Provided by: systemd_255.4-1ubuntu8.11_amd64 
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 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 chroot() jail. 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
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.
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.
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=.
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.
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 $HOME, $LOGNAME, and $SHELL environment
variables. If unset, this is controlled by whether User= is set. If true, they will always be set for
system services, i.e. even when the default user "root" is used. If false, the mentioned variables
are not set by systemd, no matter whether User= is used or not. This option normally has no effect on
user services, since 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
┌──────────────────┬───────────────────┬─────────────────────┬────────────────────────┐
│ Directive │ ulimit equivalent │ Unit │ Notes │
├──────────────────┼───────────────────┼─────────────────────┼────────────────────────┤
│ 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 careful │
│ │ │ Descriptors │ 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.
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. 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
┌─────────────────────────┬───────────────────────┬──────────────────────┬──────────────────────────┐
│ Directory │ Below path for system │ Below path for user │ Environment variable │
│ │ units │ units │ 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 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
┌───────────────────┬───────────────────────────────────────┐
│ Set │ Description │
├───────────────────┼───────────────────────────────────────┤
│ @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 — PrivateMounts=, PrivateTmp=, PrivateDevices=,
ProtectSystem=, ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=, ... — 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
┌─────────────────┬───────────────────────────────────────┐
│ Set │ Description │
├─────────────────┼───────────────────────────────────────┤
│ @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) 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 re-opened. 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.
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 will be discarded, whatever the allowed
patterns. Then, 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.
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 $CREDENTIALS_DIRECTORY environment variable
to the unit's processes.
The LoadCredential= setting takes a textual ID to use as name for a credential plus a file system
path, separated by a colon. The ID must be a short ASCII string suitable as filename in the
filesystem, and may be chosen freely by the user. If the specified path is absolute it is opened as
regular file and the credential data is read from it. If the absolute path refers to an AF_UNIX
stream socket in the file system a connection is made to it (only once at unit start-up) and the
credential data read from the connection, providing an easy IPC integration point for dynamically
transferring credentials from other services.
If the specified path is not absolute and itself qualifies as valid credential identifier it is
attempted to find a credential that the service manager itself received under the specified name —
which may be used to propagate credentials from an invoking environment (e.g. a container manager
that invoked the service manager) into a service. If no matching system credential is found, the
directories /etc/credstore/, /run/credstore/ and /usr/lib/credstore/ are searched for files under the
credential's name — which hence are recommended locations for credential data on disk. If
LoadCredentialEncrypted= is used /run/credstore.encrypted/, /etc/credstore.encrypted/, and
/usr/lib/credstore.encrypted/ are searched as well.
If the file system path is omitted it is chosen identical to the credential name, i.e. this is a
terse way to declare credentials to inherit from the service manager into a service. This option may
be used multiple times, each time defining an additional credential to pass to the unit.
If an absolute path referring to a directory is specified, every file in that directory (recursively)
will be loaded as a separate credential. The ID for each credential will be the provided ID suffixed
with "_$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=.
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
┌───────────────────┬───────────────────────────────────────┐
│ Value │ Meaning │
├───────────────────┼───────────────────────────────────────┤
│ "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 Code │ Symbolic Name │ Description │
├───────────┼───────────────┼───────────────────────┤
│ 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 Code │ Symbolic Name │ Description │
├───────────┼──────────────────────┼──────────────────────────────┤
│ 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 Code │ Symbolic Name │ Description │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 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 Code │ Symbolic Name │ Description │
├───────────┼────────────────┼────────────────────────────┤
│ 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
systemd 255 SYSTEMD.EXEC(5)