Ubuntu Manpage: systemd.exec - Execution environment configuration

Provided by: systemd_204-5ubuntu20.31_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.

OPTIONS

WorkingDirectory=
Takes an absolute directory path. Sets the working directory for executed processes.
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.

RootDirectory=
Takes an absolute directory path. Sets the root directory for executed processes, with
the chroot(2) system call. If this is used it must be ensured that the process and all
its auxiliary files are available in the chroot() jail.

User=, Group=
Sets the Unix user or group that the processes are executed as, respectively. Takes a
single user or group name or ID as argument. If no group is set, the default group of
the user is chosen.

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.

Nice=
Sets the default nice level (scheduling priority) for executed processes. Takes an
integer between -20 (highest priority) and 19 (lowest priority). See setpriority(2)
for details.

OOMScoreAdjust=
Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes
an integer between -1000 (to disable OOM killing for this process) and 1000 (to make
killing of this process under memory pressure very likely). See proc.txt[1] for
details.

IOSchedulingClass=
Sets the IO scheduling class for executed processes. Takes an integer between 0 and 3
or one of the strings none, realtime, best-effort or idle. See ioprio_set(2) for
details.

IOSchedulingPriority=
Sets the IO scheduling priority for executed processes. Takes an integer between 0
(highest priority) and 7 (lowest priority). The available priorities depend on the
selected IO scheduling class (see above). See ioprio_set(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.
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 fork, 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 space-separated list of
CPU indexes. This option may be specified more than once in which case the specificed
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.

UMask=
Controls the file mode creation mask. Takes an access mode in octal notation. See
umask(2) for details. Defaults to 0022.

Environment=
Sets environment variables for executed processes. Takes a space-separated list of
variable assignments. This option may be specified more than once in which case all
listed variables will be set. If the same variable is set 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. Variable
expansion is not performed inside the strings, and $ has no special meaning. If you
need to assign a value containing spaces to a variable, use double quotes (") for the
assignment.

Example:

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

gives three variables VAR1, VAR2, VAR3.

See environ(7) for details about environment variables.

EnvironmentFile=
Similar to Environment= but reads the environment variables from a text file. The text
file should contain new-line separated variable assignments. Empty lines and lines
starting with ; or # will be ignored, which may be used for commenting. A line ending
with a backslash will be concatenated with the following one, allowing multiline
variable definitions. The parser strips leading and trailing whitespace from the
values of assignments, unless you use double quotes (").

The argument passed should be an absolute file name or wildcard expression, optionally
prefixed with "-", which indicates that if the file does not exist it won't 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. 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.

StandardInput=
Controls where file descriptor 0 (STDIN) of the executed processes is connected to.
Takes one of null, tty, tty-force, tty-fail or socket. 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 socket option is only valid in socket-activated services, and only when the socket
configuration file (see systemd.socket(5) for details) specifies 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) daemon. This setting defaults to null.

StandardOutput=
Controls where file descriptor 1 (STDOUT) of the executed processes is connected to.
Takes one of inherit, null, tty, syslog, kmsg, journal, syslog+console, kmsg+console,
journal+console or socket. If set to inherit the file descriptor of standard input is
duplicated for standard output. If set to null standard output will be connected to
/dev/null, i.e. everything written to it will be lost. If set to tty standard output
will be connected 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.
syslog connects standard output to the syslog(3) system syslog service. kmsg connects
it with the kernel log buffer which is accessible via dmesg(1). journal connects it
with the journal which is accessible via journalctl(1) (Note that everything that is
written to syslog or kmsg is implicitly stored in the journal as well, those options
are hence supersets of this one). syslog+console, journal+console and kmsg+console
work similarly but copy the output to the system console as well. socket connects
standard output to a socket from socket activation, semantics are similar to the
respective option of StandardInput=. This setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which defaults to journal.

StandardError=
Controls where file descriptor 2 (STDERR) of the executed processes is connected to.
The available options are identical to those of StandardOutput=, with one exception:
if set to inherit the file descriptor used for standard output is duplicated for
standard error. This setting defaults to the value set with DefaultStandardError= in
systemd-system.conf(5), which defaults to inherit.

TTYPath=
Sets the terminal device node to use if standard input, output or stderr 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.

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.

SyslogIdentifier=
Sets the process name to prefix log lines sent to syslog 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 syslog or kmsg.

SyslogFacility=
Sets the syslog facility to use when logging to syslog. 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 syslog. Defaults to
daemon.

SyslogLevel=
Default syslog level to use when logging to syslog 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 syslog or
kmsg. Note that individual lines output by the daemon might 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
syslog, kmsg or journal, log lines written by the executed process that are prefixed
with a log level will be passed on to syslog 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. For details about this prefixing see sd-daemon(3).
Defaults to true.

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.

LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=,
LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=,
LimitNICE=, LimitRTPRIO=, LimitRTTIME=
These settings control various resource limits for executed processes. See
setrlimit(2) for details. Use the string infinity to configure no limit on a specific
resource.

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. If not set no PAM session will be opened for the
executed processes. See pam(8) for details.

TCPWrapName=
If this is a socket-activated service this sets the tcpwrap service name to check the
permission for the current connection with. This is only useful in conjunction with
socket-activated services, and stream sockets (TCP) in particular. It has no effect on
other socket types (e.g. datagram/UDP) and on processes unrelated to socket-based
activation. If the tcpwrap verification fails daemon start-up will fail and the
connection is terminated. See tcpd(8) for details. Note that this option may be used
to do access control checks only. Shell commands and commands described in
hosts_options(5) are not supported.

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 as read by cap_from_name(3), 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, on top of what Capabilities= does. 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. 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.

SecureBits=
Controls the secure bits set for the executed process. See capabilities(7) for
details. Takes a list of strings: keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot and/or 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.

Capabilities=
Controls the capabilities(7) set for the executed process. Take a capability string
describing the effective, permitted and inherited capability sets as documented in
cap_from_text(3). Note that these capability sets are usually influenced by the
capabilities attached to the executed file. Due to that CapabilityBoundingSet= is
probably the much more useful setting.

ControlGroup=
Controls the control groups the executed processes shall be made members of. Takes a
space-separated list of cgroup identifiers. A cgroup identifier is formatted like
cpu:/foo/bar, where "cpu" indicates the kernel control group controller used, and
/foo/bar is the control group path. The controller name and ":" may be omitted in
which case the named systemd control group hierarchy is implied. Alternatively, the
path and ":" may be omitted, in which case the default control group path for this
unit is implied.

This option may be used to place executed processes in arbitrary groups in arbitrary
hierarchies -- which may then be externally configured with additional execution
limits. By default systemd will place all executed processes in separate per-unit
control groups (named after the unit) in the systemd named hierarchy. This option is
primarily intended to place executed processes in specific paths in specific kernel
controller hierarchies. It is not recommended to manipulate the service control group
path in the private systemd named hierarchy (i.e. name=systemd), and doing this might
result in undefined behaviour. For details about control groups see cgroups.txt[2].

This option may appear more than once, in which case the list of control group
assignments is merged. If the same hierarchy gets two different paths assigned only
the later setting will take effect. If the empty string is assigned to this option the
list of control group assignments is reset, all previous assignments will have no
effect.

Note that the list of control group assignments of a unit is extended implicitly based
on the settings of DefaultControllers= of systemd-system.conf(5), but a unit's
ControlGroup= setting for a specific controller takes precedence.

ControlGroupModify=
Takes a boolean argument. If true, the control groups created for this unit will be
owned by the user specified with User= (and the appropriate group), and he/she can
create subgroups as well as add processes to the group.

ControlGroupPersistent=
Takes a boolean argument. If true, the control groups created for this unit will be
marked to be persistent, i.e. systemd will not remove them when stopping the unit. The
default is false, meaning that the control groups will be removed when the unit is
stopped. For details about the semantics of this logic see PaxControlGroups[3].

ControlGroupAttribute=
Set a specific control group attribute for executed processes, and (if needed) add the
executed processes to a cgroup in the hierarchy of the controller the attribute
belongs to. Takes two space-separated arguments: the attribute name (syntax is
cpu.shares where cpu refers to a specific controller and shares to the attribute
name), and the attribute value. Example: ControlGroupAttribute=cpu.shares 512. If this
option is used for an attribute that belongs to a kernel controller hierarchy the unit
is not already configured to be added to (for example via the ControlGroup= option)
then the unit will be added to the controller and the default unit cgroup path is
implied. Thus, using ControlGroupAttribute= is in most cases sufficient to make use of
control group enforcements, explicit ControlGroup= are only necessary in case the
implied default control group path for a service is not desirable. For details about
control group attributes see cgroups.txt[2]. This option may appear more than once, in
order to set multiple control group attributes. If this option is used multiple times
for the same cgroup attribute only the later setting takes effect. If the empty string
is assigned to this option the list of attributes is reset, all previous cgroup
attribute settings have no effect, including those done with CPUShares=, MemoryLimit=,
MemorySoftLimit, DeviceAllow=, DeviceDeny=, BlockIOWeight=, BlockIOReadBandwidth=,
BlockIOWriteBandwidth=.

CPUShares=
Assign the specified overall CPU time shares to the processes executed. Takes an
integer value. This controls the cpu.shares control group attribute, which defaults to
1024. For details about this control group attribute see sched-design-CFS.txt[4].

MemoryLimit=, MemorySoftLimit=
Limit the overall memory usage of the executed processes to a certain size. Takes a
memory size in bytes. If the value is suffixed with K, M, G or T the specified memory
size is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (to the base 1024),
respectively. This controls the memory.limit_in_bytes and memory.soft_limit_in_bytes
control group attributes. For details about these control group attributes see
memory.txt[5].

DeviceAllow=, DeviceDeny=
Control access to specific device nodes by the executed processes. Takes two space
separated strings: a device node path (such as /dev/null) followed by a combination of
r, w, m to control reading, writing, or creating of the specific device node by the
unit, respectively. This controls the devices.allow and devices.deny control group
attributes. For details about these control group attributes see devices.txt[6].

BlockIOWeight=
Set the default or per-device overall block IO weight value for the executed
processes. Takes either a single weight value (between 10 and 1000) to set the default
block IO weight, or a space separated pair of a file path and a weight value to
specify the device specific weight value (Example: "/dev/sda 500"). The file path may
be specified as path to a block device node or as any other file in which case the
backing block device of the file system of the file is determined. This controls the
blkio.weight and blkio.weight_device control group attributes, which default to 1000.
Use this option multiple times to set weights for multiple devices. For details about
these control group attributes see blkio-controller.txt[7].

BlockIOReadBandwidth=, BlockIOWriteBandwidth=
Set the per-device overall block IO bandwidth limit for the executed processes. Takes
a space separated pair of a file path and a bandwidth value (in bytes per second) to
specify the device specific bandwidth. The file path may be specified as path to a
block device node or as any other file in which case the backing block device of the
file system of the file is determined. If the bandwidth is suffixed with K, M, G, or T
the specified bandwidth is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes,
respectively (Example: "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This
controls the blkio.read_bps_device and blkio.write_bps_device control group
attributes. Use this option multiple times to set bandwidth limits for multiple
devices. For details about these control group attributes see blkio-controller.txt[7].

ReadWriteDirectories=, ReadOnlyDirectories=, InaccessibleDirectories=
Sets up a new file-system name space for executed processes. These options may be used
to limit access a process might have to the main file-system hierarchy. Each setting
takes a space-separated list of absolute directory paths. Directories listed in
ReadWriteDirectories= are accessible from within the namespace with the same access
rights as from outside. Directories listed in ReadOnlyDirectories= are accessible for
reading only, writing will be refused even if the usual file access controls would
permit this. Directories listed in InaccessibleDirectories= will be made inaccessible
for processes inside the namespace. Note that restricting access with these options
does not extend to submounts of a directory. You must list submounts separately in
these settings to ensure the same limited access. These options may be specified more
than once in which case all directories 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.

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. All temporary data created by service will be removed after
service is stopped. Defaults to false.

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 securely
turn off network access by the executed process. Defaults to false.

MountFlags=
Takes a mount propagation flag: shared, slave or private, which control whether the
file system namespace set up for this unit's processes will receive or propagate new
mounts. See mount(2) for details. Default to shared.

UtmpIdentifier=
Takes a four character identifier string for an utmp/wtmp entry for this service. This
should only be set for services such as getty implementations where utmp/wtmp entries
must be created and cleared before and after execution. 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.

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

NoNewPrivileges=
Takes a boolean argument. If true ensures that the service process and all its
children can never gain new privileges. This option is more powerful than the
respective secure bits flags (see above), as it also prohibits UID changes of any
kind. This is the simplest, most effective way to ensure that a process and its
children can never elevate privileges again.

SystemCallFilter=
Takes a space separated list of system call names. If this setting is used all system
calls executed by the unit process except for the listed ones will result in immediate
process termination with the SIGSYS signal (whitelisting). If the first character of
the list is ~ the effect is inverted: only the listed system calls will result in
immediate process termination (blacklisting). If this option is used
NoNewPrivileges=yes is implied. 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, rt_sigreturn, sigreturn, exit_group,
exit system calls are implicitly whitelisted and don't 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.

NOTES

        1. proc.txt
           http://www.kernel.org/doc/Documentation/filesystems/proc.txt

        2. cgroups.txt
           http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

        3. PaxControlGroups
           http://www.freedesktop.org/wiki/Software/systemd/PaxControlGroups

        4. sched-design-CFS.txt
           http://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt

        5. memory.txt
           http://www.kernel.org/doc/Documentation/cgroups/memory.txt

        6. devices.txt
           http://www.kernel.org/doc/Documentation/cgroups/devices.txt

        7. blkio-controller.txt
           http://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

SEE ALSO

NOTES