           directly associated with process management and introspection are made invisible in
           the /proc/ file system configured for the unit's processes. This controls the
           "subset=" mount option of the "procfs" instance for the unit. For further details see
           The /proc Filesystem[2]. Note that Linux exposes various kernel APIs via /proc/, which
           are made unavailable with this setting. Since these APIs are used frequently this
           option is useful only in a few, specific cases, and is not suitable for most
           non-trivial programs.

           Much like ProtectProc= above, this is implemented via file system mount namespacing,
           and hence the same restrictions apply: it is only available to system services, it
           disables mount propagation to the host mount table, and it implies MountAPIVFS=. Also,
           like ProtectProc= this setting is gracefully disabled if the used kernel does not
           support the "subset=" mount option of "procfs".

           Added in version 247.

       BindPaths=, BindReadOnlyPaths=
           Configures unit-specific bind mounts. A bind mount makes a particular file or
           directory available at an additional place in the unit's view of the file system. Any
           bind mounts created with this option are specific to the unit, and are not visible in
           the host's mount table. This option expects a whitespace separated list of bind mount
           definitions. Each definition consists of a colon-separated triple of source path,
           destination path and option string, where the latter two are optional. If only a
           source path is specified the source and destination is taken to be the same. The
           option string may be either "rbind" or "norbind" for configuring a recursive or
           non-recursive bind mount. If the destination path is omitted, the option string must
           be omitted too. Each bind mount definition may be prefixed with "-", in which case it
           will be ignored when its source path does not exist.

           BindPaths= creates regular writable bind mounts (unless the source file system mount
           is already marked read-only), while BindReadOnlyPaths= creates read-only bind mounts.
           These settings may be used more than once, each usage appends to the unit's list of
           bind mounts. If the empty string is assigned to either of these two options the entire
           list of bind mounts defined prior to this is reset. Note that in this case both
           read-only and regular bind mounts are reset, regardless which of the two settings is
           used.

           Using this option implies that a mount namespace is allocated for the unit, i.e. it
           implies the effect of PrivateMounts= (see below).

           This option is particularly useful when RootDirectory=/RootImage= is used. In this
           case the source path refers to a path on the host file system, while the destination
           path refers to a path below the root directory of the unit.

           Note that the destination directory must exist or systemd must be able to create it.
           Thus, it is not possible to use those options for mount points nested underneath paths
           specified in InaccessiblePaths=, or under /home/ and other protected directories if
           ProtectHome=yes is specified.  TemporaryFileSystem= with ":ro" or ProtectHome=tmpfs
           should be used instead.

           Added in version 233.

       MountImages=
           This setting is similar to RootImage= in that it mounts a file system hierarchy from a
           block device node or loopback file, but the destination directory can be specified as
           well as mount options. This option expects a whitespace separated list of mount
           definitions. Each definition consists of a colon-separated tuple of source path and
           destination definitions, optionally followed by another colon and a list of mount
           options.

           Mount options may be defined as a single comma-separated list of options, in which
           case they will be implicitly applied to the root partition on the image, or a series
           of colon-separated tuples of partition name and mount options. Valid partition names
           and mount options are the same as for RootImageOptions= setting described above.

           Each mount definition may be prefixed with "-", in which case it will be ignored when
           its source path does not exist. The source argument is a path to a block device node
           or regular file. If source or destination contain a ":", it needs to be escaped as
           "\:". The device node or file system image file needs to follow the same rules as
           specified for RootImage=. Any mounts created with this option are specific to the
           unit, and are not visible in the host's mount table.

           These settings may be used more than once, each usage appends to the unit's list of
           mount paths. If the empty string is assigned, the entire list of mount paths defined
           prior to this is reset.

           Note that the destination directory must exist or systemd must be able to create it.
           Thus, it is not possible to use those options for mount points nested underneath paths
           specified in InaccessiblePaths=, or under /home/ and other protected directories if
           ProtectHome=yes is specified.

           When DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow=
           is set, then this setting adds /dev/loop-control with rw mode, "block-loop" and
           "block-blkext" with rwm mode to DeviceAllow=. See systemd.resource-control(5) for the
           details about DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as it
           may change the setting of DevicePolicy=.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 247.

       ExtensionImages=
           This setting is similar to MountImages= in that it mounts a file system hierarchy from
           a block device node or loopback file, but instead of providing a destination path, an
           overlay will be set up. This option expects a whitespace separated list of mount
           definitions. Each definition consists of a source path, optionally followed by a colon
           and a list of mount options.

           A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies for sysext
           images and /etc/ hierarchy for confext images. The order in which the images are
           listed will determine the order in which the overlay is laid down: images specified
           first to last will result in overlayfs layers bottom to top.

           Mount options may be defined as a single comma-separated list of options, in which
           case they will be implicitly applied to the root partition on the image, or a series
           of colon-separated tuples of partition name and mount options. Valid partition names
           and mount options are the same as for RootImageOptions= setting described above.

           Each mount definition may be prefixed with "-", in which case it will be ignored when
           its source path does not exist. The source argument is a path to a block device node
           or regular file. If the source path contains a ":", it needs to be escaped as "\:".
           The device node or file system image file needs to follow the same rules as specified
           for RootImage=. Any mounts created with this option are specific to the unit, and are
           not visible in the host's mount table.

           These settings may be used more than once, each usage appends to the unit's list of
           image paths. If the empty string is assigned, the entire list of mount paths defined
           prior to this is reset.

           Each sysext image must carry a /usr/lib/extension-release.d/extension-release.IMAGE
           file while each confext image must carry a
           /etc/extension-release.d/extension-release.IMAGE file, with the appropriate metadata
           which matches RootImage=/RootDirectory= or the host. See: os-release(5). To disable
           the safety check that the extension-release file name matches the image file name, the
           x-systemd.relax-extension-release-check mount option may be appended.

           When DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow=
           is set, then this setting adds /dev/loop-control with rw mode, "block-loop" and
           "block-blkext" with rwm mode to DeviceAllow=. See systemd.resource-control(5) for the
           details about DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as it
           may change the setting of DevicePolicy=.

           In place of the image path a ".v/" versioned directory may be specified, see
           systemd.v(7) for details.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 248.

       ExtensionDirectories=
           This setting is similar to BindReadOnlyPaths= in that it mounts a file system
           hierarchy from a directory, but instead of providing a destination path, an overlay
           will be set up. This option expects a whitespace separated list of source directories.

           A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies for sysext
           images and /etc/ hierarchy for confext images. The order in which the directories are
           listed will determine the order in which the overlay is laid down: directories
           specified first to last will result in overlayfs layers bottom to top.

           Each directory listed in ExtensionDirectories= may be prefixed with "-", in which case
           it will be ignored when its source path does not exist. Any mounts created with this
           option are specific to the unit, and are not visible in the host's mount table.

           These settings may be used more than once, each usage appends to the unit's list of
           directories paths. If the empty string is assigned, the entire list of mount paths
           defined prior to this is reset.

           Each sysext directory must contain a
           /usr/lib/extension-release.d/extension-release.IMAGE file while each confext directory
           must carry a /etc/extension-release.d/extension-release.IMAGE file, with the
           appropriate metadata which matches RootImage=/RootDirectory= or the host. See: os-
           release(5).

           Note that usage from user units requires overlayfs support in unprivileged user
           namespaces, which was first introduced in kernel v5.11.

           In place of the directory path a ".v/" versioned directory may be specified, see
           systemd.v(7) for details.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 251.

USER/GROUP IDENTITY

       These options are only available for system services and are not supported for services
       running in per-user instances of the service manager.

       User=, Group=
           Set the UNIX user or group that the processes are executed as, respectively. Takes a
           single user or group name, or a numeric ID as argument. For system services (services
           run by the system service manager, i.e. managed by PID 1) and for user services of the
           root user (services managed by root's instance of systemd --user), the default is
           "root", but User= may be used to specify a different user. For user services of any
           other user, switching user identity is not permitted, hence the only valid setting is
           the same user the user's service manager is running as. If no group is set, the
           default group of the user is used. This setting does not affect commands whose command
           line is prefixed with "+".

           Note that this enforces only weak restrictions on the user/group name syntax, but will
           generate warnings in many cases where user/group names do not adhere to the following
           rules: the specified name should consist only of the characters a-z, A-Z, 0-9, "_" and
           "-", except for the first character which must be one of a-z, A-Z and "_" (i.e. digits
           and "-" are not permitted as first character). The user/group name must have at least
           one character, and at most 31. These restrictions are made in order to avoid
           ambiguities and to ensure user/group names and unit files remain portable among Linux
           systems. For further details on the names accepted and the names warned about see
           User/Group Name Syntax[3].

           When used in conjunction with DynamicUser= the user/group name specified is
           dynamically allocated at the time the service is started, and released at the time the
           service is stopped — unless it is already allocated statically (see below). If
           DynamicUser= is not used the specified user and group must have been created
           statically in the user database no later than the moment the service is started, for
           example using the sysusers.d(5) facility, which is applied at boot or package install
           time. If the user does not exist by then program invocation will fail.

           If the User= setting is used the supplementary group list is initialized from the
           specified user's default group list, as defined in the system's user and group
           database. Additional groups may be configured through the SupplementaryGroups= setting
           (see below).

       DynamicUser=
           Takes a boolean parameter. If set, a UNIX user and group pair is allocated dynamically
           when the unit is started, and released as soon as it is stopped. The user and group
           will not be added to /etc/passwd or /etc/group, but are managed transiently during
           runtime. The nss-systemd(8) glibc NSS module provides integration of these dynamic
           users/groups into the system's user and group databases. The user and group name to
           use may be configured via User= and Group= (see above). If these options are not used
           and dynamic user/group allocation is enabled for a unit, the name of the dynamic
           user/group is implicitly derived from the unit name. If the unit name without the type
           suffix qualifies as valid user name it is used directly, otherwise a name
           incorporating a hash of it is used. If a statically allocated user or group of the
           configured name already exists, it is used and no dynamic user/group is allocated.
           Note that if User= is specified and the static group with the name exists, then it is
           required that the static user with the name already exists. Similarly, if Group= is
           specified and the static user with the name exists, then it is required that the
           static group with the name already exists. Dynamic users/groups are allocated from the
           UID/GID range 61184...65519. It is recommended to avoid this range for regular system
           or login users. At any point in time each UID/GID from this range is only assigned to
           zero or one dynamically allocated users/groups in use. However, UID/GIDs are recycled
           after a unit is terminated. Care should be taken that any processes running as part of
           a unit for which dynamic users/groups are enabled do not leave files or directories
           owned by these users/groups around, as a different unit might get the same UID/GID
           assigned later on, and thus gain access to these files or directories. If DynamicUser=
           is enabled, RemoveIPC= and PrivateTmp= are implied (and cannot be turned off). This
           ensures that the lifetime of IPC objects and temporary files created by the executed
           processes is bound to the runtime of the service, and hence the lifetime of the
           dynamic user/group. Since /tmp/ and /var/tmp/ are usually the only world-writable
           directories on a system this ensures that a unit making use of dynamic user/group
           allocation cannot leave files around after unit termination. Furthermore
           NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled (and cannot be
           disabled), to ensure that processes invoked cannot take benefit or create SUID/SGID
           files or directories. Moreover ProtectSystem=strict and ProtectHome=read-only are
           implied, thus prohibiting the service to write to arbitrary file system locations. In
           order to allow the service to write to certain directories, they have to be
           allow-listed using ReadWritePaths=, but care must be taken so that UID/GID recycling
           doesn't create security issues involving files created by the service. Use
           RuntimeDirectory= (see below) in order to assign a writable runtime directory to a
           service, owned by the dynamic user/group and removed automatically when the unit is
           terminated. Use StateDirectory=, CacheDirectory= and LogsDirectory= in order to assign
           a set of writable directories for specific purposes to the service in a way that they
           are protected from vulnerabilities due to UID reuse (see below). If this option is
           enabled, care should be taken that the unit's processes do not get access to
           directories outside of these explicitly configured and managed ones. Specifically, do
           not use BindPaths= and be careful with AF_UNIX file descriptor passing for directory
           file descriptors, as this would permit processes to create files or directories owned
           by the dynamic user/group that are not subject to the lifecycle and access guarantees
           of the service. Note that this option is currently incompatible with D-Bus policies,
           thus a service using this option may currently not allocate a D-Bus service name (note
           that this does not affect calling into other D-Bus services). Defaults to off.

           Added in version 232.

       SupplementaryGroups=
           Sets the supplementary Unix groups the processes are executed as. This takes a
           space-separated list of group names or IDs. This option may be specified more than
           once, in which case all listed groups are set as supplementary groups. When the empty
           string is assigned, the list of supplementary groups is reset, and all assignments
           prior to this one will have no effect. In any way, this option does not override, but
           extends the list of supplementary groups configured in the system group database for
           the user. This does not affect commands prefixed with "+".

       SetLoginEnvironment=
           Takes a boolean parameter that controls whether to set the $HOME, $LOGNAME, and $SHELL
           environment variables. If not set, this defaults to true if User=, DynamicUser= or
           PAMName= are set, false otherwise. If set to true, the variables will always be set
           for system services, i.e. even when the default user "root" is used. If set to false,
           the mentioned variables are not set by the service manager, no matter whether User=,
           DynamicUser=, or PAMName= are used or not. This option normally has no effect on
           services of the per-user service manager, since in that case these variables are
           typically inherited from user manager's own environment anyway.

           Added in version 255.

       PAMName=
           Sets the PAM service name to set up a session as. If set, the executed process will be
           registered as a PAM session under the specified service name. This is only useful in
           conjunction with the User= setting, and is otherwise ignored. If not set, no PAM
           session will be opened for the executed processes. See pam(8) for details.

           Note that for each unit making use of this option a PAM session handler process will
           be maintained as part of the unit and stays around as long as the unit is active, to
           ensure that appropriate actions can be taken when the unit and hence the PAM session
           terminates. This process is named "(sd-pam)" and is an immediate child process of the
           unit's main process.

           Note that when this option is used for a unit it is very likely (depending on PAM
           configuration) that the main unit process will be migrated to its own session scope
           unit when it is activated. This process will hence be associated with two units: the
           unit it was originally started from (and for which PAMName= was configured), and the
           session scope unit. Any child processes of that process will however be associated
           with the session scope unit only. This has implications when used in combination with
           NotifyAccess=all, as these child processes will not be able to affect changes in the
           original unit through notification messages. These messages will be considered
           belonging to the session scope unit and not the original unit. It is hence not
           recommended to use PAMName= in combination with NotifyAccess=all.

CAPABILITIES

       These options are only available for system services, or for services running in per-user
       instances of the service manager in which case PrivateUsers= is implicitly enabled
       (requires unprivileged user namespaces support to be enabled in the kernel via the
       "kernel.unprivileged_userns_clone=" sysctl).

       CapabilityBoundingSet=
           Controls which capabilities to include in the capability bounding set for the executed
           process. See capabilities(7) for details. Takes a whitespace-separated list of
           capability names, e.g.  CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities
           listed will be included in the bounding set, all others are removed. If the list of
           capabilities is prefixed with "~", all but the listed capabilities will be included,
           the effect of the assignment inverted. Note that this option also affects the
           respective capabilities in the effective, permitted and inheritable capability sets.
           If this option is not used, the capability bounding set is not modified on process
           execution, hence no limits on the capabilities of the process are enforced. This
           option may appear more than once, in which case the bounding sets are merged by OR, or
           by AND if the lines are prefixed with "~" (see below). If the empty string is assigned
           to this option, the bounding set is reset to the empty capability set, and all prior
           settings have no effect. If set to "~" (without any further argument), the bounding
           set is reset to the full set of available capabilities, also undoing any previous
           settings. This does not affect commands prefixed with "+".

           Use systemd-analyze(1)'s capability command to retrieve a list of capabilities defined
           on the local system.

           Example: if a unit has the following,

               CapabilityBoundingSet=CAP_A CAP_B
               CapabilityBoundingSet=CAP_B CAP_C

           then CAP_A, CAP_B, and CAP_C are set. If the second line is prefixed with "~", e.g.,

               CapabilityBoundingSet=CAP_A CAP_B
               CapabilityBoundingSet=~CAP_B CAP_C

           then, only CAP_A is set.

       AmbientCapabilities=
           Controls which capabilities to include in the ambient capability set for the executed
           process. Takes a whitespace-separated list of capability names, e.g.  CAP_SYS_ADMIN,
           CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. This option may appear more than once, in which case
           the ambient capability sets are merged (see the above examples in
           CapabilityBoundingSet=). If the list of capabilities is prefixed with "~", all but the
           listed capabilities will be included, the effect of the assignment inverted. If the
           empty string is assigned to this option, the ambient capability set is reset to the
           empty capability set, and all prior settings have no effect. If set to "~" (without
           any further argument), the ambient capability set is reset to the full set of
           available capabilities, also undoing any previous settings. Note that adding
           capabilities to the ambient capability set adds them to the process's inherited
           capability set.

           Ambient capability sets are useful if you want to execute a process as a
           non-privileged user but still want to give it some capabilities. Note that in this
           case option keep-caps is automatically added to SecureBits= to retain the capabilities
           over the user change.  AmbientCapabilities= does not affect commands prefixed with
           "+".

           Added in version 229.

SECURITY

       NoNewPrivileges=
           Takes a boolean argument. If true, ensures that the service process and all its
           children can never gain new privileges through execve() (e.g. via setuid or setgid
           bits, or filesystem capabilities). This is the simplest and most effective way to
           ensure that a process and its children can never elevate privileges again. Defaults to
           false. In case the service will be run in a new mount namespace anyway and SELinux is
           disabled, all file systems are mounted with MS_NOSUID flag. Also see No New Privileges
           Flag[4].

           Note that this setting only has an effect on the unit's processes themselves (or any
           processes directly or indirectly forked off them). It has no effect on processes
           potentially invoked on request of them through tools such as at(1), crontab(1),
           systemd-run(1), or arbitrary IPC services.

           Added in version 187.

       SecureBits=
           Controls the secure bits set for the executed process. Takes a space-separated
           combination of options from the following list: keep-caps, keep-caps-locked,
           no-setuid-fixup, no-setuid-fixup-locked, noroot, and noroot-locked. This option may
           appear more than once, in which case the secure bits are ORed. If the empty string is
           assigned to this option, the bits are reset to 0. This does not affect commands
           prefixed with "+". See capabilities(7) for details.

MANDATORY ACCESS CONTROL

       These options are only available for system services and are not supported for services
       running in per-user instances of the service manager.

       SELinuxContext=
           Set the SELinux security context of the executed process. If set, this will override
           the automated domain transition. However, the policy still needs to authorize the
           transition. This directive is ignored if SELinux is disabled. If prefixed by "-",
           failing to set the SELinux security context will be ignored, but it's still possible
           that the subsequent execve() may fail if the policy doesn't allow the transition for
           the non-overridden context. This does not affect commands prefixed with "+". See
           setexeccon(3) for details.

           Added in version 209.

       AppArmorProfile=
           Takes a profile name as argument. The process executed by the unit will switch to this
           profile when started. Profiles must already be loaded in the kernel, or the unit will
           fail. If prefixed by "-", all errors will be ignored. This setting has no effect if
           AppArmor is not enabled. This setting does not affect commands prefixed with "+".

           Added in version 210.

       SmackProcessLabel=
           Takes a SMACK64 security label as argument. The process executed by the unit will be
           started under this label and SMACK will decide whether the process is allowed to run
           or not, based on it. The process will continue to run under the label specified here
           unless the executable has its own SMACK64EXEC label, in which case the process will
           transition to run under that label. When not specified, the label that systemd is
           running under is used. This directive is ignored if SMACK is disabled.

           The value may be prefixed by "-", in which case all errors will be ignored. An empty
           value may be specified to unset previous assignments. This does not affect commands
           prefixed with "+".

           Added in version 218.

PROCESS PROPERTIES

       LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=,
       LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=,
       LimitNICE=, LimitRTPRIO=, LimitRTTIME=
           Set soft and hard limits on various resources for executed processes. See setrlimit(2)
           for details on the process resource limit concept. Process resource limits may be
           specified in two formats: either as single value to set a specific soft and hard limit
           to the same value, or as colon-separated pair soft:hard to set both limits
           individually (e.g.  "LimitAS=4G:16G"). Use the string infinity to configure no limit
           on a specific resource. The multiplicative suffixes K, M, G, T, P and E (to the base
           1024) may be used for resource limits measured in bytes (e.g.  "LimitAS=16G"). For the
           limits referring to time values, the usual time units ms, s, min, h and so on may be
           used (see systemd.time(7) for details). Note that if no time unit is specified for
           LimitCPU= the default unit of seconds is implied, while for LimitRTTIME= the default
           unit of microseconds is implied. Also, note that the effective granularity of the
           limits might influence their enforcement. For example, time limits specified for
           LimitCPU= will be rounded up implicitly to multiples of 1s. For LimitNICE= the value
           may be specified in two syntaxes: if prefixed with "+" or "-", the value is understood
           as regular Linux nice value in the range -20...19. If not prefixed like this the value
           is understood as raw resource limit parameter in the range 0...40 (with 0 being
           equivalent to 1).

           Note that most process resource limits configured with these options are per-process,
           and processes may fork in order to acquire a new set of resources that are accounted
           independently of the original process, and may thus escape limits set. Also note that
           LimitRSS= is not implemented on Linux, and setting it has no effect. Often it is
           advisable to prefer the resource controls listed in systemd.resource-control(5) over
           these per-process limits, as they apply to services as a whole, may be altered
           dynamically at runtime, and are generally more expressive. For example, MemoryMax= is
           a more powerful (and working) replacement for LimitRSS=.

           Note that LimitNPROC= will limit the number of processes from one (real) UID and not
           the number of processes started (forked) by the service. Therefore the limit is
           cumulative for all processes running under the same UID. Please also note that the
           LimitNPROC= will not be enforced if the service is running as root (and not dropping
           privileges). Due to these limitations, TasksMax= (see systemd.resource-control(5)) is
           typically a better choice than LimitNPROC=.

           Resource limits not configured explicitly for a unit default to the value configured
           in the various DefaultLimitCPU=, DefaultLimitFSIZE=, ... options available in systemd-
           system.conf(5), and – if not configured there – the kernel or per-user defaults, as
           defined by the OS (the latter only for user services, see below).

           For system units these resource limits may be chosen freely. When these settings are
           configured in a user service (i.e. a service run by the per-user instance of the
           service manager) they cannot be used to raise the limits above those set for the user
           manager itself when it was first invoked, as the user's service manager generally
           lacks the privileges to do so. In user context these configuration options are hence
           only useful to lower the limits passed in or to raise the soft limit to the maximum of
           the hard limit as configured for the user. To raise the user's limits further, the
           available configuration mechanisms differ between operating systems, but typically
           require privileges. In most cases it is possible to configure higher per-user resource
           limits via PAM or by setting limits on the system service encapsulating the user's
           service manager, i.e. the user's instance of user@.service. After making such changes,
           make sure to restart the user's service manager.

           Table 1. Resource limit directives, their equivalent ulimit shell commands and the
           unit used
           ┌─────────────────┬───────────────────┬─────────────────────┬─────────────────────┐
           │Directiveulimit equivalent │ UnitNotes               │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitCPU=        │ ulimit -t         │ Seconds             │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitFSIZE=      │ ulimit -f         │ Bytes               │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitDATA=       │ ulimit -d         │ Bytes               │ Don't use. This     │
           │                 │                   │                     │ limits the allowed  │
           │                 │                   │                     │ address range, not  │
           │                 │                   │                     │ memory use!         │
           │                 │                   │                     │ Defaults to         │
           │                 │                   │                     │ unlimited and       │
           │                 │                   │                     │ should not be       │
           │                 │                   │                     │ lowered. To limit   │
           │                 │                   │                     │ memory use, see     │
           │                 │                   │                     │ MemoryMax= in       │
           │                 │                   │                     │ systemd.resource-   │
           │                 │                   │                     │ control(5).         │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitSTACK=      │ ulimit -s         │ Bytes               │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitCORE=       │ ulimit -c         │ Bytes               │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitRSS=        │ ulimit -m         │ Bytes               │ Don't use. No       │
           │                 │                   │                     │ effect on Linux.    │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitNOFILE=     │ ulimit -n         │ Number of File      │ Don't use. Be       │
           │                 │                   │ Descriptors         │ careful when        │
           │                 │                   │                     │ raising the soft    │
           │                 │                   │                     │ limit above 1024,   │
           │                 │                   │                     │ since select(2)     │
           │                 │                   │                     │ cannot function     │
           │                 │                   │                     │ with file           │
           │                 │                   │                     │ descriptors above   │
           │                 │                   │                     │ 1023 on Linux.      │
           │                 │                   │                     │ Nowadays, the hard  │
           │                 │                   │                     │ limit defaults to   │
           │                 │                   │                     │ 524288, a very high │
           │                 │                   │                     │ value compared to   │
           │                 │                   │                     │ historical          │
           │                 │                   │                     │ defaults. Typically │
           │                 │                   │                     │ applications should │
           │                 │                   │                     │ increase their soft │
           │                 │                   │                     │ limit to the hard   │
           │                 │                   │                     │ limit on their own, │
           │                 │                   │                     │ if they are OK with │
           │                 │                   │                     │ working with file   │
           │                 │                   │                     │ descriptors above   │
           │                 │                   │                     │ 1023, i.e. do not   │
           │                 │                   │                     │ use select(2). Note │
           │                 │                   │                     │ that file           │
           │                 │                   │                     │ descriptors are     │
           │                 │                   │                     │ nowadays accounted  │
           │                 │                   │                     │ like any other form │
           │                 │                   │                     │ of memory, thus     │
           │                 │                   │                     │ there should not be │
           │                 │                   │                     │ any need to lower   │
           │                 │                   │                     │ the hard limit. Use │
           │                 │                   │                     │ MemoryMax= to       │
           │                 │                   │                     │ control overall     │
           │                 │                   │                     │ service memory use, │
           │                 │                   │                     │ including file      │
           │                 │                   │                     │ descriptor memory.  │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitAS=         │ ulimit -v         │ Bytes               │ Don't use. This     │
           │                 │                   │                     │ limits the allowed  │
           │                 │                   │                     │ address range, not  │
           │                 │                   │                     │ memory use!         │
           │                 │                   │                     │ Defaults to         │
           │                 │                   │                     │ unlimited and       │
           │                 │                   │                     │ should not be       │
           │                 │                   │                     │ lowered. To limit   │
           │                 │                   │                     │ memory use, see     │
           │                 │                   │                     │ MemoryMax= in       │
           │                 │                   │                     │ systemd.resource-   │
           │                 │                   │                     │ control(5).         │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitNPROC=      │ ulimit -u         │ Number of Processes │ This limit is       │
           │                 │                   │                     │ enforced based on   │
           │                 │                   │                     │ the number of       │
           │                 │                   │                     │ processes belonging │
           │                 │                   │                     │ to the user.        │
           │                 │                   │                     │ Typically it's      │
           │                 │                   │                     │ better to track     │
           │                 │                   │                     │ processes per       │
           │                 │                   │                     │ service, i.e. use   │
           │                 │                   │                     │ TasksMax=, see      │
           │                 │                   │                     │ systemd.resource-   │
           │                 │                   │                     │ control(5).         │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitMEMLOCK=    │ ulimit -l         │ Bytes               │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitLOCKS=      │ ulimit -x         │ Number of Locks     │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitSIGPENDING= │ ulimit -i         │ Number of Queued    │ -                   │
           │                 │                   │ Signals             │                     │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitMSGQUEUE=   │ ulimit -q         │ Bytes               │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitNICE=       │ ulimit -e         │ Nice Level          │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitRTPRIO=     │ ulimit -r         │ Realtime Priority   │ -                   │
           ├─────────────────┼───────────────────┼─────────────────────┼─────────────────────┤
           │LimitRTTIME=     │ ulimit -R         │ Microseconds        │ -                   │
           └─────────────────┴───────────────────┴─────────────────────┴─────────────────────┘

       UMask=
           Controls the file mode creation mask. Takes an access mode in octal notation. See
           umask(2) for details. Defaults to 0022 for system units. For user units the default
           value is inherited from the per-user service manager (whose default is in turn
           inherited from the system service manager, and thus typically also is 0022 — unless
           overridden by a PAM module). In order to change the per-user mask for all user
           services, consider setting the UMask= setting of the user's user@.service system
           service instance. The per-user umask may also be set via the umask field of a user's
           JSON User Record[5] (for users managed by systemd-homed.service(8) this field may be
           controlled via homectl --umask=). It may also be set via a PAM module, such as
           pam_umask(8).

       CoredumpFilter=
           Controls which types of memory mappings will be saved if the process dumps core (using
           the /proc/pid/coredump_filter file). Takes a whitespace-separated combination of
           mapping type names or numbers (with the default base 16). Mapping type names are
           private-anonymous, shared-anonymous, private-file-backed, shared-file-backed,
           elf-headers, private-huge, shared-huge, private-dax, shared-dax, and the special
           values all (all types) and default (the kernel default of "private-anonymous
           shared-anonymous elf-headers private-huge"). See core(5) for the meaning of the
           mapping types. When specified multiple times, all specified masks are ORed. When not
           set, or if the empty value is assigned, the inherited value is not changed.

           Example 2. Add DAX pages to the dump filter

               CoredumpFilter=default private-dax shared-dax

           Added in version 246.

       KeyringMode=
           Controls how the kernel session keyring is set up for the service (see session-
           keyring(7) for details on the session keyring). Takes one of inherit, private, shared.
           If set to inherit no special keyring setup is done, and the kernel's default behaviour
           is applied. If private is used a new session keyring is allocated when a service
           process is invoked, and it is not linked up with any user keyring. This is the
           recommended setting for system services, as this ensures that multiple services
           running under the same system user ID (in particular the root user) do not share their
           key material among each other. If shared is used a new session keyring is allocated as
           for private, but the user keyring of the user configured with User= is linked into it,
           so that keys assigned to the user may be requested by the unit's processes. In this
           mode multiple units running processes under the same user ID may share key material.
           Unless inherit is selected the unique invocation ID for the unit (see below) is added
           as a protected key by the name "invocation_id" to the newly created session keyring.
           Defaults to private for services of the system service manager and to inherit for
           non-service units and for services of the user service manager.

           Added in version 235.

       OOMScoreAdjust=
           Sets the adjustment value for the Linux kernel's Out-Of-Memory (OOM) killer score for
           executed processes. Takes an integer between -1000 (to disable OOM killing of
           processes of this unit) and 1000 (to make killing of processes of this unit under
           memory pressure very likely). See The /proc Filesystem[6] for details. If not
           specified defaults to the OOM score adjustment level of the service manager itself,
           which is normally at 0.

           Use the OOMPolicy= setting of service units to configure how the service manager shall
           react to the kernel OOM killer or systemd-oomd terminating a process of the service.
           See systemd.service(5) for details.

       TimerSlackNSec=
           Sets the timer slack in nanoseconds for the executed processes. The timer slack
           controls the accuracy of wake-ups triggered by timers. See prctl(2) for more
           information. Note that in contrast to most other time span definitions this parameter
           takes an integer value in nano-seconds if no unit is specified. The usual time units
           are understood too.

       Personality=
           Controls which kernel architecture uname(2) shall report, when invoked by unit
           processes. Takes one of the architecture identifiers arm64, arm64-be, arm, arm-be,
           x86, x86-64, ppc, ppc-le, ppc64, ppc64-le, s390 or s390x. Which personality
           architectures are supported depends on the kernel's native architecture. Usually the
           64-bit versions of the various system architectures support their immediate 32-bit
           personality architecture counterpart, but no others. For example, x86-64 systems
           support the x86-64 and x86 personalities but no others. The personality feature is
           useful when running 32-bit services on a 64-bit host system. If not specified, the
           personality is left unmodified and thus reflects the personality of the host system's
           kernel. This option is not useful on architectures for which only one native word
           width was ever available, such as m68k (32-bit only) or alpha (64-bit only).

           Added in version 209.

       IgnoreSIGPIPE=
           Takes a boolean argument. If true, SIGPIPE is ignored in the executed process.
           Defaults to true since SIGPIPE is generally only useful in shell pipelines.

SCHEDULING

       Nice=
           Sets the default nice level (scheduling priority) for executed processes. Takes an
           integer between -20 (highest priority) and 19 (lowest priority). In case of resource
           contention, smaller values mean more resources will be made available to the unit's
           processes, larger values mean less resources will be made available. See
           setpriority(2) for details.

       CPUSchedulingPolicy=
           Sets the CPU scheduling policy for executed processes. Takes one of other, batch,
           idle, fifo or rr. See sched_setscheduler(2) for details.

       CPUSchedulingPriority=
           Sets the CPU scheduling priority for executed processes. The available priority range
           depends on the selected CPU scheduling policy (see above). For real-time scheduling
           policies an integer between 1 (lowest priority) and 99 (highest priority) can be used.
           In case of CPU resource contention, smaller values mean less CPU time is made
           available to the service, larger values mean more. See sched_setscheduler(2) for
           details.

       CPUSchedulingResetOnFork=
           Takes a boolean argument. If true, elevated CPU scheduling priorities and policies
           will be reset when the executed processes call fork(2), and can hence not leak into
           child processes. See sched_setscheduler(2) for details. Defaults to false.

       CPUAffinity=
           Controls the CPU affinity of the executed processes. Takes a list of CPU indices or
           ranges separated by either whitespace or commas. Alternatively, takes a special "numa"
           value in which case systemd automatically derives allowed CPU range based on the value
           of NUMAMask= option. CPU ranges are specified by the lower and upper CPU indices
           separated by a dash. This option may be specified more than once, in which case the
           specified CPU affinity masks are merged. If the empty string is assigned, the mask is
           reset, all assignments prior to this will have no effect. See sched_setaffinity(2) for
           details.

       NUMAPolicy=
           Controls the NUMA memory policy of the executed processes. Takes a policy type, one
           of: default, preferred, bind, interleave and local. A list of NUMA nodes that should
           be associated with the policy must be specified in NUMAMask=. For more details on each
           policy please see, set_mempolicy(2). For overall overview of NUMA support in Linux
           see, numa(7).

           Added in version 243.

       NUMAMask=
           Controls the NUMA node list which will be applied alongside with selected NUMA policy.
           Takes a list of NUMA nodes and has the same syntax as a list of CPUs for CPUAffinity=
           option or special "all" value which will include all available NUMA nodes in the mask.
           Note that the list of NUMA nodes is not required for default and local policies and
           for preferred policy we expect a single NUMA node.

           Added in version 243.

       IOSchedulingClass=
           Sets the I/O scheduling class for executed processes. Takes one of the strings
           realtime, best-effort or idle. The kernel's default scheduling class is best-effort at
           a priority of 4. If the empty string is assigned to this option, all prior assignments
           to both IOSchedulingClass= and IOSchedulingPriority= have no effect. See ioprio_set(2)
           for details.

       IOSchedulingPriority=
           Sets the I/O scheduling priority for executed processes. Takes an integer between 0
           (highest priority) and 7 (lowest priority). In case of I/O contention, smaller values
           mean more I/O bandwidth is made available to the unit's processes, larger values mean
           less bandwidth. The available priorities depend on the selected I/O scheduling class
           (see above). If the empty string is assigned to this option, all prior assignments to
           both IOSchedulingClass= and IOSchedulingPriority= have no effect. For the kernel's
           default scheduling class (best-effort) this defaults to 4. See ioprio_set(2) for
           details.

SANDBOXING

       The following sandboxing options are an effective way to limit the exposure of the system
       towards the unit's processes. It is recommended to turn on as many of these options for
       each unit as is possible without negatively affecting the process' ability to operate.
       Note that many of these sandboxing features are gracefully turned off on systems where the
       underlying security mechanism is not available. For example, ProtectSystem= has no effect
       if the kernel is built without file system namespacing or if the service manager runs in a
       container manager that makes file system namespacing unavailable to its payload.
       Similarly, RestrictRealtime= has no effect on systems that lack support for SECCOMP system
       call filtering, or in containers where support for this is turned off.

       Also note that some sandboxing functionality is generally not available in user services
       (i.e. services run by the per-user service manager). Specifically, the various settings
       requiring file system namespacing support (such as ProtectSystem=) are not available, as
       the underlying kernel functionality is only accessible to privileged processes. However,
       most namespacing settings, that will not work on their own in user services, will work
       when used in conjunction with PrivateUsers=true.

       Note that the various options that turn directories read-only (such as ProtectSystem=,
       ReadOnlyPaths=, ...) do not affect the ability for programs to connect to and communicate
       with AF_UNIX sockets in these directories. These options cannot be used to lock down
       access to IPC services hence.

       ProtectSystem=
           Takes a boolean argument or the special values "full" or "strict". If true, mounts the
           /usr/ and the boot loader directories (/boot and /efi) read-only for processes invoked
           by this unit. If set to "full", the /etc/ directory is mounted read-only, too. If set
           to "strict" the entire file system hierarchy is mounted read-only, except for the API
           file system subtrees /dev/, /proc/ and /sys/ (protect these directories using
           PrivateDevices=, ProtectKernelTunables=, ProtectControlGroups=). This setting ensures
           that any modification of the vendor-supplied operating system (and optionally its
           configuration, and local mounts) is prohibited for the service. It is recommended to
           enable this setting for all long-running services, unless they are involved with
           system updates or need to modify the operating system in other ways. If this option is
           used, ReadWritePaths= may be used to exclude specific directories from being made
           read-only. Similar, StateDirectory=, LogsDirectory=, ... and related directory
           settings (see below) also exclude the specific directories from the effect of
           ProtectSystem=. This setting is implied if DynamicUser= is set. This setting cannot
           ensure protection in all cases. In general it has the same limitations as
           ReadOnlyPaths=, see below. Defaults to off.

           Added in version 214.

       ProtectHome=
           Takes a boolean argument or the special values "read-only" or "tmpfs". If true, the
           directories /home/, /root, and /run/user are made inaccessible and empty for processes
           invoked by this unit. If set to "read-only", the three directories are made read-only
           instead. If set to "tmpfs", temporary file systems are mounted on the three
           directories in read-only mode. The value "tmpfs" is useful to hide home directories
           not relevant to the processes invoked by the unit, while still allowing necessary
           directories to be made visible when listed in BindPaths= or BindReadOnlyPaths=.

           Setting this to "yes" is mostly equivalent to setting the three directories in
           InaccessiblePaths=. Similarly, "read-only" is mostly equivalent to ReadOnlyPaths=, and
           "tmpfs" is mostly equivalent to TemporaryFileSystem= with ":ro".

           It is recommended to enable this setting for all long-running services (in particular
           network-facing ones), to ensure they cannot get access to private user data, unless
           the services actually require access to the user's private data. This setting is
           implied if DynamicUser= is set. This setting cannot ensure protection in all cases. In
           general it has the same limitations as ReadOnlyPaths=, see below.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 214.

       RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=,
       ConfigurationDirectory=
           These options take a whitespace-separated list of directory names. The specified
           directory names must be relative, and may not include "..". If set, when the unit is
           started, one or more directories by the specified names will be created (including
           their parents) below the locations defined in the following table. Also, the
           corresponding environment variable will be defined with the full paths of the
           directories. If multiple directories are set, then in the environment variable the
           paths are concatenated with colon (":").

           Table 2. Automatic directory creation and environment variables
           ┌────────────────────────┬────────────────┬──────────────────────┬──────────────────────────┐
           │DirectoryBelow path forBelow path for userEnvironment              │
           │                        │ system unitsunitsvariable set             │
           ├────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
           │RuntimeDirectory=/run/$XDG_RUNTIME_DIR$RUNTIME_DIRECTORY       │
           ├────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
           │StateDirectory=/var/lib/$XDG_STATE_HOME$STATE_DIRECTORY         │
           ├────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
           │CacheDirectory=/var/cache/$XDG_CACHE_HOME$CACHE_DIRECTORY         │
           ├────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
           │LogsDirectory=/var/log/$XDG_STATE_HOME/log/ │ $LOGS_DIRECTORY          │
           ├────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
           │ConfigurationDirectory=/etc/$XDG_CONFIG_HOME$CONFIGURATION_DIRECTORY │
           └────────────────────────┴────────────────┴──────────────────────┴──────────────────────────┘
           In case of RuntimeDirectory= the innermost subdirectories are removed when the unit is
           stopped. It is possible to preserve the specified directories in this case if
           RuntimeDirectoryPreserve= is configured to restart or yes (see below). The directories
           specified with StateDirectory=, CacheDirectory=, LogsDirectory=,
           ConfigurationDirectory= are not removed when the unit is stopped.

           Except in case of ConfigurationDirectory=, the innermost specified directories will be
           owned by the user and group specified in User= and Group=. If the specified
           directories already exist and their owning user or group do not match the configured
           ones, all files and directories below the specified directories as well as the
           directories themselves will have their file ownership recursively changed to match
           what is configured. As an optimization, if the specified directories are already owned
           by the right user and group, files and directories below of them are left as-is, even
           if they do not match what is requested. The innermost specified directories will have
           their access mode adjusted to the what is specified in RuntimeDirectoryMode=,
           StateDirectoryMode=, CacheDirectoryMode=, LogsDirectoryMode= and
           ConfigurationDirectoryMode=.

           These options imply BindPaths= for the specified paths. When combined with
           RootDirectory= or RootImage= these paths always reside on the host and are mounted
           from there into the unit's file system namespace.

           If DynamicUser= is used, the logic for CacheDirectory=, LogsDirectory= and
           StateDirectory= is slightly altered: the directories are created below
           /var/cache/private, /var/log/private and /var/lib/private, respectively, which are
           host directories made inaccessible to unprivileged users, which ensures that access to
           these directories cannot be gained through dynamic user ID recycling. Symbolic links
           are created to hide this difference in behaviour. Both from perspective of the host
           and from inside the unit, the relevant directories hence always appear directly below
           /var/cache, /var/log and /var/lib.

           Use RuntimeDirectory= to manage one or more runtime directories for the unit and bind
           their lifetime to the daemon runtime. This is particularly useful for unprivileged
           daemons that cannot create runtime directories in /run/ due to lack of privileges, and
           to make sure the runtime directory is cleaned up automatically after use. For runtime
           directories that require more complex or different configuration or lifetime
           guarantees, please consider using tmpfiles.d(5).

           RuntimeDirectory=, StateDirectory=, CacheDirectory= and LogsDirectory= optionally
           support a second parameter, separated by ":". The second parameter will be interpreted
           as a destination path that will be created as a symlink to the directory. The symlinks
           will be created after any BindPaths= or TemporaryFileSystem= options have been set up,
           to make ephemeral symlinking possible. The same source can have multiple symlinks, by
           using the same first parameter, but a different second parameter.

           The directories defined by these options are always created under the standard paths
           used by systemd (/var/, /run/, /etc/, ...). If the service needs directories in a
           different location, a different mechanism has to be used to create them.

           tmpfiles.d(5) provides functionality that overlaps with these options. Using these
           options is recommended, because the lifetime of the directories is tied directly to
           the lifetime of the unit, and it is not necessary to ensure that the tmpfiles.d
           configuration is executed before the unit is started.

           To remove any of the directories created by these settings, use the systemctl clean
           ...  command on the relevant units, see systemctl(1) for details.

           Example: if a system service unit has the following,

               RuntimeDirectory=foo/bar baz

           the service manager creates /run/foo (if it does not exist), /run/foo/bar, and
           /run/baz. The directories /run/foo/bar and /run/baz except /run/foo are owned by the
           user and group specified in User= and Group=, and removed when the service is stopped.

           Example: if a system service unit has the following,

               RuntimeDirectory=foo/bar
               StateDirectory=aaa/bbb ccc

           then the environment variable "RUNTIME_DIRECTORY" is set with "/run/foo/bar", and
           "STATE_DIRECTORY" is set with "/var/lib/aaa/bbb:/var/lib/ccc".

           Example: if a system service unit has the following,

               RuntimeDirectory=foo:bar foo:baz

           the service manager creates /run/foo (if it does not exist), and /run/bar plus
           /run/baz as symlinks to /run/foo.

           Added in version 211.

       RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=, LogsDirectoryMode=,
       ConfigurationDirectoryMode=
           Specifies the access mode of the directories specified in RuntimeDirectory=,
           StateDirectory=, CacheDirectory=, LogsDirectory=, or ConfigurationDirectory=,
           respectively, as an octal number. Defaults to 0755. See "Permissions" in
           path_resolution(7) for a discussion of the meaning of permission bits.

           Added in version 234.

       RuntimeDirectoryPreserve=
           Takes a boolean argument or restart. If set to no (the default), the directories
           specified in RuntimeDirectory= are always removed when the service stops. If set to
           restart the directories are preserved when the service is both automatically and
           manually restarted. Here, the automatic restart means the operation specified in
           Restart=, and manual restart means the one triggered by systemctl restart foo.service.
           If set to yes, then the directories are not removed when the service is stopped. Note
           that since the runtime directory /run/ is a mount point of "tmpfs", then for system
           services the directories specified in RuntimeDirectory= are removed when the system is
           rebooted.

           Added in version 235.

       TimeoutCleanSec=
           Configures a timeout on the clean-up operation requested through systemctl clean ...,
           see systemctl(1) for details. Takes the usual time values and defaults to infinity,
           i.e. by default no timeout is applied. If a timeout is configured the clean operation
           will be aborted forcibly when the timeout is reached, potentially leaving resources on
           disk.

           Added in version 244.

       ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths=, NoExecPaths=
           Sets up a new file system namespace for executed processes. These options may be used
           to limit access a process has to the file system. Each setting takes a space-separated
           list of paths relative to the host's root directory (i.e. the system running the
           service manager). Note that if paths contain symlinks, they are resolved relative to
           the root directory set with RootDirectory=/RootImage=.

           Paths listed in ReadWritePaths= are accessible from within the namespace with the same
           access modes as from outside of it. Paths listed in ReadOnlyPaths= are accessible for
           reading only, writing will be refused even if the usual file access controls would
           permit this. Nest ReadWritePaths= inside of ReadOnlyPaths= in order to provide
           writable subdirectories within read-only directories. Use ReadWritePaths= in order to
           allow-list specific paths for write access if ProtectSystem=strict is used. Note that
           ReadWritePaths= cannot be used to gain write access to a file system whose superblock
           is mounted read-only. On Linux, for each mount point write access is granted only if
           the mount point itself and the file system superblock backing it are not marked
           read-only.  ReadWritePaths= only controls the former, not the latter, hence a
           read-only file system superblock remains protected.

           Paths listed in InaccessiblePaths= will be made inaccessible for processes inside the
           namespace along with everything below them in the file system hierarchy. This may be
           more restrictive than desired, because it is not possible to nest ReadWritePaths=,
           ReadOnlyPaths=, BindPaths=, or BindReadOnlyPaths= inside it. For a more flexible
           option, see TemporaryFileSystem=.

           Content in paths listed in NoExecPaths= are not executable even if the usual file
           access controls would permit this. Nest ExecPaths= inside of NoExecPaths= in order to
           provide executable content within non-executable directories.

           Non-directory paths may be specified as well. These options may be specified more than
           once, in which case all paths listed will have limited access from within the
           namespace. If the empty string is assigned to this option, the specific list is reset,
           and all prior assignments have no effect.

           Paths in ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths= and
           NoExecPaths= may be prefixed with "-", in which case they will be ignored when they do
           not exist. If prefixed with "+" the paths are taken relative to the root directory of
           the unit, as configured with RootDirectory=/RootImage=, instead of relative to the
           root directory of the host (see above). When combining "-" and "+" on the same path
           make sure to specify "-" first, and "+" second.

           Note that these settings will disconnect propagation of mounts from the unit's
           processes to the host. This means that this setting may not be used for services which
           shall be able to install mount points in the main mount namespace. For ReadWritePaths=
           and ReadOnlyPaths=, propagation in the other direction is not affected, i.e. mounts
           created on the host generally appear in the unit processes' namespace, and mounts
           removed on the host also disappear there too. In particular, note that mount
           propagation from host to unit will result in unmodified mounts to be created in the
           unit's namespace, i.e. writable mounts appearing on the host will be writable in the
           unit's namespace too, even when propagated below a path marked with ReadOnlyPaths=!
           Restricting access with these options hence does not extend to submounts of a
           directory that are created later on. This means the lock-down offered by that setting
           is not complete, and does not offer full protection.

           Note that the effect of these settings may be undone by privileged processes. In order
           to set up an effective sandboxed environment for a unit it is thus recommended to
           combine these settings with either CapabilityBoundingSet=~CAP_SYS_ADMIN or
           SystemCallFilter=~@mount.

           Please be extra careful when applying these options to API file systems (a list of
           them could be found in MountAPIVPS=), since they may be required for basic system
           functionalities. Moreover, /run/ needs to be writable for setting up mount namespace
           and propagation.

           Simple allow-list example using these directives:

               [Service]
               ReadOnlyPaths=/
               ReadWritePaths=/var /run
               InaccessiblePaths=-/lost+found
               NoExecPaths=/
               ExecPaths=/usr/sbin/my_daemon /usr/lib /usr/lib64

           These options are only available for system services, or for services running in
           per-user instances of the service manager in which case PrivateUsers= is implicitly
           enabled (requires unprivileged user namespaces support to be enabled in the kernel via
           the "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 231.

       TemporaryFileSystem=
           Takes a space-separated list of mount points for temporary file systems (tmpfs). If
           set, a new file system namespace is set up for executed processes, and a temporary
           file system is mounted on each mount point. This option may be specified more than
           once, in which case temporary file systems are mounted on all listed mount points. If
           the empty string is assigned to this option, the list is reset, and all prior
           assignments have no effect. Each mount point may optionally be suffixed with a colon
           (":") and mount options such as "size=10%" or "ro". By default, each temporary file
           system is mounted with "nodev,strictatime,mode=0755". These can be disabled by
           explicitly specifying the corresponding mount options, e.g., "dev" or "nostrictatime".

           This is useful to hide files or directories not relevant to the processes invoked by
           the unit, while necessary files or directories can be still accessed by combining with
           BindPaths= or BindReadOnlyPaths=:

           Example: if a unit has the following,

               TemporaryFileSystem=/var:ro
               BindReadOnlyPaths=/var/lib/systemd

           then the invoked processes by the unit cannot see any files or directories under /var/
           except for /var/lib/systemd or its contents.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 238.

       PrivateTmp=
           Takes a boolean argument. If true, sets up a new file system namespace for the
           executed processes and mounts private /tmp/ and /var/tmp/ directories inside it that
           are not shared by processes outside of the namespace. This is useful to secure access
           to temporary files of the process, but makes sharing between processes via /tmp/ or
           /var/tmp/ impossible. If true, all temporary files created by a service in these
           directories will be removed after the service is stopped. Defaults to false. It is
           possible to run two or more units within the same private /tmp/ and /var/tmp/
           namespace by using the JoinsNamespaceOf= directive, see systemd.unit(5) for details.
           This setting is implied if DynamicUser= is set. For this setting, the same
           restrictions regarding mount propagation and privileges apply as for ReadOnlyPaths=
           and related calls, see above. Enabling this setting has the side effect of adding
           Requires= and After= dependencies on all mount units necessary to access /tmp/ and
           /var/tmp/. Moreover an implicitly After= ordering on systemd-tmpfiles-setup.service(8)
           is added.

           Note that the implementation of this setting might be impossible (for example if mount
           namespaces are not available), and the unit should be written in a way that does not
           solely rely on this setting for security.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

       PrivateDevices=
           Takes a boolean argument. If true, sets up a new /dev/ mount for the executed
           processes and only adds API pseudo devices such as /dev/null, /dev/zero or /dev/random
           (as well as the pseudo TTY subsystem) to it, but no physical devices such as /dev/sda,
           system memory /dev/mem, system ports /dev/port and others. This is useful to turn off
           physical device access by the executed process. Defaults to false.

           Enabling this option will install a system call filter to block low-level I/O system
           calls that are grouped in the @raw-io set, remove CAP_MKNOD and CAP_SYS_RAWIO from the
           capability bounding set for the unit, and set DevicePolicy=closed (see
           systemd.resource-control(5) for details). Note that using this setting will disconnect
           propagation of mounts from the service to the host (propagation in the opposite
           direction continues to work). This means that this setting may not be used for
           services which shall be able to install mount points in the main mount namespace. The
           new /dev/ will be mounted read-only and 'noexec'. The latter may break old programs
           which try to set up executable memory by using mmap(2) of /dev/zero instead of using
           MAP_ANON. For this setting the same restrictions regarding mount propagation and
           privileges apply as for ReadOnlyPaths= and related calls, see above.

           Note that the implementation of this setting might be impossible (for example if mount
           namespaces are not available), and the unit should be written in a way that does not
           solely rely on this setting for security.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           When access to some but not all devices must be possible, the DeviceAllow= setting
           might be used instead. See systemd.resource-control(5).

           Added in version 209.

       PrivateNetwork=
           Takes a boolean argument. If true, sets up a new network namespace for the executed
           processes and configures only the loopback network device "lo" inside it. No other
           network devices will be available to the executed process. This is useful to turn off
           network access by the executed process. Defaults to false. It is possible to run two
           or more units within the same private network namespace by using the JoinsNamespaceOf=
           directive, see systemd.unit(5) for details. Note that this option will disconnect all
           socket families from the host, including AF_NETLINK and AF_UNIX. Effectively, for
           AF_NETLINK this means that device configuration events received from systemd-
           udevd.service(8) are not delivered to the unit's processes. And for AF_UNIX this has
           the effect that AF_UNIX sockets in the abstract socket namespace of the host will
           become unavailable to the unit's processes (however, those located in the file system
           will continue to be accessible).

           Note that the implementation of this setting might be impossible (for example if
           network namespaces are not available), and the unit should be written in a way that
           does not solely rely on this setting for security.

           When this option is enabled, PrivateMounts= is implied unless it is explicitly
           disabled, and /sys will be remounted to associate it with the new network namespace.

           When this option is used on a socket unit any sockets bound on behalf of this unit
           will be bound within a private network namespace. This may be combined with
           JoinsNamespaceOf= to listen on sockets inside of network namespaces of other services.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

       NetworkNamespacePath=
           Takes an absolute file system path referring to a Linux network namespace pseudo-file
           (i.e. a file like /proc/$PID/ns/net or a bind mount or symlink to one). When set the
           invoked processes are added to the network namespace referenced by that path. The path
           has to point to a valid namespace file at the moment the processes are forked off. If
           this option is used PrivateNetwork= has no effect. If this option is used together
           with JoinsNamespaceOf= then it only has an effect if this unit is started before any
           of the listed units that have PrivateNetwork= or NetworkNamespacePath= configured, as
           otherwise the network namespace of those units is reused.

           When this option is enabled, PrivateMounts= is implied unless it is explicitly
           disabled, and /sys will be remounted to associate it with the new network namespace.

           When this option is used on a socket unit any sockets bound on behalf of this unit
           will be bound within the specified network namespace.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 242.

       PrivateIPC=
           Takes a boolean argument. If true, sets up a new IPC namespace for the executed
           processes. Each IPC namespace has its own set of System V IPC identifiers and its own
           POSIX message queue file system. This is useful to avoid name clash of IPC
           identifiers. Defaults to false. It is possible to run two or more units within the
           same private IPC namespace by using the JoinsNamespaceOf= directive, see
           systemd.unit(5) for details.

           Note that IPC namespacing does not have an effect on AF_UNIX sockets, which are the
           most common form of IPC used on Linux. Instead, AF_UNIX sockets in the file system are
           subject to mount namespacing, and those in the abstract namespace are subject to
           network namespacing. IPC namespacing only has an effect on SysV IPC (which is mostly
           legacy) as well as POSIX message queues (for which AF_UNIX/SOCK_SEQPACKET sockets are
           typically a better replacement). IPC namespacing also has no effect on POSIX shared
           memory (which is subject to mount namespacing) either. See ipc_namespaces(7) for the
           details.

           Note that the implementation of this setting might be impossible (for example if IPC
           namespaces are not available), and the unit should be written in a way that does not
           solely rely on this setting for security.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 248.

       IPCNamespacePath=
           Takes an absolute file system path referring to a Linux IPC namespace pseudo-file
           (i.e. a file like /proc/$PID/ns/ipc or a bind mount or symlink to one). When set the
           invoked processes are added to the network namespace referenced by that path. The path
           has to point to a valid namespace file at the moment the processes are forked off. If
           this option is used PrivateIPC= has no effect. If this option is used together with
           JoinsNamespaceOf= then it only has an effect if this unit is started before any of the
           listed units that have PrivateIPC= or IPCNamespacePath= configured, as otherwise the
           network namespace of those units is reused.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 248.

       MemoryKSM=
           Takes a boolean argument. When set, it enables KSM (kernel samepage merging) for the
           processes. KSM is a memory-saving de-duplication feature. Anonymous memory pages with
           identical content can be replaced by a single write-protected page. This feature
           should only be enabled for jobs that share the same security domain. For details, see
           Kernel Samepage Merging[7] in the kernel documentation.

           Note that this functionality might not be available, for example if KSM is disabled in
           the kernel, or the kernel doesn't support controlling KSM at the process level through
           prctl(2).

           Added in version 254.

       PrivateUsers=
           Takes a boolean argument. If true, sets up a new user namespace for the executed
           processes and configures a minimal user and group mapping, that maps the "root" user
           and group as well as the unit's own user and group to themselves and everything else
           to the "nobody" user and group. This is useful to securely detach the user and group
           databases used by the unit from the rest of the system, and thus to create an
           effective sandbox environment. All files, directories, processes, IPC objects and
           other resources owned by users/groups not equaling "root" or the unit's own will stay
           visible from within the unit but appear owned by the "nobody" user and group. If this
           mode is enabled, all unit processes are run without privileges in the host user
           namespace (regardless if the unit's own user/group is "root" or not). Specifically
           this means that the process will have zero process capabilities on the host's user
           namespace, but full capabilities within the service's user namespace. Settings such as
           CapabilityBoundingSet= will affect only the latter, and there's no way to acquire
           additional capabilities in the host's user namespace. Defaults to off.

           When this setting is set up by a per-user instance of the service manager, the mapping
           of the "root" user and group to itself is omitted (unless the user manager is root).
           Additionally, in the per-user instance manager case, the user namespace will be set up
           before most other namespaces. This means that combining PrivateUsers=true with other
           namespaces will enable use of features not normally supported by the per-user
           instances of the service manager.

           This setting is particularly useful in conjunction with RootDirectory=/RootImage=, as
           the need to synchronize the user and group databases in the root directory and on the
           host is reduced, as the only users and groups who need to be matched are "root",
           "nobody" and the unit's own user and group.

           Note that the implementation of this setting might be impossible (for example if user
           namespaces are not available), and the unit should be written in a way that does not
           solely rely on this setting for security.

           Added in version 232.

       ProtectHostname=
           Takes a boolean argument. When set, sets up a new UTS namespace for the executed
           processes. In addition, changing hostname or domainname is prevented. Defaults to off.

           Note that the implementation of this setting might be impossible (for example if UTS
           namespaces are not available), and the unit should be written in a way that does not
           solely rely on this setting for security.

           Note that when this option is enabled for a service hostname changes no longer
           propagate from the system into the service, it is hence not suitable for services that
           need to take notice of system hostname changes dynamically.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 242.

       ProtectClock=
           Takes a boolean argument. If set, writes to the hardware clock or system clock will be
           denied. Defaults to off. Enabling this option removes CAP_SYS_TIME and CAP_WAKE_ALARM
           from the capability bounding set for this unit, installs a system call filter to block
           calls that can set the clock, and DeviceAllow=char-rtc r is implied. Note that the
           system calls are blocked altogether, the filter does not take into account that some
           of the calls can be used to read the clock state with some parameter combinations.
           Effectively, /dev/rtc0, /dev/rtc1, etc. are made read-only to the service. See
           systemd.resource-control(5) for the details about DeviceAllow=.

           It is recommended to turn this on for most services that do not need modify the clock
           or check its state.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 245.

       ProtectKernelTunables=
           Takes a boolean argument. If true, kernel variables accessible through /proc/sys/,
           /sys/, /proc/sysrq-trigger, /proc/latency_stats, /proc/acpi, /proc/timer_stats,
           /proc/fs and /proc/irq will be made read-only and /proc/kallsyms as well as
           /proc/kcore will be inaccessible to all processes of the unit. Usually, tunable kernel
           variables should be initialized only at boot-time, for example with the sysctl.d(5)
           mechanism. Few services need to write to these at runtime; it is hence recommended to
           turn this on for most services. For this setting the same restrictions regarding mount
           propagation and privileges apply as for ReadOnlyPaths= and related calls, see above.
           Defaults to off. Note that this option does not prevent indirect changes to kernel
           tunables effected by IPC calls to other processes. However, InaccessiblePaths= may be
           used to make relevant IPC file system objects inaccessible. If ProtectKernelTunables=
           is set, MountAPIVFS=yes is implied.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 232.

       ProtectKernelModules=
           Takes a boolean argument. If true, explicit module loading will be denied. This allows
           module load and unload operations to be turned off on modular kernels. It is
           recommended to turn this on for most services that do not need special file systems or
           extra kernel modules to work. Defaults to off. Enabling this option removes
           CAP_SYS_MODULE from the capability bounding set for the unit, and installs a system
           call filter to block module system calls, also /usr/lib/modules is made inaccessible.
           For this setting the same restrictions regarding mount propagation and privileges
           apply as for ReadOnlyPaths= and related calls, see above. Note that limited automatic
           module loading due to user configuration or kernel mapping tables might still happen
           as side effect of requested user operations, both privileged and unprivileged. To
           disable module auto-load feature please see sysctl.d(5) kernel.modules_disabled
           mechanism and /proc/sys/kernel/modules_disabled documentation.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 232.

       ProtectKernelLogs=
           Takes a boolean argument. If true, access to the kernel log ring buffer will be
           denied. It is recommended to turn this on for most services that do not need to read
           from or write to the kernel log ring buffer. Enabling this option removes CAP_SYSLOG
           from the capability bounding set for this unit, and installs a system call filter to
           block the syslog(2) system call (not to be confused with the libc API syslog(3) for
           userspace logging). The kernel exposes its log buffer to userspace via /dev/kmsg and
           /proc/kmsg. If enabled, these are made inaccessible to all the processes in the unit.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 244.

       ProtectControlGroups=
           Takes a boolean argument. If true, the Linux Control Groups (cgroups(7)) hierarchies
           accessible through /sys/fs/cgroup/ will be made read-only to all processes of the
           unit. Except for container managers no services should require write access to the
           control groups hierarchies; it is hence recommended to turn this on for most services.
           For this setting the same restrictions regarding mount propagation and privileges
           apply as for ReadOnlyPaths= and related calls, see above. Defaults to off. If
           ProtectControlGroups= is set, MountAPIVFS=yes is implied.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 232.

       RestrictAddressFamilies=
           Restricts the set of socket address families accessible to the processes of this unit.
           Takes "none", or a space-separated list of address family names to allow-list, such as
           AF_UNIX, AF_INET or AF_INET6. When "none" is specified, then all address families will
           be denied. When prefixed with "~" the listed address families will be applied as deny
           list, otherwise as allow list. Note that this restricts access to the socket(2) system
           call only. Sockets passed into the process by other means (for example, by using
           socket activation with socket units, see systemd.socket(5)) are unaffected. Also,
           sockets created with socketpair() (which creates connected AF_UNIX sockets only) are
           unaffected. Note that this option has no effect on 32-bit x86, s390, s390x, mips,
           mips-le, ppc, ppc-le, ppc64, ppc64-le and is ignored (but works correctly on other
           ABIs, including x86-64). Note that on systems supporting multiple ABIs (such as
           x86/x86-64) it is recommended to turn off alternative ABIs for services, so that they
           cannot be used to circumvent the restrictions of this option. Specifically, it is
           recommended to combine this option with SystemCallArchitectures=native or similar. By
           default, no restrictions apply, all address families are accessible to processes. If
           assigned the empty string, any previous address family restriction changes are undone.
           This setting does not affect commands prefixed with "+".

           Use this option to limit exposure of processes to remote access, in particular via
           exotic and sensitive network protocols, such as AF_PACKET. Note that in most cases,
           the local AF_UNIX address family should be included in the configured allow list as it
           is frequently used for local communication, including for syslog(2) logging.

           Added in version 211.

       RestrictFileSystems=
           Restricts the set of filesystems processes of this unit can open files on. Takes a
           space-separated list of filesystem names. Any filesystem listed is made accessible to
           the unit's processes, access to filesystem types not listed is prohibited
           (allow-listing). If the first character of the list is "~", the effect is inverted:
           access to the filesystems listed is prohibited (deny-listing). If the empty string is
           assigned, access to filesystems is not restricted.

           If you specify both types of this option (i.e. allow-listing and deny-listing), the
           first encountered will take precedence and will dictate the default action (allow
           access to the filesystem or deny it). Then the next occurrences of this option will
           add or delete the listed filesystems from the set of the restricted filesystems,
           depending on its type and the default action.

           Example: if a unit has the following,

               RestrictFileSystems=ext4 tmpfs
               RestrictFileSystems=ext2 ext4

           then access to ext4, tmpfs, and ext2 is allowed and access to other filesystems is
           denied.

           Example: if a unit has the following,

               RestrictFileSystems=ext4 tmpfs
               RestrictFileSystems=~ext4

           then only access tmpfs is allowed.

           Example: if a unit has the following,

               RestrictFileSystems=~ext4 tmpfs
               RestrictFileSystems=ext4

           then only access to tmpfs is denied.

           As the number of possible filesystems is large, predefined sets of filesystems are
           provided. A set starts with "@" character, followed by name of the set.

           Table 3. Currently predefined filesystem sets
           ┌──────────────────┬──────────────────────────────────┐
           │SetDescription                      │
           ├──────────────────┼──────────────────────────────────┤
           │@basic-api        │ Basic filesystem API.            │
           ├──────────────────┼──────────────────────────────────┤
           │@auxiliary-api    │ Auxiliary filesystem API.        │
           ├──────────────────┼──────────────────────────────────┤
           │@common-block     │ Common block device filesystems. │
           ├──────────────────┼──────────────────────────────────┤
           │@historical-block │ Historical block device          │
           │                  │ filesystems.                     │
           ├──────────────────┼──────────────────────────────────┤
           │@network          │ Well-known network filesystems.  │
           ├──────────────────┼──────────────────────────────────┤
           │@privileged-api   │ Privileged filesystem API.       │
           ├──────────────────┼──────────────────────────────────┤
           │@temporary        │ Temporary filesystems: tmpfs,    │
           │                  │ ramfs.                           │
           ├──────────────────┼──────────────────────────────────┤
           │@known            │ All known filesystems defined by │
           │                  │ the kernel. This list is defined │
           │                  │ statically in systemd based on a │
           │                  │ kernel version that was          │
           │                  │ available when this systemd      │
           │                  │ version was released. It will    │
           │                  │ become progressively more        │
           │                  │ out-of-date as the kernel is     │
           │                  │ updated.                         │
           └──────────────────┴──────────────────────────────────┘
           Use systemd-analyze(1)'s filesystems command to retrieve a list of filesystems defined
           on the local system.

           Note that this setting might not be supported on some systems (for example if the LSM
           eBPF hook is not enabled in the underlying kernel or if not using the unified control
           group hierarchy). In that case this setting has no effect.

           This option cannot be bypassed by prefixing "+" to the executable path in the service
           unit, as it applies to the whole control group.

           Added in version 250.

       RestrictNamespaces=
           Restricts access to Linux namespace functionality for the processes of this unit. For
           details about Linux namespaces, see namespaces(7). Either takes a boolean argument, or
           a space-separated list of namespace type identifiers. If false (the default), no
           restrictions on namespace creation and switching are made. If true, access to any kind
           of namespacing is prohibited. Otherwise, a space-separated list of namespace type
           identifiers must be specified, consisting of any combination of: cgroup, ipc, net,
           mnt, pid, user and uts. Any namespace type listed is made accessible to the unit's
           processes, access to namespace types not listed is prohibited (allow-listing). By
           prepending the list with a single tilde character ("~") the effect may be inverted:
           only the listed namespace types will be made inaccessible, all unlisted ones are
           permitted (deny-listing). If the empty string is assigned, the default namespace
           restrictions are applied, which is equivalent to false. This option may appear more
           than once, in which case the namespace types are merged by OR, or by AND if the lines
           are prefixed with "~" (see examples below). Internally, this setting limits access to
           the unshare(2), clone(2) and setns(2) system calls, taking the specified flags
           parameters into account. Note that — if this option is used — in addition to
           restricting creation and switching of the specified types of namespaces (or all of
           them, if true) access to the setns() system call with a zero flags parameter is
           prohibited. This setting is only supported on x86, x86-64, mips, mips-le, mips64,
           mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces no
           restrictions on other architectures.

           Example: if a unit has the following,

               RestrictNamespaces=cgroup ipc
               RestrictNamespaces=cgroup net

           then cgroup, ipc, and net are set. If the second line is prefixed with "~", e.g.,

               RestrictNamespaces=cgroup ipc
               RestrictNamespaces=~cgroup net

           then, only ipc is set.

           Added in version 233.

       LockPersonality=
           Takes a boolean argument. If set, locks down the personality(2) system call so that
           the kernel execution domain may not be changed from the default or the personality
           selected with Personality= directive. This may be useful to improve security, because
           odd personality emulations may be poorly tested and source of vulnerabilities.

           Added in version 235.

       MemoryDenyWriteExecute=
           Takes a boolean argument. If set, attempts to create memory mappings that are writable
           and executable at the same time, or to change existing memory mappings to become
           executable, or mapping shared memory segments as executable, are prohibited.
           Specifically, a system call filter is added (or preferably, an equivalent kernel check
           is enabled with prctl(2)) that rejects mmap(2) system calls with both PROT_EXEC and
           PROT_WRITE set, mprotect(2) or pkey_mprotect(2) system calls with PROT_EXEC set and
           shmat(2) system calls with SHM_EXEC set. Note that this option is incompatible with
           programs and libraries that generate program code dynamically at runtime, including
           JIT execution engines, executable stacks, and code "trampoline" feature of various C
           compilers. This option improves service security, as it makes harder for software
           exploits to change running code dynamically. However, the protection can be
           circumvented, if the service can write to a filesystem, which is not mounted with
           noexec (such as /dev/shm), or it can use memfd_create(). This can be prevented by
           making such file systems inaccessible to the service (e.g.
           InaccessiblePaths=/dev/shm) and installing further system call filters
           (SystemCallFilter=~memfd_create). Note that this feature is fully available on x86-64,
           and partially on x86. Specifically, the shmat() protection is not available on x86.
           Note that on systems supporting multiple ABIs (such as x86/x86-64) it is recommended
           to turn off alternative ABIs for services, so that they cannot be used to circumvent
           the restrictions of this option. Specifically, it is recommended to combine this
           option with SystemCallArchitectures=native or similar.

           Added in version 231.

       RestrictRealtime=
           Takes a boolean argument. If set, any attempts to enable realtime scheduling in a
           process of the unit are refused. This restricts access to realtime task scheduling
           policies such as SCHED_FIFO, SCHED_RR or SCHED_DEADLINE. See sched(7) for details
           about these scheduling policies. Realtime scheduling policies may be used to
           monopolize CPU time for longer periods of time, and may hence be used to lock up or
           otherwise trigger Denial-of-Service situations on the system. It is hence recommended
           to restrict access to realtime scheduling to the few programs that actually require
           them. Defaults to off.

           Added in version 231.

       RestrictSUIDSGID=
           Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
           set-group-ID (SGID) bits on files or directories will be denied (for details on these
           bits see inode(7)). As the SUID/SGID bits are mechanisms to elevate privileges, and
           allow users to acquire the identity of other users, it is recommended to restrict
           creation of SUID/SGID files to the few programs that actually require them. Note that
           this restricts marking of any type of file system object with these bits, including
           both regular files and directories (where the SGID is a different meaning than for
           files, see documentation). This option is implied if DynamicUser= is enabled. Defaults
           to off.

           Added in version 242.

       RemoveIPC=
           Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the
           user and group the processes of this unit are run as are removed when the unit is
           stopped. This setting only has an effect if at least one of User=, Group= and
           DynamicUser= are used. It has no effect on IPC objects owned by the root user.
           Specifically, this removes System V semaphores, as well as System V and POSIX shared
           memory segments and message queues. If multiple units use the same user or group the
           IPC objects are removed when the last of these units is stopped. This setting is
           implied if DynamicUser= is set.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 232.

       PrivateMounts=
           Takes a boolean parameter. If set, the processes of this unit will be run in their own
           private file system (mount) namespace with all mount propagation from the processes
           towards the host's main file system namespace turned off. This means any file system
           mount points established or removed by the unit's processes will be private to them
           and not be visible to the host. However, file system mount points established or
           removed on the host will be propagated to the unit's processes. See
           mount_namespaces(7) for details on file system namespaces. Defaults to off.

           When turned on, this executes three operations for each invoked process: a new
           CLONE_NEWNS namespace is created, after which all existing mounts are remounted to
           MS_SLAVE to disable propagation from the unit's processes to the host (but leaving
           propagation in the opposite direction in effect). Finally, the mounts are remounted
           again to the propagation mode configured with MountFlags=, see below.

           File system namespaces are set up individually for each process forked off by the
           service manager. Mounts established in the namespace of the process created by
           ExecStartPre= will hence be cleaned up automatically as soon as that process exits and
           will not be available to subsequent processes forked off for ExecStart= (and similar
           applies to the various other commands configured for units). Similarly,
           JoinsNamespaceOf= does not permit sharing kernel mount namespaces between units, it
           only enables sharing of the /tmp/ and /var/tmp/ directories.

           Other file system namespace unit settings — PrivateTmp=, PrivateDevices=,
           ProtectSystem=, ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=,
           BindPaths=, BindReadOnlyPaths=, ... — also enable file system namespacing in a fashion
           equivalent to this option. Hence it is primarily useful to explicitly request this
           behaviour if none of the other settings are used.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

           Added in version 239.

       MountFlags=
           Takes a mount propagation setting: shared, slave or private, which controls whether
           file system mount points in the file system namespaces set up for this unit's
           processes will receive or propagate mounts and unmounts from other file system
           namespaces. See mount(2) for details on mount propagation, and the three propagation
           flags in particular.

           This setting only controls the final propagation setting in effect on all mount points
           of the file system namespace created for each process of this unit. Other file system
           namespacing unit settings (see the discussion in PrivateMounts= above) will implicitly
           disable mount and unmount propagation from the unit's processes towards the host by
           changing the propagation setting of all mount points in the unit's file system
           namespace to slave first. Setting this option to shared does not reestablish
           propagation in that case.

           If not set – but file system namespaces are enabled through another file system
           namespace unit setting – shared mount propagation is used, but — as mentioned — as
           slave is applied first, propagation from the unit's processes to the host is still
           turned off.

           It is not recommended to use private mount propagation for units, as this means
           temporary mounts (such as removable media) of the host will stay mounted and thus
           indefinitely busy in forked off processes, as unmount propagation events won't be
           received by the file system namespace of the unit.

           Usually, it is best to leave this setting unmodified, and use higher level file system
           namespacing options instead, in particular PrivateMounts=, see above.

           This option is only available for system services, or for services running in per-user
           instances of the service manager in which case PrivateUsers= is implicitly enabled
           (requires unprivileged user namespaces support to be enabled in the kernel via the
           "kernel.unprivileged_userns_clone=" sysctl).

SYSTEM CALL FILTERING

       SystemCallFilter=
           Takes a space-separated list of system call names. If this setting is used, all system
           calls executed by the unit processes except for the listed ones will result in
           immediate process termination with the SIGSYS signal (allow-listing). (See
           SystemCallErrorNumber= below for changing the default action). If the first character
           of the list is "~", the effect is inverted: only the listed system calls will result
           in immediate process termination (deny-listing). Deny-listed system calls and system
           call groups may optionally be suffixed with a colon (":") and "errno" error number
           (between 0 and 4095) or errno name such as EPERM, EACCES or EUCLEAN (see errno(3) for
           a full list). This value will be returned when a deny-listed system call is triggered,
           instead of terminating the processes immediately. Special setting "kill" can be used
           to explicitly specify killing. This value takes precedence over the one given in
           SystemCallErrorNumber=, see below. This feature makes use of the Secure Computing Mode
           2 interfaces of the kernel ('seccomp filtering') and is useful for enforcing a minimal
           sandboxing environment. Note that the execve(), exit(), exit_group(), getrlimit(),
           rt_sigreturn(), sigreturn() system calls and the system calls for querying time and
           sleeping are implicitly allow-listed and do not need to be listed explicitly. This
           option may be specified more than once, in which case the filter masks are merged. If
           the empty string is assigned, the filter is reset, all prior assignments will have no
           effect. This does not affect commands prefixed with "+".

           Note that on systems supporting multiple ABIs (such as x86/x86-64) it is recommended
           to turn off alternative ABIs for services, so that they cannot be used to circumvent
           the restrictions of this option. Specifically, it is recommended to combine this
           option with SystemCallArchitectures=native or similar.

           Note that strict system call filters may impact execution and error handling code
           paths of the service invocation. Specifically, access to the execve() system call is
           required for the execution of the service binary — if it is blocked service invocation
           will necessarily fail. Also, if execution of the service binary fails for some reason
           (for example: missing service executable), the error handling logic might require
           access to an additional set of system calls in order to process and log this failure
           correctly. It might be necessary to temporarily disable system call filters in order
           to simplify debugging of such failures.

           If you specify both types of this option (i.e. allow-listing and deny-listing), the
           first encountered will take precedence and will dictate the default action
           (termination or approval of a system call). Then the next occurrences of this option
           will add or delete the listed system calls from the set of the filtered system calls,
           depending of its type and the default action. (For example, if you have started with
           an allow list rule for read() and write(), and right after it add a deny list rule for
           write(), then write() will be removed from the set.)

           As the number of possible system calls is large, predefined sets of system calls are
           provided. A set starts with "@" character, followed by name of the set.

           Table 4. Currently predefined system call sets
           ┌────────────────┬──────────────────────────────────┐
           │SetDescription                      │
           ├────────────────┼──────────────────────────────────┤
           │@aio            │ Asynchronous I/O (io_setup(2),   │
           │                │ io_submit(2), and related calls) │
           ├────────────────┼──────────────────────────────────┤
           │@basic-io       │ System calls for basic I/O:      │
           │                │ reading, writing, seeking, file  │
           │                │ descriptor duplication and       │
           │                │ closing (read(2), write(2), and  │
           │                │ related calls)                   │
           ├────────────────┼──────────────────────────────────┤
           │@chown          │ Changing file ownership          │
           │                │ (chown(2), fchownat(2), and      │
           │                │ related calls)                   │
           ├────────────────┼──────────────────────────────────┤
           │@clock          │ System calls for changing the    │
           │                │ system clock (adjtimex(2),       │
           │                │ settimeofday(2), and related     │
           │                │ calls)                           │
           ├────────────────┼──────────────────────────────────┤
           │@cpu-emulation  │ System calls for CPU emulation   │
           │                │ functionality (vm86(2) and       │
           │                │ related calls)                   │
           ├────────────────┼──────────────────────────────────┤
           │@debug          │ Debugging, performance           │
           │                │ monitoring and tracing           │
           │                │ functionality (ptrace(2),        │
           │                │ perf_event_open(2) and related   │
           │                │ calls)                           │
           ├────────────────┼──────────────────────────────────┤
           │@file-system    │ File system operations: opening, │
           │                │ creating files and directories   │
           │                │ for read and write, renaming and │
           │                │ removing them, reading file      │
           │                │ properties, or creating hard and │
           │                │ symbolic links                   │
           ├────────────────┼──────────────────────────────────┤
           │@io-event       │ Event loop system calls          │
           │                │ (poll(2), select(2), epoll(7),   │
           │                │ eventfd(2) and related calls)    │
           ├────────────────┼──────────────────────────────────┤
           │@ipc            │ Pipes, SysV IPC, POSIX Message   │
           │                │ Queues and other IPC             │
           │                │ (mq_overview(7), svipc(7))       │
           ├────────────────┼──────────────────────────────────┤
           │@keyring        │ Kernel keyring access (keyctl(2) │
           │                │ and related calls)               │
           ├────────────────┼──────────────────────────────────┤
           │@memlock        │ Locking of memory in RAM         │
           │                │ (mlock(2), mlockall(2) and       │
           │                │ related calls)                   │
           ├────────────────┼──────────────────────────────────┤
           │@module         │ Loading and unloading of kernel  │
           │                │ modules (init_module(2),         │
           │                │ delete_module(2) and related     │
           │                │ calls)                           │
           ├────────────────┼──────────────────────────────────┤
           │@mount          │ Mounting and unmounting of file  │
           │                │ systems (mount(2), chroot(2),    │
           │                │ and related calls)               │
           ├────────────────┼──────────────────────────────────┤
           │@network-io     │ Socket I/O (including local      │
           │                │ AF_UNIX): socket(7), unix(7)     │
           ├────────────────┼──────────────────────────────────┤
           │@obsolete       │ Unusual, obsolete or             │
           │                │ unimplemented (create_module(2), │
           │                │ gtty(2), ...)                    │
           ├────────────────┼──────────────────────────────────┤
           │@pkey           │ System calls that deal with      │
           │                │ memory protection keys           │
           │                │ (pkeys(7))                       │
           ├────────────────┼──────────────────────────────────┤
           │@privileged     │ All system calls which need      │
           │                │ super-user capabilities          │
           │                │ (capabilities(7))                │
           ├────────────────┼──────────────────────────────────┤
           │@process        │ Process control, execution,      │
           │                │ namespacing operations           │
           │                │ (clone(2), kill(2),              │
           │                │ namespaces(7), ...)              │
           ├────────────────┼──────────────────────────────────┤
           │@raw-io         │ Raw I/O port access (ioperm(2),  │
           │                │ iopl(2), pciconfig_read(), ...)  │
           ├────────────────┼──────────────────────────────────┤
           │@reboot         │ System calls for rebooting and   │
           │                │ reboot preparation (reboot(2),   │
           │                │ kexec(), ...)                    │
           ├────────────────┼──────────────────────────────────┤
           │@resources      │ System calls for changing        │
           │                │ resource limits, memory and      │
           │                │ scheduling parameters            │
           │                │ (setrlimit(2), setpriority(2),   │
           │                │ ...)                             │
           ├────────────────┼──────────────────────────────────┤
           │@sandbox        │ System calls for sandboxing      │
           │                │ programs (seccomp(2), Landlock   │
           │                │ system calls, ...)               │
           ├────────────────┼──────────────────────────────────┤
           │@setuid         │ System calls for changing user   │
           │                │ ID and group ID credentials,     │
           │                │ (setuid(2), setgid(2),           │
           │                │ setresuid(2), ...)               │
           ├────────────────┼──────────────────────────────────┤
           │@signal         │ System calls for manipulating    │
           │                │ and handling process signals     │
           │                │ (signal(2), sigprocmask(2), ...) │
           ├────────────────┼──────────────────────────────────┤
           │@swap           │ System calls for                 │
           │                │ enabling/disabling swap devices  │
           │                │ (swapon(2), swapoff(2))          │
           ├────────────────┼──────────────────────────────────┤
           │@sync           │ Synchronizing files and memory   │
           │                │ to disk (fsync(2), msync(2), and │
           │                │ related calls)                   │
           ├────────────────┼──────────────────────────────────┤
           │@system-service │ A reasonable set of system calls │
           │                │ used by common system services,  │
           │                │ excluding any special purpose    │
           │                │ calls. This is the recommended   │
           │                │ starting point for allow-listing │
           │                │ system calls for system          │
           │                │ services, as it contains what is │
           │                │ typically needed by system       │
           │                │ services, but excludes overly    │
           │                │ specific interfaces. For         │
           │                │ example, the following APIs are  │
           │                │ excluded: "@clock", "@mount",    │
           │                │ "@swap", "@reboot".              │
           ├────────────────┼──────────────────────────────────┤
           │@timer          │ System calls for scheduling      │
           │                │ operations by time (alarm(2),    │
           │                │ timer_create(2), ...)            │
           ├────────────────┼──────────────────────────────────┤
           │@known          │ All system calls defined by the  │
           │                │ kernel. This list is defined     │
           │                │ statically in systemd based on a │
           │                │ kernel version that was          │
           │                │ available when this systemd      │
           │                │ version was released. It will    │
           │                │ become progressively more        │
           │                │ out-of-date as the kernel is     │
           │                │ updated.                         │
           └────────────────┴──────────────────────────────────┘
           Note, that as new system calls are added to the kernel, additional system calls might
           be added to the groups above. Contents of the sets may also change between systemd
           versions. In addition, the list of system calls depends on the kernel version and
           architecture for which systemd was compiled. Use systemd-analyze syscall-filter to
           list the actual list of system calls in each filter.

           Generally, allow-listing system calls (rather than deny-listing) is the safer mode of
           operation. It is recommended to enforce system call allow lists for all long-running
           system services. Specifically, the following lines are a relatively safe basic choice
           for the majority of system services:

               [Service]
               SystemCallFilter=@system-service
               SystemCallErrorNumber=EPERM

           Note that various kernel system calls are defined redundantly: there are multiple
           system calls for executing the same operation. For example, the pidfd_send_signal()
           system call may be used to execute operations similar to what can be done with the
           older kill() system call, hence blocking the latter without the former only provides
           weak protection. Since new system calls are added regularly to the kernel as
           development progresses, keeping system call deny lists comprehensive requires constant
           work. It is thus recommended to use allow-listing instead, which offers the benefit
           that new system calls are by default implicitly blocked until the allow list is
           updated.

           Also note that a number of system calls are required to be accessible for the dynamic
           linker to work. The dynamic linker is required for running most regular programs
           (specifically: all dynamic ELF binaries, which is how most distributions build
           packaged programs). This means that blocking these system calls (which include open(),
           openat() or mmap()) will make most programs typically shipped with generic
           distributions unusable.

           It is recommended to combine the file system namespacing related options with
           SystemCallFilter=~@mount, in order to prohibit the unit's processes to undo the
           mappings. Specifically these are the options PrivateTmp=, PrivateDevices=,
           ProtectSystem=, ProtectHome=, ProtectKernelTunables=, ProtectControlGroups=,
           ProtectKernelLogs=, ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and
           ReadWritePaths=.

           Added in version 187.

       SystemCallErrorNumber=
           Takes an "errno" error number (between 1 and 4095) or errno name such as EPERM, EACCES
           or EUCLEAN, to return when the system call filter configured with SystemCallFilter= is
           triggered, instead of terminating the process immediately. See errno(3) for a full
           list of error codes. When this setting is not used, or when the empty string or the
           special setting "kill" is assigned, the process will be terminated immediately when
           the filter is triggered.

           Added in version 209.

       SystemCallArchitectures=
           Takes a space-separated list of architecture identifiers to include in the system call
           filter. The known architecture identifiers are the same as for ConditionArchitecture=
           described in systemd.unit(5), as well as x32, mips64-n32, mips64-le-n32, and the
           special identifier native. The special identifier native implicitly maps to the native
           architecture of the system (or more precisely: to the architecture the system manager
           is compiled for). By default, this option is set to the empty list, i.e. no filtering
           is applied.

           If this setting is used, processes of this unit will only be permitted to call native
           system calls, and system calls of the specified architectures. For the purposes of
           this option, the x32 architecture is treated as including x86-64 system calls.
           However, this setting still fulfills its purpose, as explained below, on x32.

           System call filtering is not equally effective on all architectures. For example, on
           x86 filtering of network socket-related calls is not possible, due to ABI limitations
           — a limitation that x86-64 does not have, however. On systems supporting multiple ABIs
           at the same time — such as x86/x86-64 — it is hence recommended to limit the set of
           permitted system call architectures so that secondary ABIs may not be used to
           circumvent the restrictions applied to the native ABI of the system. In particular,
           setting SystemCallArchitectures=native is a good choice for disabling non-native ABIs.

           System call architectures may also be restricted system-wide via the
           SystemCallArchitectures= option in the global configuration. See systemd-
           system.conf(5) for details.

           Added in version 209.

       SystemCallLog=
           Takes a space-separated list of system call names. If this setting is used, all system
           calls executed by the unit processes for the listed ones will be logged. If the first
           character of the list is "~", the effect is inverted: all system calls except the
           listed system calls will be logged. This feature makes use of the Secure Computing
           Mode 2 interfaces of the kernel ('seccomp filtering') and is useful for auditing or
           setting up a minimal sandboxing environment. This option may be specified more than
           once, in which case the filter masks are merged. If the empty string is assigned, the
           filter is reset, all prior assignments will have no effect. This does not affect
           commands prefixed with "+".

           Added in version 247.

ENVIRONMENT

       Environment=
           Sets environment variables for executed processes. Each line is unquoted using the
           rules described in "Quoting" section in systemd.syntax(7) and becomes a list of
           variable assignments. If you need to assign a value containing spaces or the equals
           sign to a variable, put quotes around the whole assignment. Variable expansion is not
           performed inside the strings and the "$" character has no special meaning. Specifier
           expansion is performed, see the "Specifiers" section in systemd.unit(5).

           This option may be specified more than once, in which case all listed variables will
           be set. If the same variable is listed twice, the later setting will override the
           earlier setting. If the empty string is assigned to this option, the list of
           environment variables is reset, all prior assignments have no effect.

           The names of the variables can contain ASCII letters, digits, and the underscore
           character. Variable names cannot be empty or start with a digit. In variable values,
           most characters are allowed, but non-printable characters are currently rejected.

           Example:

               Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

           gives three variables "VAR1", "VAR2", "VAR3" with the values "word1 word2", "word3",
           "$word 5 6".

           See environ(7) for details about environment variables.

           Note that environment variables are not suitable for passing secrets (such as
           passwords, key material, ...) to service processes. Environment variables set for a
           unit are exposed to unprivileged clients via D-Bus IPC, and generally not understood
           as being data that requires protection. Moreover, environment variables are propagated
           down the process tree, including across security boundaries (such as setuid/setgid
           executables), and hence might leak to processes that should not have access to the
           secret data. Use LoadCredential=, LoadCredentialEncrypted= or SetCredentialEncrypted=
           (see below) to pass data to unit processes securely.

       EnvironmentFile=
           Similar to Environment=, but reads the environment variables from a text file. The
           text file should contain newline-separated variable assignments. Empty lines, lines
           without an "=" separator, or lines starting with ";" or "#" will be ignored, which may
           be used for commenting. The file must be encoded with UTF-8. Valid characters are
           unicode scalar values[8] other than unicode noncharacters[9], U+0000 NUL, and U+FEFF
           unicode byte order mark[10]. Control codes other than NUL are allowed.

           In the file, an unquoted value after the "=" is parsed with the same backslash-escape
           rules as POSIX shell unquoted text[11], but unlike in a shell, interior whitespace is
           preserved and quotes after the first non-whitespace character are preserved. Leading
           and trailing whitespace (space, tab, carriage return) is discarded, but interior
           whitespace within the line is preserved verbatim. A line ending with a backslash will
           be continued to the following one, with the newline itself discarded. A backslash "\"
           followed by any character other than newline will preserve the following character, so
           that "\\" will become the value "\".

           In the file, a "'"-quoted value after the "=" can span multiple lines and contain any
           character verbatim other than single quote, like POSIX shell single-quoted text[12].
           No backslash-escape sequences are recognized. Leading and trailing whitespace outside
           of the single quotes is discarded.

           In the file, a """-quoted value after the "=" can span multiple lines, and the same
           escape sequences are recognized as in POSIX shell double-quoted text[13]. Backslash
           ("\") followed by any of ""\`$" will preserve that character. A backslash followed by
           newline is a line continuation, and the newline itself is discarded. A backslash
           followed by any other character is ignored; both the backslash and the following
           character are preserved verbatim. Leading and trailing whitespace outside of the
           double quotes is discarded.

           The argument passed should be an absolute filename or wildcard expression, optionally
           prefixed with "-", which indicates that if the file does not exist, it will not be
           read and no error or warning message is logged. This option may be specified more than
           once in which case all specified files are read. If the empty string is assigned to
           this option, the list of file to read is reset, all prior assignments have no effect.

           The files listed with this directive will be read shortly before the process is
           executed (more specifically, after all processes from a previous unit state
           terminated. This means you can generate these files in one unit state, and read it
           with this option in the next. The files are read from the file system of the service
           manager, before any file system changes like bind mounts take place).

           Settings from these files override settings made with Environment=. If the same
           variable is set twice from these files, the files will be read in the order they are
           specified and the later setting will override the earlier setting.

       PassEnvironment=
           Pass environment variables set for the system service manager to executed processes.
           Takes a space-separated list of variable names. This option may be specified more than
           once, in which case all listed variables will be passed. If the empty string is
           assigned to this option, the list of environment variables to pass is reset, all prior
           assignments have no effect. Variables specified that are not set for the system
           manager will not be passed and will be silently ignored. Note that this option is only
           relevant for the system service manager, as system services by default do not
           automatically inherit any environment variables set for the service manager itself.
           However, in case of the user service manager all environment variables are passed to
           the executed processes anyway, hence this option is without effect for the user
           service manager.

           Variables set for invoked processes due to this setting are subject to being
           overridden by those configured with Environment= or EnvironmentFile=.

           Example:

               PassEnvironment=VAR1 VAR2 VAR3

           passes three variables "VAR1", "VAR2", "VAR3" with the values set for those variables
           in PID1.

           See environ(7) for details about environment variables.

           Added in version 228.

       UnsetEnvironment=
           Explicitly unset environment variable assignments that would normally be passed from
           the service manager to invoked processes of this unit. Takes a space-separated list of
           variable names or variable assignments. This option may be specified more than once,
           in which case all listed variables/assignments will be unset. If the empty string is
           assigned to this option, the list of environment variables/assignments to unset is
           reset. If a variable assignment is specified (that is: a variable name, followed by
           "=", followed by its value), then any environment variable matching this precise
           assignment is removed. If a variable name is specified (that is a variable name
           without any following "=" or value), then any assignment matching the variable name,
           regardless of its value is removed. Note that the effect of UnsetEnvironment= is
           applied as final step when the environment list passed to executed processes is
           compiled. That means it may undo assignments from any configuration source, including
           assignments made through Environment= or EnvironmentFile=, inherited from the system
           manager's global set of environment variables, inherited via PassEnvironment=, set by
           the service manager itself (such as $NOTIFY_SOCKET and such), or set by a PAM module
           (in case PAMName= is used).

           See "Environment Variables in Spawned Processes" below for a description of how those
           settings combine to form the inherited environment. See environ(7) for general
           information about environment variables.

           Added in version 235.

LOGGING AND STANDARD INPUT/OUTPUT

       StandardInput=
           Controls where file descriptor 0 (STDIN) of the executed processes is connected to.
           Takes one of null, tty, tty-force, tty-fail, data, file:path, socket or fd:name.

           If null is selected, standard input will be connected to /dev/null, i.e. all read
           attempts by the process will result in immediate EOF.

           If tty is selected, standard input is connected to a TTY (as configured by TTYPath=,
           see below) and the executed process becomes the controlling process of the terminal.
           If the terminal is already being controlled by another process, the executed process
           waits until the current controlling process releases the terminal.

           tty-force is similar to tty, but the executed process is forcefully and immediately
           made the controlling process of the terminal, potentially removing previous
           controlling processes from the terminal.

           tty-fail is similar to tty, but if the terminal already has a controlling process
           start-up of the executed process fails.

           The data option may be used to configure arbitrary textual or binary data to pass via
           standard input to the executed process. The data to pass is configured via
           StandardInputText=/StandardInputData= (see below). Note that the actual file
           descriptor type passed (memory file, regular file, UNIX pipe, ...) might depend on the
           kernel and available privileges. In any case, the file descriptor is read-only, and
           when read returns the specified data followed by EOF.

           The file:path option may be used to connect a specific file system object to standard
           input. An absolute path following the ":" character is expected, which may refer to a
           regular file, a FIFO or special file. If an AF_UNIX socket in the file system is
           specified, a stream socket is connected to it. The latter is useful for connecting
           standard input of processes to arbitrary system services.

           The socket option is valid in socket-activated services only, and requires the
           relevant socket unit file (see systemd.socket(5) for details) to have Accept=yes set,
           or to specify a single socket only. If this option is set, standard input will be
           connected to the socket the service was activated from, which is primarily useful for
           compatibility with daemons designed for use with the traditional inetd(8) socket
           activation daemon ($LISTEN_FDS (and related) environment variables are not passed when
           socket value is configured).

           The fd:name option connects standard input to a specific, named file descriptor
           provided by a socket unit. The name may be specified as part of this option, following
           a ":" character (e.g.  "fd:foobar"). If no name is specified, the name "stdin" is
           implied (i.e.  "fd" is equivalent to "fd:stdin"). At least one socket unit defining
           the specified name must be provided via the Sockets= option, and the file descriptor
           name may differ from the name of its containing socket unit. If multiple matches are
           found, the first one will be used. See FileDescriptorName= in systemd.socket(5) for
           more details about named file descriptors and their ordering.

           This setting defaults to null, unless StandardInputText=/StandardInputData= are set,
           in which case it defaults to data.

       StandardOutput=
           Controls where file descriptor 1 (stdout) of the executed processes is connected to.
           Takes one of inherit, null, tty, journal, kmsg, journal+console, kmsg+console,
           file:path, append:path, truncate:path, socket or fd:name.

           inherit duplicates the file descriptor of standard input for standard output.

           null connects standard output to /dev/null, i.e. everything written to it will be
           lost.

           tty connects standard output to a tty (as configured via TTYPath=, see below). If the
           TTY is used for output only, the executed process will not become the controlling
           process of the terminal, and will not fail or wait for other processes to release the
           terminal.

           journal connects standard output with the journal, which is accessible via
           journalctl(1). Note that everything that is written to kmsg (see below) is implicitly
           stored in the journal as well, the specific option listed below is hence a superset of
           this one. (Also note that any external, additional syslog daemons receive their log
           data from the journal, too, hence this is the option to use when logging shall be
           processed with such a daemon.)

           kmsg connects standard output with the kernel log buffer which is accessible via
           dmesg(1), in addition to the journal. The journal daemon might be configured to send
           all logs to kmsg anyway, in which case this option is no different from journal.

           journal+console and kmsg+console work in a similar way as the two options above but
           copy the output to the system console as well.

           The file:path option may be used to connect a specific file system object to standard
           output. The semantics are similar to the same option of StandardInput=, see above. If
           path refers to a regular file on the filesystem, it is opened (created if it doesn't
           exist yet using privileges of the user executing the systemd process) for writing at
           the beginning of the file, but without truncating it. If standard input and output are
           directed to the same file path, it is opened only once — for reading as well as
           writing — and duplicated. This is particularly useful when the specified path refers
           to an AF_UNIX socket in the file system, as in that case only a single stream
           connection is created for both input and output.

           append:path is similar to file:path above, but it opens the file in append mode.

           truncate:path is similar to file:path above, but it truncates the file when opening
           it. For units with multiple command lines, e.g.  Type=oneshot services with multiple
           ExecStart=, or services with ExecCondition=, ExecStartPre= or ExecStartPost=, the
           output file is reopened and therefore re-truncated for each command line. If the
           output file is truncated while another process still has the file open, e.g. by an
           ExecReload= running concurrently with an ExecStart=, and the other process continues
           writing to the file without adjusting its offset, then the space between the file
           pointers of the two processes may be filled with NUL bytes, producing a sparse file.
           Thus, truncate:path is typically only useful for units where only one process runs at
           a time, such as services with a single ExecStart= and no ExecStartPost=, ExecReload=,
           ExecStop= or similar.

           socket connects standard output to a socket acquired via socket activation. The
           semantics are similar to the same option of StandardInput=, see above.

           The fd:name option connects standard output to a specific, named file descriptor
           provided by a socket unit. A name may be specified as part of this option, following a
           ":" character (e.g.  "fd:foobar"). If no name is specified, the name "stdout" is
           implied (i.e.  "fd" is equivalent to "fd:stdout"). At least one socket unit defining
           the specified name must be provided via the Sockets= option, and the file descriptor
           name may differ from the name of its containing socket unit. If multiple matches are
           found, the first one will be used. See FileDescriptorName= in systemd.socket(5) for
           more details about named descriptors and their ordering.

           If the standard output (or error output, see below) of a unit is connected to the
           journal or the kernel log buffer, the unit will implicitly gain a dependency of type
           After= on systemd-journald.socket (also see the "Implicit Dependencies" section
           above). Also note that in this case stdout (or stderr, see below) will be an AF_UNIX
           stream socket, and not a pipe or FIFO that can be reopened. This means when executing
           shell scripts the construct echo "hello" > /dev/stderr for writing text to stderr will
           not work. To mitigate this use the construct echo "hello" >&2 instead, which is mostly
           equivalent and avoids this pitfall.

           If StandardInput= is set to one of tty, tty-force, tty-fail, socket, or fd:name, this
           setting defaults to inherit.

           In other cases, this setting defaults to the value set with DefaultStandardOutput= in
           systemd-system.conf(5), which defaults to journal. Note that setting this parameter
           might result in additional dependencies to be added to the unit (see above).

       StandardError=
           Controls where file descriptor 2 (stderr) of the executed processes is connected to.
           The available options are identical to those of StandardOutput=, with some exceptions:
           if set to inherit the file descriptor used for standard output is duplicated for
           standard error, while fd:name will use a default file descriptor name of "stderr".

           This setting defaults to the value set with DefaultStandardError= in systemd-
           system.conf(5), which defaults to inherit. Note that setting this parameter might
           result in additional dependencies to be added to the unit (see above).

       StandardInputText=, StandardInputData=
           Configures arbitrary textual or binary data to pass via file descriptor 0 (STDIN) to
           the executed processes. These settings have no effect unless StandardInput= is set to
           data (which is the default if StandardInput= is not set otherwise, but
           StandardInputText=/StandardInputData= is). Use this option to embed process input data
           directly in the unit file.

           StandardInputText= accepts arbitrary textual data. C-style escapes for special
           characters as well as the usual "%"-specifiers are resolved. Each time this setting is
           used the specified text is appended to the per-unit data buffer, followed by a newline
           character (thus every use appends a new line to the end of the buffer). Note that
           leading and trailing whitespace of lines configured with this option is removed. If an
           empty line is specified the buffer is cleared (hence, in order to insert an empty
           line, add an additional "\n" to the end or beginning of a line).

           StandardInputData= accepts arbitrary binary data, encoded in Base64[14]. No escape
           sequences or specifiers are resolved. Any whitespace in the encoded version is ignored
           during decoding.

           Note that StandardInputText= and StandardInputData= operate on the same data buffer,
           and may be mixed in order to configure both binary and textual data for the same input
           stream. The textual or binary data is joined strictly in the order the settings appear
           in the unit file. Assigning an empty string to either will reset the data buffer.

           Please keep in mind that in order to maintain readability long unit file settings may
           be split into multiple lines, by suffixing each line (except for the last) with a "\"
           character (see systemd.unit(5) for details). This is particularly useful for large
           data configured with these two options. Example:

               ...
               StandardInput=data
               StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZXMgYW5kIHNvIGRv \
                                 IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \
                                 dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \
                                 J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \
                                 dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \
                                 ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \
                                 eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK
               ...

           Added in version 236.

       LogLevelMax=
           Configures filtering by log level of log messages generated by this unit. Takes a
           syslog log level, one of emerg (lowest log level, only highest priority messages),
           alert, crit, err, warning, notice, info, debug (highest log level, also lowest
           priority messages). See syslog(3) for details. By default no filtering is applied
           (i.e. the default maximum log level is debug). Use this option to configure the
           logging system to drop log messages of a specific service above the specified level.
           For example, set LogLevelMax=info in order to turn off debug logging of a particularly
           chatty unit. Note that the configured level is applied to any log messages written by
           any of the processes belonging to this unit, as well as any log messages written by
           the system manager process (PID 1) in reference to this unit, sent via any supported
           logging protocol. The filtering is applied early in the logging pipeline, before any
           kind of further processing is done. Moreover, messages which pass through this filter
           successfully might still be dropped by filters applied at a later stage in the logging
           subsystem. For example, MaxLevelStore= configured in journald.conf(5) might prohibit
           messages of higher log levels to be stored on disk, even though the per-unit
           LogLevelMax= permitted it to be processed.

           Added in version 236.

       LogExtraFields=
           Configures additional log metadata fields to include in all log records generated by
           processes associated with this unit, including systemd. This setting takes one or more
           journal field assignments in the format "FIELD=VALUE" separated by whitespace. See
           systemd.journal-fields(7) for details on the journal field concept. Even though the
           underlying journal implementation permits binary field values, this setting accepts
           only valid UTF-8 values. To include space characters in a journal field value, enclose
           the assignment in double quotes (").  The usual specifiers are expanded in all
           assignments (see below). Note that this setting is not only useful for attaching
           additional metadata to log records of a unit, but given that all fields and values are
           indexed may also be used to implement cross-unit log record matching. Assign an empty
           string to reset the list.

           Note that this functionality is currently only available in system services, not in
           per-user services.

           Added in version 236.

       LogRateLimitIntervalSec=, LogRateLimitBurst=
           Configures the rate limiting that is applied to log messages generated by this unit.
           If, in the time interval defined by LogRateLimitIntervalSec=, more messages than
           specified in LogRateLimitBurst= are logged by a service, all further messages within
           the interval are dropped until the interval is over. A message about the number of
           dropped messages is generated. The time specification for LogRateLimitIntervalSec= may
           be specified in the following units: "s", "min", "h", "ms", "us". See systemd.time(7)
           for details. The default settings are set by RateLimitIntervalSec= and RateLimitBurst=
           configured in journald.conf(5). Note that this only applies to log messages that are
           processed by the logging subsystem, i.e. by systemd-journald.service(8). This means
           that if you connect a service's stderr directly to a file via StandardOutput=file:...
           or a similar setting, the rate limiting will not be applied to messages written that
           way (but it will be enforced for messages generated via syslog(3) and similar
           functions).

           Added in version 240.

       LogFilterPatterns=
           Define an extended regular expression to filter log messages based on the MESSAGE=
           field of the structured message. If the first character of the pattern is "~", log
           entries matching the pattern should be discarded. This option takes a single pattern
           as an argument but can be used multiple times to create a list of allowed and denied
           patterns. If the empty string is assigned, the filter is reset, and all prior
           assignments will have no effect.

           Because the "~" character is used to define denied patterns, it must be replaced with
           "\x7e" to allow a message starting with "~". For example, "~foobar" would add a
           pattern matching "foobar" to the deny list, while "\x7efoobar" would add a pattern
           matching "~foobar" to the allow list.

           Log messages are tested against denied patterns (if any), then against allowed
           patterns (if any). If a log message matches any of the denied patterns, it is
           discarded immediately without considering allowed patterns. Remaining log messages are
           tested against allowed patterns. Messages matching against none of the allowed pattern
           are discarded. If no allowed patterns are defined, then all messages are processed
           directly after going through denied filters.

           Filtering is based on the unit for which LogFilterPatterns= is defined, meaning log
           messages coming from systemd(1) about the unit are not taken into account. Filtered
           log messages won't be forwarded to traditional syslog daemons, the kernel log buffer
           (kmsg), the systemd console, or sent as wall messages to all logged-in users.

           Note that this functionality is currently only available in system services, not in
           per-user services.

           Added in version 253.

       LogNamespace=
           Run the unit's processes in the specified journal namespace. Expects a short
           user-defined string identifying the namespace. If not used the processes of the
           service are run in the default journal namespace, i.e. their log stream is collected
           and processed by systemd-journald.service. If this option is used any log data
           generated by processes of this unit (regardless if via the syslog(), journal native
           logging or stdout/stderr logging) is collected and processed by an instance of the
           systemd-journald@.service template unit, which manages the specified namespace. The
           log data is stored in a data store independent from the default log namespace's data
           store. See systemd-journald.service(8) for details about journal namespaces.

           Internally, journal namespaces are implemented through Linux mount namespacing and
           over-mounting the directory that contains the relevant AF_UNIX sockets used for
           logging in the unit's mount namespace. Since mount namespaces are used this setting
           disconnects propagation of mounts from the unit's processes to the host, similarly to
           how ReadOnlyPaths= and similar settings describe above work. Journal namespaces may
           hence not be used for services that need to establish mount points on the host.

           When this option is used the unit will automatically gain ordering and requirement
           dependencies on the two socket units associated with the systemd-journald@.service
           instance so that they are automatically established prior to the unit starting up.
           Note that when this option is used log output of this service does not appear in the
           regular journalctl(1) output, unless the --namespace= option is used.

           This option is only available for system services and is not supported for services
           running in per-user instances of the service manager.

           Added in version 245.

       SyslogIdentifier=
           Sets the process name ("syslog tag") to prefix log lines sent to the logging system or
           the kernel log buffer with. If not set, defaults to the process name of the executed
           process. This option is only useful when StandardOutput= or StandardError= are set to
           journal or kmsg (or to the same settings in combination with +console) and only
           applies to log messages written to stdout or stderr.

       SyslogFacility=
           Sets the syslog facility identifier to use when logging. One of kern, user, mail,
           daemon, auth, syslog, lpr, news, uucp, cron, authpriv, ftp, local0, local1, local2,
           local3, local4, local5, local6 or local7. See syslog(3) for details. This option is
           only useful when StandardOutput= or StandardError= are set to journal or kmsg (or to
           the same settings in combination with +console), and only applies to log messages
           written to stdout or stderr. Defaults to daemon.

       SyslogLevel=
           The default syslog log level to use when logging to the logging system or the kernel
           log buffer. One of emerg, alert, crit, err, warning, notice, info, debug. See
           syslog(3) for details. This option is only useful when StandardOutput= or
           StandardError= are set to journal or kmsg (or to the same settings in combination with
           +console), and only applies to log messages written to stdout or stderr. Note that
           individual lines output by executed processes may be prefixed with a different log
           level which can be used to override the default log level specified here. The
           interpretation of these prefixes may be disabled with SyslogLevelPrefix=, see below.
           For details, see sd-daemon(3). Defaults to info.

       SyslogLevelPrefix=
           Takes a boolean argument. If true and StandardOutput= or StandardError= are set to
           journal or kmsg (or to the same settings in combination with +console), log lines
           written by the executed process that are prefixed with a log level will be processed
           with this log level set but the prefix removed. If set to false, the interpretation of
           these prefixes is disabled and the logged lines are passed on as-is. This only applies
           to log messages written to stdout or stderr. For details about this prefixing see sd-
           daemon(3). Defaults to true.

       TTYPath=
           Sets the terminal device node to use if standard input, output, or error are connected
           to a TTY (see above). Defaults to /dev/console.

       TTYReset=
           Reset the terminal device specified with TTYPath= before and after execution. Defaults
           to "no".

       TTYVHangup=
           Disconnect all clients which have opened the terminal device specified with TTYPath=
           before and after execution. Defaults to "no".

       TTYRows=, TTYColumns=
           Configure the size of the TTY specified with TTYPath=. If unset or set to the empty
           string, the kernel default is used.

           Added in version 250.

       TTYVTDisallocate=
           If the terminal device specified with TTYPath= is a virtual console terminal, try to
           deallocate the TTY before and after execution. This ensures that the screen and
           scrollback buffer is cleared. Defaults to "no".

CREDENTIALS

       LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]
           Pass a credential to the unit. Credentials are limited-size binary or textual objects
           that may be passed to unit processes. They are primarily used for passing
           cryptographic keys (both public and private) or certificates, user account information
           or identity information from host to services. The data is accessible from the unit's
           processes via the file system, at a read-only location that (if possible and
           permitted) is backed by non-swappable memory. The data is only accessible to the user
           associated with the unit, via the User=/DynamicUser= settings (as well as the
           superuser). When available, the location of credentials is exported as the
           $CREDENTIALS_DIRECTORY environment variable to the unit's processes.

           The LoadCredential= setting takes a textual ID to use as name for a credential plus a
           file system path, separated by a colon. The ID must be a short ASCII string suitable
           as filename in the filesystem, and may be chosen freely by the user. If the specified
           path is absolute it is opened as regular file and the credential data is read from it.
           If the absolute path refers to an AF_UNIX stream socket in the file system a
           connection is made to it (only once at unit start-up) and the credential data read
           from the connection, providing an easy IPC integration point for dynamically
           transferring credentials from other services.

           If the specified path is not absolute and itself qualifies as valid credential
           identifier it is attempted to find a credential that the service manager itself
           received under the specified name — which may be used to propagate credentials from an
           invoking environment (e.g. a container manager that invoked the service manager) into
           a service. If no matching system credential is found, the directories /etc/credstore/,
           /run/credstore/ and /usr/lib/credstore/ are searched for files under the credential's
           name — which hence are recommended locations for credential data on disk. If
           LoadCredentialEncrypted= is used /run/credstore.encrypted/, /etc/credstore.encrypted/,
           and /usr/lib/credstore.encrypted/ are searched as well.

           If the file system path is omitted it is chosen identical to the credential name, i.e.
           this is a terse way to declare credentials to inherit from the service manager into a
           service. This option may be used multiple times, each time defining an additional
           credential to pass to the unit.

           Note that if the path is not specified or a valid credential identifier is given, i.e.
           in the above two cases, a missing credential is not considered fatal.

           If an absolute path referring to a directory is specified, every file in that
           directory (recursively) will be loaded as a separate credential. The ID for each
           credential will be the provided ID suffixed with "_$FILENAME" (e.g., "Key_file1").
           When loading from a directory, symlinks will be ignored.

           The contents of the file/socket may be arbitrary binary or textual data, including
           newline characters and NUL bytes.

           The LoadCredentialEncrypted= setting is identical to LoadCredential=, except that the
           credential data is decrypted and authenticated before being passed on to the executed
           processes. Specifically, the referenced path should refer to a file or socket with an
           encrypted credential, as implemented by systemd-creds(1). This credential is loaded,
           decrypted, authenticated and then passed to the application in plaintext form, in the
           same way a regular credential specified via LoadCredential= would be. A credential
           configured this way may be symmetrically encrypted/authenticated with a secret key
           derived from the system's TPM2 security chip, or with a secret key stored in
           /var/lib/systemd/credentials.secret, or with both. Using encrypted and authenticated
           credentials improves security as credentials are not stored in plaintext and only
           authenticated and decrypted into plaintext the moment a service requiring them is
           started. Moreover, credentials may be bound to the local hardware and installations,
           so that they cannot easily be analyzed offline, or be generated externally. When
           DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow= is
           set, or PrivateDevices= is set, then this setting adds /dev/tpmrm0 with rw mode to
           DeviceAllow=. See systemd.resource-control(5) for the details about DevicePolicy= or
           DeviceAllow=.

           Note that encrypted credentials targeted for services of the per-user service manager
           must be encrypted with systemd-creds encrypt --user, and those for the system service
           manager without the --user switch. Encrypted credentials are always targeted to a
           specific user or the system as a whole, and it is ensured that per-user service
           managers cannot decrypt secrets intended for the system or for other users.

           The credential files/IPC sockets must be accessible to the service manager, but don't
           have to be directly accessible to the unit's processes: the credential data is read
           and copied into separate, read-only copies for the unit that are accessible to
           appropriately privileged processes. This is particularly useful in combination with
           DynamicUser= as this way privileged data can be made available to processes running
           under a dynamic UID (i.e. not a previously known one) without having to open up access
           to all users.

           In order to reference the path a credential may be read from within a ExecStart=
           command line use "${CREDENTIALS_DIRECTORY}/mycred", e.g.  "ExecStart=cat
           ${CREDENTIALS_DIRECTORY}/mycred". In order to reference the path a credential may be
           read from within a Environment= line use "%d/mycred", e.g.
           "Environment=MYCREDPATH=%d/mycred". For system services the path may also be
           referenced as "/run/credentials/UNITNAME" in cases where no interpolation is possible,
           e.g. configuration files of software that does not yet support credentials natively.
           $CREDENTIALS_DIRECTORY is considered the primary interface to look for credentials,
           though, since it also works for user services.

           Currently, an accumulated credential size limit of 1 MB per unit is enforced.

           The service manager itself may receive system credentials that can be propagated to
           services from a hosting container manager or VM hypervisor. See the Container
           Interface[15] documentation for details about the former. For the latter, pass
           DMI/SMBIOS[16] OEM string table entries (field type 11) with a prefix of
           "io.systemd.credential:" or "io.systemd.credential.binary:". In both cases a key/value
           pair separated by "=" is expected, in the latter case the right-hand side is Base64
           decoded when parsed (thus permitting binary data to be passed in). Example qemu[17]
           switch: "-smbios type=11,value=io.systemd.credential:xx=yy", or "-smbios
           type=11,value=io.systemd.credential.binary:rick=TmV2ZXIgR29ubmEgR2l2ZSBZb3UgVXA=".
           Alternatively, use the qemu "fw_cfg" node "opt/io.systemd.credentials/". Example qemu
           switch: "-fw_cfg name=opt/io.systemd.credentials/mycred,string=supersecret". They may
           also be passed from the UEFI firmware environment via systemd-stub(7), from the initrd
           (see systemd(1)), or be specified on the kernel command line using the
           "systemd.set_credential=" and "systemd.set_credential_binary=" switches (see
           systemd(1) – this is not recommended since unprivileged userspace can read the kernel
           command line).

           If referencing an AF_UNIX stream socket to connect to, the connection will originate
           from an abstract namespace socket, that includes information about the unit and the
           credential ID in its socket name. Use getpeername(2) to query this information. The
           returned socket name is formatted as NUL RANDOM "/unit/" UNIT "/" ID, i.e. a NUL byte
           (as required for abstract namespace socket names), followed by a random string
           (consisting of alphadecimal characters), followed by the literal string "/unit/",
           followed by the requesting unit name, followed by the literal character "/", followed
           by the textual credential ID requested. Example:
           "\0adf9d86b6eda275e/unit/foobar.service/credx" in case the credential "credx" is
           requested for a unit "foobar.service". This functionality is useful for using a single
           listening socket to serve credentials to multiple consumers.

           For further information see System and Service Credentials[18] documentation.

           Added in version 247.

       ImportCredential=GLOB
           Pass one or more credentials to the unit. Takes a credential name for which we'll
           attempt to find a credential that the service manager itself received under the
           specified name — which may be used to propagate credentials from an invoking
           environment (e.g. a container manager that invoked the service manager) into a
           service. If the credential name is a glob, all credentials matching the glob are
           passed to the unit. Matching credentials are searched for in the system credentials,
           the encrypted system credentials, and under /etc/credstore/, /run/credstore/,
           /usr/lib/credstore/, /run/credstore.encrypted/, /etc/credstore.encrypted/, and
           /usr/lib/credstore.encrypted/ in that order. When multiple credentials of the same
           name are found, the first one found is used.

           The globbing expression implements a restrictive subset of glob(7): only a single
           trailing "*" wildcard may be specified. Both "?"  and "[]" wildcards are not
           permitted, nor are "*" wildcards anywhere except at the end of the glob expression.

           When multiple credentials of the same name are found, credentials found by
           LoadCredential= and LoadCredentialEncrypted= take priority over credentials found by
           ImportCredential=.

           Added in version 254.

       SetCredential=ID:VALUE, SetCredentialEncrypted=ID:VALUE
           The SetCredential= setting is similar to LoadCredential= but accepts a literal value
           to use as data for the credential, instead of a file system path to read the data
           from. Do not use this option for data that is supposed to be secret, as it is
           accessible to unprivileged processes via IPC. It's only safe to use this for user IDs,
           public key material and similar non-sensitive data. For everything else use
           LoadCredential=. In order to embed binary data into the credential data use C-style
           escaping (i.e.  "\n" to embed a newline, or "\x00" to embed a NUL byte).

           The SetCredentialEncrypted= setting is identical to SetCredential= but expects an
           encrypted credential in literal form as value. This allows embedding confidential
           credentials securely directly in unit files. Use systemd-creds(1)' -p switch to
           generate suitable SetCredentialEncrypted= lines directly from plaintext credentials.
           For further details see LoadCredentialEncrypted= above.

           When multiple credentials of the same name are found, credentials found by
           LoadCredential=, LoadCredentialEncrypted= and ImportCredential= take priority over
           credentials found by SetCredential=. As such, SetCredential= will act as default if no
           credentials are found by any of the former. In this case not being able to retrieve
           the credential from the path specified in LoadCredential= or LoadCredentialEncrypted=
           is not considered fatal.

           Added in version 247.

SYSTEM V COMPATIBILITY

       UtmpIdentifier=
           Takes a four character identifier string for an utmp(5) and wtmp entry for this
           service. This should only be set for services such as getty implementations (such as
           agetty(8)) where utmp/wtmp entries must be created and cleared before and after
           execution, or for services that shall be executed as if they were run by a getty
           process (see below). If the configured string is longer than four characters, it is
           truncated and the terminal four characters are used. This setting interprets %I style
           string replacements. This setting is unset by default, i.e. no utmp/wtmp entries are
           created or cleaned up for this service.

       UtmpMode=
           Takes one of "init", "login" or "user". If UtmpIdentifier= is set, controls which type
           of utmp(5)/wtmp entries for this service are generated. This setting has no effect
           unless UtmpIdentifier= is set too. If "init" is set, only an INIT_PROCESS entry is
           generated and the invoked process must implement a getty-compatible utmp/wtmp logic.
           If "login" is set, first an INIT_PROCESS entry, followed by a LOGIN_PROCESS entry is
           generated. In this case, the invoked process must implement a login(1)-compatible
           utmp/wtmp logic. If "user" is set, first an INIT_PROCESS entry, then a LOGIN_PROCESS
           entry and finally a USER_PROCESS entry is generated. In this case, the invoked process
           may be any process that is suitable to be run as session leader. Defaults to "init".

           Added in version 225.

ENVIRONMENT VARIABLES IN SPAWNED PROCESSES

       Processes started by the service manager are executed with an environment variable block
       assembled from multiple sources. Processes started by the system service manager generally
       do not inherit environment variables set for the service manager itself (but this may be
       altered via PassEnvironment=), but processes started by the user service manager instances
       generally do inherit all environment variables set for the service manager itself.

       For each invoked process the list of environment variables set is compiled from the
       following sources:

       •   Variables globally configured for the service manager, using the DefaultEnvironment=
           setting in systemd-system.conf(5), the kernel command line option systemd.setenv=
           understood by systemd(1), or via systemctl(1) set-environment verb.

       •   Variables defined by the service manager itself (see the list below).

       •   Variables set in the service manager's own environment variable block (subject to
           PassEnvironment= for the system service manager).

       •   Variables set via Environment= in the unit file.

       •   Variables read from files specified via EnvironmentFile= in the unit file.

       •   Variables set by any PAM modules in case PAMName= is in effect, cf. pam_env(8).

       If the same environment variable is set by multiple of these sources, the later source —
       according to the order of the list above — wins. Note that as the final step all variables
       listed in UnsetEnvironment= are removed from the compiled environment variable list,
       immediately before it is passed to the executed process.

       The general philosophy is to expose a small curated list of environment variables to
       processes. Services started by the system manager (PID 1) will be started, without
       additional service-specific configuration, with just a few environment variables. The user
       manager inherits environment variables as any other system service, but in addition may
       receive additional environment variables from PAM, and, typically, additional imported
       variables when the user starts a graphical session. It is recommended to keep the
       environment blocks in both the system and user managers lean. Importing all variables
       inherited by the graphical session or by one of the user shells is strongly discouraged.

       Hint: systemd-run -P env and systemd-run --user -P env print the effective system and user
       service environment blocks.

   Environment Variables Set or Propagated by the Service Manager
       The following environment variables are propagated by the service manager or generated
       internally for each invoked process:

       $PATH
           Colon-separated list of directories to use when launching executables.  systemd uses a
           fixed value of "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system
           manager. In case of the user manager, a different path may be configured by the
           distribution. It is recommended to not rely on the order of entries, and have only one
           program with a given name in $PATH.

           Added in version 208.

       $LANG
           Locale. Can be set in locale.conf(5) or on the kernel command line (see systemd(1) and
           kernel-command-line(7)).

           Added in version 208.

       $USER, $LOGNAME, $HOME, $SHELL
           User name (twice), home directory, and the login shell.  $USER is set unconditionally,
           while $HOME, $LOGNAME, and $SHELL are only set for the units that have User= set and
           SetLoginEnvironment= unset or set to true. For user services, these variables are
           typically inherited from the user manager itself. See passwd(5).

           Added in version 208.

       $INVOCATION_ID
           Contains a randomized, unique 128-bit ID identifying each runtime cycle of the unit,
           formatted as 32 character hexadecimal string. A new ID is assigned each time the unit
           changes from an inactive state into an activating or active state, and may be used to
           identify this specific runtime cycle, in particular in data stored offline, such as
           the journal. The same ID is passed to all processes run as part of the unit.

           Added in version 232.

       $XDG_RUNTIME_DIR
           The directory to use for runtime objects (such as IPC objects) and volatile state. Set
           for all services run by the user systemd instance, as well as any system services that
           use PAMName= with a PAM stack that includes pam_systemd. See below and pam_systemd(8)
           for more information.

           Added in version 208.

       $RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY, $LOGS_DIRECTORY,
       $CONFIGURATION_DIRECTORY
           Absolute paths to the directories defined with RuntimeDirectory=, StateDirectory=,
           CacheDirectory=, LogsDirectory=, and ConfigurationDirectory= when those settings are
           used.

           Added in version 244.

       $CREDENTIALS_DIRECTORY
           An absolute path to the per-unit directory with credentials configured via
           ImportCredential=/LoadCredential=/SetCredential=. The directory is marked read-only
           and is placed in unswappable memory (if supported and permitted), and is only
           accessible to the UID associated with the unit via User= or DynamicUser= (and the
           superuser).

           Added in version 247.

       $MAINPID
           The PID of the unit's main process if it is known. This is only set for control
           processes as invoked by ExecReload= and similar.

           Added in version 209.

       $MANAGERPID
           The PID of the user systemd instance, set for processes spawned by it.

           Added in version 208.

       $LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
           Information about file descriptors passed to a service for socket activation. See
           sd_listen_fds(3).

           Added in version 208.

       $NOTIFY_SOCKET
           The socket sd_notify() talks to. See sd_notify(3).

           Added in version 229.

       $WATCHDOG_PID, $WATCHDOG_USEC
           Information about watchdog keep-alive notifications. See sd_watchdog_enabled(3).

           Added in version 229.

       $SYSTEMD_EXEC_PID
           The PID of the unit process (e.g. process invoked by ExecStart=). The child process
           can use this information to determine whether the process is directly invoked by the
           service manager or indirectly as a child of another process by comparing this value
           with the current PID (similarly to the scheme used in sd_listen_fds(3) with
           $LISTEN_PID and $LISTEN_FDS).

           Added in version 248.

       $TERM
           Terminal type, set only for units connected to a terminal (StandardInput=tty,
           StandardOutput=tty, or StandardError=tty). See termcap(5).

           Added in version 209.

       $LOG_NAMESPACE
           Contains the name of the selected logging namespace when the LogNamespace= service
           setting is used.

           Added in version 246.

       $JOURNAL_STREAM
           If the standard output or standard error output of the executed processes are
           connected to the journal (for example, by setting StandardError=journal)
           $JOURNAL_STREAM contains the device and inode numbers of the connection file
           descriptor, formatted in decimal, separated by a colon (":"). This permits invoked
           processes to safely detect whether their standard output or standard error output are
           connected to the journal. The device and inode numbers of the file descriptors should
           be compared with the values set in the environment variable to determine whether the
           process output is still connected to the journal. Note that it is generally not
           sufficient to only check whether $JOURNAL_STREAM is set at all as services might
           invoke external processes replacing their standard output or standard error output,
           without unsetting the environment variable.

           If both standard output and standard error of the executed processes are connected to
           the journal via a stream socket, this environment variable will contain information
           about the standard error stream, as that's usually the preferred destination for log
           data. (Note that typically the same stream is used for both standard output and
           standard error, hence very likely the environment variable contains device and inode
           information matching both stream file descriptors.)

           This environment variable is primarily useful to allow services to optionally upgrade
           their used log protocol to the native journal protocol (using sd_journal_print(3) and
           other functions) if their standard output or standard error output is connected to the
           journal anyway, thus enabling delivery of structured metadata along with logged
           messages.

           Added in version 231.

       $SERVICE_RESULT
           Only used for the service unit type. This environment variable is passed to all
           ExecStop= and ExecStopPost= processes, and encodes the service "result". Currently,
           the following values are defined:

           Table 5. Defined $SERVICE_RESULT values
           ┌──────────────────┬──────────────────────────────────┐
           │ValueMeaning                          │
           ├──────────────────┼──────────────────────────────────┤
           │"success"         │ The service ran successfully and │
           │                  │ exited cleanly.                  │
           ├──────────────────┼──────────────────────────────────┤
           │"protocol"        │ A protocol violation occurred:   │
           │                  │ the service did not take the     │
           │                  │ steps required by its unit       │
           │                  │ configuration (specifically what │
           │                  │ is configured in its Type=       │
           │                  │ setting).                        │
           ├──────────────────┼──────────────────────────────────┤
           │"timeout"         │ One of the steps timed out.      │
           ├──────────────────┼──────────────────────────────────┤
           │"exit-code"       │ Service process exited with a    │
           │                  │ non-zero exit code; see          │
           │                  │ $EXIT_CODE below for the actual  │
           │                  │ exit code returned.              │
           ├──────────────────┼──────────────────────────────────┤
           │"signal"          │ A service process was terminated │
           │                  │ abnormally by a signal, without  │
           │                  │ dumping core. See $EXIT_CODE     │
           │                  │ below for the actual signal      │
           │                  │ causing the termination.         │
           ├──────────────────┼──────────────────────────────────┤
           │"core-dump"       │ A service process terminated     │
           │                  │ abnormally with a signal and     │
           │                  │ dumped core. See $EXIT_CODE      │
           │                  │ below for the signal causing the │
           │                  │ termination.                     │
           ├──────────────────┼──────────────────────────────────┤
           │"watchdog"        │ Watchdog keep-alive ping was     │
           │                  │ enabled for the service, but the │
           │                  │ deadline was missed.             │
           ├──────────────────┼──────────────────────────────────┤
           │"exec-condition"  │ Service did not run because      │
           │                  │ ExecCondition= failed.           │
           ├──────────────────┼──────────────────────────────────┤
           │"oom-kill"        │ A service process was terminated │
           │                  │ by the Out-Of-Memory (OOM)       │
           │                  │ killer.                          │
           ├──────────────────┼──────────────────────────────────┤
           │"start-limit-hit" │ A start limit was defined for    │
           │                  │ the unit and it was hit, causing │
           │                  │ the unit to fail to start. See   │
           │                  │ systemd.unit(5)'s                │
           │                  │ StartLimitIntervalSec= and       │
           │                  │ StartLimitBurst= for details.    │
           ├──────────────────┼──────────────────────────────────┤
           │"resources"       │ A catch-all condition in case a  │
           │                  │ system operation failed.         │
           └──────────────────┴──────────────────────────────────┘
           This environment variable is useful to monitor failure or successful termination of a
           service. Even though this variable is available in both ExecStop= and ExecStopPost=,
           it is usually a better choice to place monitoring tools in the latter, as the former
           is only invoked for services that managed to start up correctly, and the latter covers
           both services that failed during their start-up and those which failed during their
           runtime.

           Added in version 232.

       $EXIT_CODE, $EXIT_STATUS
           Only defined for the service unit type. These environment variables are passed to all
           ExecStop=, ExecStopPost= processes and contain exit status/code information of the
           main process of the service. For the precise definition of the exit code and status,
           see wait(2).  $EXIT_CODE is one of "exited", "killed", "dumped".  $EXIT_STATUS
           contains the numeric exit code formatted as string if $EXIT_CODE is "exited", and the
           signal name in all other cases. Note that these environment variables are only set if
           the service manager succeeded to start and identify the main process of the service.

           Table 6. Summary of possible service result variable values
           ┌──────────────────────┬─────────────────────┬─────────────────────────────┐
           │$SERVICE_RESULT$EXIT_CODE$EXIT_STATUS                │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"success"             │"killed"             │ "HUP", "INT", "TERM",       │
           │                      │                     │ "PIPE"                      │
           │                      ├─────────────────────┼─────────────────────────────┤
           │                      │"exited"             │ "0"                         │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"protocol"            │not set              │ not set                     │
           │                      ├─────────────────────┼─────────────────────────────┤
           │                      │"exited"             │ "0"                         │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"timeout"             │"killed"             │ "TERM", "KILL"              │
           │                      ├─────────────────────┼─────────────────────────────┤
           │                      │"exited"             │ "0", "1", "2", "3", ...,    │
           │                      │                     │ "255"                       │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"exit-code"           │"exited"             │ "1", "2", "3", ...,         │
           │                      │                     │ "255"                       │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"signal"              │"killed"             │ "HUP", "INT", "KILL",       │
           │                      │                     │ ...                         │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"core-dump"           │"dumped"             │ "ABRT", "SEGV", "QUIT",     │
           │                      │                     │ ...                         │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"watchdog"            │"dumped"             │ "ABRT"                      │
           │                      ├─────────────────────┼─────────────────────────────┤
           │                      │"killed"             │ "TERM", "KILL"              │
           │                      ├─────────────────────┼─────────────────────────────┤
           │                      │"exited"             │ "0", "1", "2", "3", ...,    │
           │                      │                     │ "255"                       │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"exec-condition"      │"exited"             │ "1", "2", "3", "4", ...,    │
           │                      │                     │ "254"                       │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"oom-kill"            │"killed"             │ "TERM", "KILL"              │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"start-limit-hit"     │not set              │ not set                     │
           ├──────────────────────┼─────────────────────┼─────────────────────────────┤
           │"resources"           │any of the above     │ any of the above            │
           ├──────────────────────┴─────────────────────┴─────────────────────────────┤
           │Note: the process may be also terminated by a signal not sent by systemd. │
           │In particular the process may send an arbitrary signal to itself in a     │
           │handler for any of the non-maskable signals. Nevertheless, in the         │
           │"timeout" and "watchdog" rows above only the signals that systemd sends   │
           │have been included. Moreover, using SuccessExitStatus= additional exit    │
           │statuses may be declared to indicate clean termination, which is not      │
           │reflected by this table.                                                  │
           └──────────────────────────────────────────────────────────────────────────┘
           Added in version 232.

       $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE, $MONITOR_EXIT_STATUS, $MONITOR_INVOCATION_ID,
       $MONITOR_UNIT
           Only defined for the service unit type. Those environment variables are passed to all
           ExecStart= and ExecStartPre= processes which run in services triggered by OnFailure=
           or OnSuccess= dependencies.

           Variables $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE and $MONITOR_EXIT_STATUS take
           the same values as for ExecStop= and ExecStopPost= processes. Variables
           $MONITOR_INVOCATION_ID and $MONITOR_UNIT are set to the invocation id and unit name of
           the service which triggered the dependency.

           Note that when multiple services trigger the same unit, those variables will be not be
           passed. Consider using a template handler unit for that case instead:
           "OnFailure=handler@%n.service" for non-templated units, or
           "OnFailure=handler@%p-%i.service" for templated units.

           Added in version 251.

       $PIDFILE
           The path to the configured PID file, in case the process is forked off on behalf of a
           service that uses the PIDFile= setting, see systemd.service(5) for details. Service
           code may use this environment variable to automatically generate a PID file at the
           location configured in the unit file. This field is set to an absolute path in the
           file system.

           Added in version 242.

       $REMOTE_ADDR, $REMOTE_PORT
           If this is a unit started via per-connection socket activation (i.e. via a socket unit
           with Accept=yes), these environment variables contain the IP address and port number
           of the remote peer of the socket connection.

           Added in version 254.

       $TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC, $TRIGGER_TIMER_MONOTONIC_USEC
           If the unit was activated dynamically (e.g.: a corresponding path unit or timer unit),
           the unit that triggered it and other type-dependent information will be passed via
           these variables. Note that this information is provided in a best-effort way. For
           example, multiple triggers happening one after another will be coalesced and only one
           will be reported, with no guarantee as to which one it will be. Because of this, in
           most cases this variable will be primarily informational, i.e. useful for debugging
           purposes, is lossy, and should not be relied upon to propagate a comprehensive reason
           for activation.

           Added in version 252.

       $MEMORY_PRESSURE_WATCH, $MEMORY_PRESSURE_WRITE
           If memory pressure monitoring is enabled for this service unit, the path to watch and
           the data to write into it. See Memory Pressure Handling[19] for details about these
           variables and the service protocol data they convey.

           Added in version 254.

       $FDSTORE
           The maximum number of file descriptors that may be stored in the manager for the
           service. This variable is set when the file descriptor store is enabled for the
           service, i.e.  FileDescriptorStoreMax= is set to a non-zero value (see
           systemd.service(5) for details). Applications may check this environment variable
           before sending file descriptors to the service manager via sd_pid_notify_with_fds(3).

           Added in version 254.

       For system services, when PAMName= is enabled and pam_systemd is part of the selected PAM
       stack, additional environment variables defined by systemd may be set for services.
       Specifically, these are $XDG_SEAT, $XDG_VTNR, see pam_systemd(8) for details.

PROCESS EXIT CODES

       When invoking a unit process the service manager possibly fails to apply the execution
       parameters configured with the settings above. In that case the already created service
       process will exit with a non-zero exit code before the configured command line is
       executed. (Or in other words, the child process possibly exits with these error codes,
       after having been created by the fork(2) system call, but before the matching execve(2)
       system call is called.) Specifically, exit codes defined by the C library, by the LSB
       specification and by the systemd service manager itself are used.

       The following basic service exit codes are defined by the C library.

       Table 7. Basic C library exit codes
       ┌──────────┬───────────────┬───────────────────────┐
       │Exit CodeSymbolic NameDescription           │
       ├──────────┼───────────────┼───────────────────────┤
       │0         │ EXIT_SUCCESS  │ Generic success code. │
       ├──────────┼───────────────┼───────────────────────┤
       │1         │ EXIT_FAILURE  │ Generic failure or    │
       │          │               │ unspecified error.    │
       └──────────┴───────────────┴───────────────────────┘

       The following service exit codes are defined by the LSB specification[20].

       Table 8. LSB service exit codes
       ┌──────────┬──────────────────────┬──────────────────────────┐
       │Exit CodeSymbolic NameDescription              │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │2         │ EXIT_INVALIDARGUMENT │ Invalid or excess        │
       │          │                      │ arguments.               │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │3         │ EXIT_NOTIMPLEMENTED  │ Unimplemented feature.   │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │4         │ EXIT_NOPERMISSION    │ The user has             │
       │          │                      │ insufficient privileges. │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │5         │ EXIT_NOTINSTALLED    │ The program is not       │
       │          │                      │ installed.               │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │6         │ EXIT_NOTCONFIGURED   │ The program is not       │
       │          │                      │ configured.              │
       ├──────────┼──────────────────────┼──────────────────────────┤
       │7         │ EXIT_NOTRUNNING      │ The program is not       │
       │          │                      │ running.                 │
       └──────────┴──────────────────────┴──────────────────────────┘

       The LSB specification suggests that error codes 200 and above are reserved for
       implementations. Some of them are used by the service manager to indicate problems during
       process invocation:

       Table 9. systemd-specific exit codes
       ┌──────────┬──────────────────────────────┬─────────────────────────────────────────────┐
       │Exit CodeSymbolic NameDescription                                 │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │200       │ EXIT_CHDIR                   │ Changing to the                             │
       │          │                              │ requested working                           │
       │          │                              │ directory failed. See                       │
       │          │                              │ WorkingDirectory= above.                    │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │201       │ EXIT_NICE                    │ Failed to set up process                    │
       │          │                              │ scheduling priority                         │
       │          │                              │ (nice level). See Nice=                     │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │202       │ EXIT_FDS                     │ Failed to close unwanted                    │
       │          │                              │ file descriptors, or to                     │
       │          │                              │ adjust passed file                          │
       │          │                              │ descriptors.                                │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │203       │ EXIT_EXEC                    │ The actual process                          │
       │          │                              │ execution failed                            │
       │          │                              │ (specifically, the                          │
       │          │                              │ execve(2) system call).                     │
       │          │                              │ Most likely this is                         │
       │          │                              │ caused by a missing or                      │
       │          │                              │ non-accessible                              │
       │          │                              │ executable file.                            │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │204       │ EXIT_MEMORY                  │ Failed to perform an                        │
       │          │                              │ action due to memory                        │
       │          │                              │ shortage.                                   │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │205       │ EXIT_LIMITS                  │ Failed to adjust                            │
       │          │                              │ resource limits. See                        │
       │          │                              │ LimitCPU= and related                       │
       │          │                              │ settings above.                             │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │206       │ EXIT_OOM_ADJUST              │ Failed to adjust the OOM                    │
       │          │                              │ setting. See                                │
       │          │                              │ OOMScoreAdjust= above.                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │207       │ EXIT_SIGNAL_MASK             │ Failed to set process                       │
       │          │                              │ signal mask.                                │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │208       │ EXIT_STDIN                   │ Failed to set up                            │
       │          │                              │ standard input. See                         │
       │          │                              │ StandardInput= above.                       │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │209       │ EXIT_STDOUT                  │ Failed to set up                            │
       │          │                              │ standard output. See                        │
       │          │                              │ StandardOutput= above.                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │210       │ EXIT_CHROOT                  │ Failed to change root                       │
       │          │                              │ directory (chroot(2)).                      │
       │          │                              │ See                                         │
       │          │                              │ RootDirectory=/RootImage=                   │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │211       │ EXIT_IOPRIO                  │ Failed to set up IO                         │
       │          │                              │ scheduling priority. See                    │
       │          │                              │ IOSchedulingClass=/IOSchedulingPriority=    │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │212       │ EXIT_TIMERSLACK              │ Failed to set up timer slack. See           │
       │          │                              │ TimerSlackNSec= above.                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │213       │ EXIT_SECUREBITS              │ Failed to set process secure bits. See      │
       │          │                              │ SecureBits= above.                          │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │214       │ EXIT_SETSCHEDULER            │ Failed to set up CPU scheduling. See        │
       │          │                              │ CPUSchedulingPolicy=/CPUSchedulingPriority= │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │215       │ EXIT_CPUAFFINITY             │ Failed to set up CPU affinity. See          │
       │          │                              │ CPUAffinity= above.                         │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │216       │ EXIT_GROUP                   │ Failed to determine or change group         │
       │          │                              │ credentials. See                            │
       │          │                              │ Group=/SupplementaryGroups= above.          │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │217       │ EXIT_USER                    │ Failed to determine or change user          │
       │          │                              │ credentials, or to set up user namespacing. │
       │          │                              │ See User=/PrivateUsers= above.              │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │218       │ EXIT_CAPABILITIES            │ Failed to drop capabilities, or apply       │
       │          │                              │ ambient capabilities. See                   │
       │          │                              │ CapabilityBoundingSet=/AmbientCapabilities= │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │219       │ EXIT_CGROUP                  │ Setting up the service control group        │
       │          │                              │ failed.                                     │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │220       │ EXIT_SETSID                  │ Failed to create new process session.       │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │221       │ EXIT_CONFIRM                 │ Execution has been cancelled by the user.   │
       │          │                              │ See the systemd.confirm_spawn= kernel       │
       │          │                              │ command line setting on kernel-command-     │
       │          │                              │ line(7) for details.                        │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │222       │ EXIT_STDERR                  │ Failed to set up standard error output. See │
       │          │                              │ StandardError= above.                       │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │224       │ EXIT_PAM                     │ Failed to set up PAM session. See PAMName=  │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │225       │ EXIT_NETWORK                 │ Failed to set up network namespacing. See   │
       │          │                              │ PrivateNetwork= above.                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │226       │ EXIT_NAMESPACE               │ Failed to set up mount, UTS, or IPC         │
       │          │                              │ namespacing. See ReadOnlyPaths=,            │
       │          │                              │ ProtectHostname=, PrivateIPC=, and related  │
       │          │                              │ settings above.                             │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │227       │ EXIT_NO_NEW_PRIVILEGES       │ Failed to disable new privileges. See       │
       │          │                              │ NoNewPrivileges=yes above.                  │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │228       │ EXIT_SECCOMP                 │ Failed to apply system call filters. See    │
       │          │                              │ SystemCallFilter= and related settings      │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │229       │ EXIT_SELINUX_CONTEXT         │ Determining or changing SELinux context     │
       │          │                              │ failed. See SELinuxContext= above.          │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │230       │ EXIT_PERSONALITY             │ Failed to set up an execution domain        │
       │          │                              │ (personality). See Personality= above.      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │231       │ EXIT_APPARMOR_PROFILE        │ Failed to prepare changing AppArmor         │
       │          │                              │ profile. See AppArmorProfile= above.        │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │232       │ EXIT_ADDRESS_FAMILIES        │ Failed to restrict address families. See    │
       │          │                              │ RestrictAddressFamilies= above.             │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │233       │ EXIT_RUNTIME_DIRECTORY       │ Setting up runtime directory failed. See    │
       │          │                              │ RuntimeDirectory= and related settings      │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │235       │ EXIT_CHOWN                   │ Failed to adjust socket ownership. Used for │
       │          │                              │ socket units only.                          │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │236       │ EXIT_SMACK_PROCESS_LABEL     │ Failed to set SMACK label. See              │
       │          │                              │ SmackProcessLabel= above.                   │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │237       │ EXIT_KEYRING                 │ Failed to set up kernel keyring.            │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │238       │ EXIT_STATE_DIRECTORY         │ Failed to set up unit's state directory.    │
       │          │                              │ See StateDirectory= above.                  │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │239       │ EXIT_CACHE_DIRECTORY         │ Failed to set up unit's cache directory.    │
       │          │                              │ See CacheDirectory= above.                  │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │240       │ EXIT_LOGS_DIRECTORY          │ Failed to set up unit's logging directory.  │
       │          │                              │ See LogsDirectory= above.                   │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │241       │ EXIT_CONFIGURATION_DIRECTORY │ Failed to set up unit's configuration       │
       │          │                              │ directory. See ConfigurationDirectory=      │
       │          │                              │ above.                                      │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │242       │ EXIT_NUMA_POLICY             │ Failed to set up unit's NUMA memory policy. │
       │          │                              │ See NUMAPolicy= and NUMAMask= above.        │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │243       │ EXIT_CREDENTIALS             │ Failed to set up unit's credentials. See    │
       │          │                              │ ImportCredential=, LoadCredential= and      │
       │          │                              │ SetCredential= above.                       │
       ├──────────┼──────────────────────────────┼─────────────────────────────────────────────┤
       │245       │ EXIT_BPF                     │ Failed to apply BPF restrictions. See       │
       │          │                              │ RestrictFileSystems= above.                 │
       └──────────┴──────────────────────────────┴─────────────────────────────────────────────┘

       Finally, the BSD operating systems define a set of exit codes, typically defined on Linux
       systems too:

       Table 10. BSD exit codes
       ┌──────────┬────────────────┬──────────────────────────┐
       │Exit CodeSymbolic NameDescription              │
       ├──────────┼────────────────┼──────────────────────────┤
       │64        │ EX_USAGE       │ Command line usage error │
       ├──────────┼────────────────┼──────────────────────────┤
       │65        │ EX_DATAERR     │ Data format error        │
       ├──────────┼────────────────┼──────────────────────────┤
       │66        │ EX_NOINPUT     │ Cannot open input        │
       ├──────────┼────────────────┼──────────────────────────┤
       │67        │ EX_NOUSER      │ Addressee unknown        │
       ├──────────┼────────────────┼──────────────────────────┤
       │68        │ EX_NOHOST      │ Host name unknown        │
       ├──────────┼────────────────┼──────────────────────────┤
       │69        │ EX_UNAVAILABLE │ Service unavailable      │
       ├──────────┼────────────────┼──────────────────────────┤
       │70        │ EX_SOFTWARE    │ internal software error  │
       ├──────────┼────────────────┼──────────────────────────┤
       │71        │ EX_OSERR       │ System error (e.g.,      │
       │          │                │ can't fork)              │
       ├──────────┼────────────────┼──────────────────────────┤
       │72        │ EX_OSFILE      │ Critical OS file missing │
       ├──────────┼────────────────┼──────────────────────────┤
       │73        │ EX_CANTCREAT   │ Can't create (user)      │
       │          │                │ output file              │
       ├──────────┼────────────────┼──────────────────────────┤
       │74        │ EX_IOERR       │ Input/output error       │
       ├──────────┼────────────────┼──────────────────────────┤
       │75        │ EX_TEMPFAIL    │ Temporary failure; user  │
       │          │                │ is invited to retry      │
       ├──────────┼────────────────┼──────────────────────────┤
       │76        │ EX_PROTOCOL    │ Remote error in protocol │
       ├──────────┼────────────────┼──────────────────────────┤
       │77        │ EX_NOPERM      │ Permission denied        │
       ├──────────┼────────────────┼──────────────────────────┤
       │78        │ EX_CONFIG      │ Configuration error      │
       └──────────┴────────────────┴──────────────────────────┘

EXAMPLES

       Example 3. $MONITOR_* usage

       A service myfailer.service which can trigger an OnFailure= dependency.

           [Unit]
           Description=Service which can trigger an OnFailure= dependency
           OnFailure=myhandler.service

           [Service]
           ExecStart=/bin/myprogram

       A service mysuccess.service which can trigger an OnSuccess= dependency.

           [Unit]
           Description=Service which can trigger an OnSuccess= dependency
           OnSuccess=myhandler.service

           [Service]
           ExecStart=/bin/mysecondprogram

       A service myhandler.service which can be triggered by any of the above services.

           [Unit]
           Description=Acts on service failing or succeeding

           [Service]
           ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"

       If myfailer.service were to run and exit in failure, then myhandler.service would be
       triggered and the monitor variables would be set as follows:

           MONITOR_SERVICE_RESULT=exit-code
           MONITOR_EXIT_CODE=exited
           MONITOR_EXIT_STATUS=1
           MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236
           MONITOR_UNIT=myfailer.service

       If mysuccess.service were to run and exit in success, then myhandler.service would be
       triggered and the monitor variables would be set as follows:

           MONITOR_SERVICE_RESULT=success
           MONITOR_EXIT_CODE=exited
           MONITOR_EXIT_STATUS=0
           MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697
           MONITOR_UNIT=mysuccess.service

SEE ALSO

       systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-system.conf(5),
       systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd.mount(5),
       systemd.kill(5), systemd.resource-control(5), systemd.time(7), systemd.directives(7),
       tmpfiles.d(5), exec(3), fork(2)

NOTES

        1. Discoverable Partitions Specification
           https://uapi-group.org/specifications/specs/discoverable_partitions_specification

        2. The /proc Filesystem
           https://docs.kernel.org/filesystems/proc.html#mount-options

        3. User/Group Name Syntax
           https://systemd.io/USER_NAMES

        4. No New Privileges Flag
           https://docs.kernel.org/userspace-api/no_new_privs.html

        5. JSON User Record
           https://systemd.io/USER_RECORD

        6. The /proc Filesystem
           https://docs.kernel.org/filesystems/proc.html

        7. Kernel Samepage Merging
           https://docs.kernel.org/admin-guide/mm/ksm.html

        8. unicode scalar values
           https://www.unicode.org/glossary/#unicode_scalar_value

        9. unicode noncharacters
           https://www.unicode.org/glossary/#noncharacter

       10. unicode byte order mark
           https://www.unicode.org/glossary/#byte_order_mark

       11. POSIX shell unquoted text
           https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01

       12. POSIX shell single-quoted text
           https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_02

       13. POSIX shell double-quoted text
           https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03

       14. Base64
           https://tools.ietf.org/html/rfc2045#section-6.8

       15. Container Interface
           https://systemd.io/CONTAINER_INTERFACE

       16. DMI/SMBIOS
           https://www.dmtf.org/standards/smbios

       17. qemu
           https://www.qemu.org/docs/master/system/index.html

       18. System and Service Credentials
           https://systemd.io/CREDENTIALS

       19. Memory Pressure Handling
           https://systemd.io/MEMORY_PRESSURE

       20. LSB specification
           https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html