Section: systemd.exec (5)
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systemd.exec - Execution environment configuration
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
for the common options of all unit configuration files, and
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.
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.
Takes an absolute directory path. Sets the root directory for executed processes, with the
system call. If this is used, it must be ensured that the process and all its auxiliary files are available in the
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.
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.
Sets the default nice level (scheduling priority) for executed processes. Takes an integer between -20 (highest priority) and 19 (lowest priority). See
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
Sets the IO scheduling class for executed processes. Takes an integer between 0 and 3 or one of the strings
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
Sets the CPU scheduling policy for executed processes. Takes one of
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
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
for details. Defaults to false.
Controls the CPU affinity of the executed processes. Takes a space-separated list of CPU indices. 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
Controls the file mode creation mask. Takes an access mode in octal notation. See
for details. Defaults to 0022.
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, however, specifier expansion is possible. The $ character has no special meaning. If you need to assign a value containing spaces to a variable, use double quotes (") for the assignment.
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
gives three variables
with the values
"$word 5 6".
for details about environment variables.
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 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). 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.
Controls where file descriptor 0 (STDIN) of the executed processes is connected to. Takes one of
is selected, standard input will be connected to
/dev/null, i.e. all read attempts by the process will result in immediate EOF. If
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.
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.
is similar to
but if the terminal already has a controlling process start-up of the executed process fails. The
option is only valid in socket-activated services, and only when the socket configuration file (see
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
daemon. This setting defaults to
Controls where file descriptor 1 (STDOUT) of the executed processes is connected to. Takes one of
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.
connects standard output to the
system syslog service.
connects it with the kernel log buffer which is accessible via
connects it with the journal which is accessible via
(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).
work similarly but copy the output to the system console as well.
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
systemd-system.conf(5), which defaults to
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
the file descriptor used for standard output is duplicated for standard error. This setting defaults to the value set with
systemd-system.conf(5), which defaults to
Sets the terminal device node to use if standard input, output, or error are connected to a TTY (see above). Defaults to
Reset the terminal device specified with
before and after execution. Defaults to
Disconnect all clients which have opened the terminal device specified with
before and after execution. Defaults to
If the terminal device specified with
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
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
are set to
Sets the syslog facility to use when logging to syslog. One of
for details. This option is only useful when
are set to
syslog. Defaults to
Default syslog level to use when logging to syslog or the kernel log buffer. One of
for details. This option is only useful when
are set to
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
Takes a boolean argument. If true and
are set to
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.
Sets the timer slack in nanoseconds for the executed processes. The timer slack controls the accuracy of wake-ups triggered by timers. See
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
for details. Use the string
to configure no limit on a specific resource.
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
setting. If not set, no PAM session will be opened for the executed processes. See
Controls which capabilities to include in the capability bounding set for the executed process. See
for details. Takes a whitespace-separated list of capability names as read by
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
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.
Controls the secure bits set for the executed process. See
for details. Takes a list of strings:
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.
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 (and filtered) by the capabilities attached to the executed file. Due to that
is probably the much more useful setting.
ReadWriteDirectories=, ReadOnlyDirectories=, InaccessibleDirectories=
Sets up a new file system namespace 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
are accessible from within the namespace with the same access rights as from outside. Directories listed in
are accessible for reading only, writing will be refused even if the usual file access controls would permit this. Directories listed in
will be made inaccessible for processes inside the namespace. Note that restricting access with these options does not extend to submounts of a directory that are created later on. 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.
may be prefixed with
"-", in which case they will be ignored when they do not exist. 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.
Takes a boolean argument. If true, sets up a new file system namespace for the executed processes and mounts private
directories inside it that is 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
impossible. If this is enabled, 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
namespace by using the
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.
Takes a boolean argument. If true, sets up a new /dev namespace for the executed processes and only adds API pseudo devices such as
(as well as the pseudo TTY subsystem) to it, but no physical devices such as
/dev/sda. This is useful to securely turn off physical device access by the executed process. Defaults to false. Enabling this option will also remove
from the capability bounding set for the unit (see above), and set
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.
Takes a boolean argument. If true, sets up a new network namespace for the executed processes and configures only the loopback network device
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. It is possible to run two or more units within the same private network namespace by using the
for details. Note that this option will disconnect all socket families from the host, this includes AF_NETLINK and AF_UNIX. The latter has the effect that AF_UNIX sockets in the abstract socket namespace will become unavailable to the processes (however, those located in the file system will continue to be accessible).
Takes a boolean argument or
"full". If true, mounts the
directory read-only for processes invoked by this unit. If set to
directory is mounted read-only, too. This setting ensures that any modification of the vendor supplied operating system (and optionally its configuration) 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. Note however that processes retaining the CAP_SYS_ADMIN capability can undo the effect of this setting. This setting is hence particularly useful for daemons which have this capability removed, for example with
CapabilityBoundingSet=. Defaults to off.
Takes a boolean argument or
"read-only". If true, the directories
are made inaccessible and empty for processes invoked by this unit. If set to
"read-only", the two directores are made read-only instead. 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. Note however that processes retaining the CAP_SYS_ADMIN capability can undo the effect of this setting. This setting is hence particularly useful for daemons which have this capability removed, for example with
CapabilityBoundingSet=. Defaults to off.
Takes a mount propagation flag:
private, which control whether mounts in the file system namespace set up for this unit's processes will receive or propagate mounts or unmounts. See
for details. Defaults to
to ensure that mounts and unmounts are propagated from the host to the container and vice versa. Use
to run processes so that none of their mounts and unmounts will propagate to the host. Use
to also ensure that no mounts and unmounts from the host will propagate into the unit processes' namespace. Note that
means that file systems mounted on the host might stay mounted continously in the unit's namespace, and thus keep the device busy. Note that the file system namespace related options (PrivateTmp=,
ReadWriteDirectories=) require that mount and unmount propagation from the unit's file system namespace is disabled, and hence downgrade
Takes a four character identifier string for an utmp/wtmp entry for this service. This should only be set for services such as
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.
Set the SELinux security context of the executed process. If set, this will override the automated domain transition. However, the policy still needs to autorize the transition. This directive is ignored if SELinux is disabled. If prefixed by
"-", all errors will be ignored. See
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. This result in a non operation if AppArmor is not enabled. If prefixed by
"-", all errors will be ignored.
Takes a boolean argument. If true, causes
to be ignored in the executed process. Defaults to true because
generally is useful only in shell pipelines.
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.
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
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 running in user mode and this option is used,
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
system calls are implicitly whitelisted 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.
If you specify both types of this option (i.e. whitelisting and blacklisting), 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 a whitelisting of
write, and right after it add a blacklisting of
will be removed from the set.)
error number name to return when the system call filter configured with
is triggered, instead of terminating the process immediately. Takes an error name such as
EUCLEAN. When this setting is not used, or when the empty string is assigned, the process will be terminated immediately when the filter is triggered.
Takes a space separated list of architecture identifiers to include in the system call filter. The known architecture identifiers are
as well as the special identifier
native. Only system calls of the specified architectures will be permitted to processes of this unit. This is an effective way to disable compatibility with non-native architectures for processes, for example to prohibit execution of 32-bit x86 binaries on 64-bit x86-64 systems. The special
identifier implicitly maps to the native architecture of the system (or more strictly: to the architecture the system manager is compiled for). If running in user mode and this option is used,
is implied. Note that setting this option to a non-empty list implies that
is included too. By default, this option is set to the empty list, i.e. no architecture system call filtering is applied.
Restricts the set of socket address families accessible to the processes of this unit. Takes a space-separated list of address family names to whitelist, such as
AF_INET6. When prefixed with
the listed address families will be applied as blacklist, otherwise as whitelist. Note that this restricts access to the
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
(which creates connected AF_UNIX sockets only) are unaffected. Note that this option has no effect on 32-bit x86 and is ignored (but works correctly on x86-64). If running in user mode and this option is used,
is implied. By default, no restriction applies, all address families are accessible to processes. If assigned the empty string, any previous list changes are undone.
Use this option to limit exposure of processes to remote systems, in particular via exotic network protocols. Note that in most cases, the local
address family should be included in the configured whitelist as it is frequently used for local communication, including for
Controls which kernel architecture
shall report, when invoked by unit processes. Takes one of
x86-64. This 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.
Takes a list of directory names. If set, one or more directories by the specified names will be created below
(for system services) or below
(for user services) when the unit is started, and removed when the unit is stopped. The directories will have the access mode specified in
RuntimeDirectoryMode=, and will be owned by the user and group specified in
Group=. Use this to manage one or more runtime directories of the unit and bind their lifetime to the daemon runtime. The specified directory names must be relative, and may not include a
"/", i.e. must refer to simple directories to create or remove. This is particularly useful for unprivileged daemons that cannot create runtime directories in
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
ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
Processes started by the system are executed in a clean environment in which select variables listed below are set. System processes started by systemd do not inherit variables from PID 1, but processes started by user systemd instances inherit all environment variables from the user systemd instance.
Colon-separated list of directiories to use when launching executables. Systemd uses a fixed value of
Locale. Can be set in
or on the kernel command line (see
$USER, $LOGNAME, $HOME, $SHELL
User name (twice), home directory, and the login shell. The variables are set for the units that have
set, which includes user
The directory for volatile state. Set for the user
instance, and also in user sessions. See
$XDG_SESSION_ID, $XDG_SEAT, $XDG_VTNR
The identifier of the session, the seat name, and virtual terminal of the session. Set by
for login sessions.
will only be set when attached to a seat and a tty.
The PID of the units main process if it is known. This is only set for control processes as invoked by
The PID of the user
instance, set for processes spawned by it.
Information about file descriptors passed to a service for socket activation. See
Terminal type, set only for units connected to a terminal (StandardInput=tty,
Additional variables may be configured by the following means: for processes spawned in specific units, use the
options above; to specify variables globally, use
systemd-system.conf(5)) or the kernel option
systemd(1)). Additional variables may also be set through PAM, cf. pam_env(8).
- ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
- SEE ALSO