systemd.exec(5)

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:

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=

Added in version 250.

WorkingDirectory=

RootDirectory=

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

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

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

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

Example 1. Mounting logging sockets into root environment

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

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

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

RootImage=

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

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

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

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

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

Added in version 233.

RootImageOptions=

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=

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=

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=

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=

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=

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

The default policy for ExtensionImagePolicy= is:

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

Added in version 254.

MountAPIVFS=

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.

BindLogSockets=

This option is implied when LogNamespace= is used, when MountAPIVFS=yes, or when PrivateDevices=yes is used in conjunction with either RootDirectory= or RootImage=.

Added in version 257.

ProtectProc=

If the kernel does not 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=

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=

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

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

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

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

Added in version 233.

MountImages=

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=

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

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

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

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

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

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

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

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

Added in version 248.

ExtensionDirectories=

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

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

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

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

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

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

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

Added in version 251.

USER/GROUP IDENTITY#

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

User=, Group=

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=

Added in version 232.

SupplementaryGroups=

SetLoginEnvironment=

Added in version 255.

PAMName=

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=

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=

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=

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=

MANDATORY ACCESS CONTROL#

SELinuxContext=

Added in version 209.

AppArmorProfile=

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 210.

SmackProcessLabel=

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 "+".

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 218.

PROCESS PROPERTIES#

LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=, LimitRTTIME=

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 [email protected]. 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

UMask=

CoredumpFilter=

Example 2. Add DAX pages to the dump filter

CoredumpFilter=default private-dax shared-dax

Added in version 246.

KeyringMode=

Added in version 235.

OOMScoreAdjust=

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=

Personality=

Added in version 209.

IgnoreSIGPIPE=

SCHEDULING#

Nice=

CPUSchedulingPolicy=

CPUSchedulingPriority=

CPUSchedulingResetOnFork=

CPUAffinity=

NUMAPolicy=

Added in version 243.

NUMAMask=

Added in version 243.

IOSchedulingClass=

IOSchedulingPriority=

SANDBOXING#

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

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

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

ProtectSystem=

Note that if ProtectSystem= is set to "strict" and PrivateTmp= is enabled, then /tmp/ and /var/tmp/ will be writable.

Added in version 214.

ProtectHome=

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=

If DynamicUser= is used, and if the kernel version supports id-mapped mounts[7], the specified directories will be owned by "nobody" in the host namespace and will be mapped to (and will be owned by) the service's UID/GID in its own namespace. For backward compatibility, existing directories created without id-mapped mounts will be kept untouched.

Table 2. Automatic directory creation and environment variables

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 two more parameters, 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 third parameter is a flags field, and since v257 can take a value of ro to make the directory read only for the service. This is also supported for ConfigurationDirectory=. If multiple symlinks are set up, the directory will be read only if at least one is configured to be read only. To pass a flag without a destination symlink, the second parameter can be empty, for example:

ConfigurationDirectory=foo::ro

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=

Added in version 234.

RuntimeDirectoryPreserve=

Added in version 235.

TimeoutCleanSec=

Added in version 244.

ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths=, NoExecPaths=

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=

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=

This setting is useful to secure access to temporary files of the process, but makes sharing between processes via /tmp/ or /var/tmp/ impossible. If not set to "disconnected", 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. If set to "true" (as opposed to "disconnected"), this has the side effect of adding Requires= and After= dependencies on all mount units necessary to access /tmp/ and /var/tmp/ on the host. 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=

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=

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=

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=

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=

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=

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

Added in version 254.

PrivatePIDs=

PrivatePIDs= is only supported for service units. This setting is not supported with Type=forking since the kernel will kill all processes in the PID namespace if the init process terminates.

This setting will be ignored if the kernel does not support PID namespaces.

Note unprivileged user services (i.e. a service run by the per-user instance of the service manager) will fail with PrivatePIDs=yes if /proc/ is masked (i.e. /proc/kmsg is over-mounted with tmpfs like systemd-nspawn(1) does). This is due to a kernel restriction not allowing unprivileged user namespaces to mount a less restrictive instance of /proc/.

Added in version 257.

PrivateUsers=

If the parameter is "identity", user namespacing is set up with an identity mapping for the first 65536 UIDs/GIDs. Any UIDs/GIDs above 65536 will be mapped to the "nobody" user and group, respectively. While this does not provide UID/GID isolation, since all UIDs/GIDs are chosen identically it does provide process capability isolation, and hence is often a good choice if proper user namespacing with distinct UID maps is not appropriate.

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.

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=

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=

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=

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=

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=

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=

Except for container managers no services should require write access to the control groups hierarchies; it is hence recommended to set ProtectControlGroups= to true or "strict" for most services. For this setting the same restrictions regarding mount propagation and privileges apply as for ReadOnlyPaths= and related settings, see above.

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=

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.

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) or the io_uring(7) functions, are not affected. Thus, it is recommended to combined this setting with SystemCallFilter=@service, to only allow a limited subset of system calls.

Note that this option is limited to some ABIs, in particular x86-64, but currently has no effect on 32-bit x86, s390, s390x, mips, mips-le, ppc, ppc-le, ppc64, or ppc64-le, and is ignored. 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 211.

RestrictFileSystems=

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

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=

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=

Added in version 235.

MemoryDenyWriteExecute=

Added in version 231.

RestrictRealtime=

Added in version 231.

RestrictSUIDSGID=

Added in version 242.

RemoveIPC=

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=

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

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

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

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

Added in version 239.

MountFlags=

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 will not 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=

Commands prefixed with "+" are not subject to filtering. 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.

The default action when a system call is denied is to terminate the processes with a SIGSYS signal. This can changed using SystemCallErrorNumber=, see below. In addition, deny-listed system calls and system call groups may optionally be suffixed with a colon (":") and an argument in the same format as SystemCallErrorNumber=, to take this action when the matching system call is made. This takes precedence over the action specified in SystemCallErrorNumber=.

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 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 allow 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 groups of system calls are provided. A group starts with "@" character, followed by name of the set.

Table 4. Currently predefined system call sets

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=

Added in version 209.

SystemCallArchitectures=

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=

Added in version 247.

ENVIRONMENT#

Environment=

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=

In the file, an unquoted value after the "=" is parsed with the same backslash-escape rules as POSIX shell unquoted text[12], 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[13]. 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[14]. 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=

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=

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=

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=

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. Note: if a unit tries to print multiple lines to a TTY during bootup or shutdown, then there's a chance that those lines will be broken up by status messages. SetShowStatus() can be used to prevent this problem. See org.freedesktop.systemd1(5) for details.

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 does not exist yet using privileges of the user executing the systemd process) for writing at the beginning of the file, but without truncating it. If standard input and output are directed to the same file path, it is opened only once — for reading as well as writing — and duplicated. This is particularly useful when the specified path refers to an AF_UNIX socket in the file system, as in that case only a single stream connection is created for both input and output.

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

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

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

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

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

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

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

StandardError=

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=

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[15]. 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 \
\n
                  IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \
\n
                  dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \
\n
                  J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \
\n
                  dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \
\n
                  ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \
\n
                  eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK
...

Added in version 236.

LogLevelMax=

Added in version 236.

LogExtraFields=

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

Added in version 236.

LogRateLimitIntervalSec=, LogRateLimitBurst=

Added in version 240.

LogFilterPatterns=

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

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

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

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

Added in version 253.

LogNamespace=

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 [email protected] 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=

SyslogFacility=

SyslogLevel=

SyslogLevelPrefix=

TTYPath=

TTYReset=

TTYVHangup=

TTYColumns=, TTYRows=

Added in version 250.

TTYVTDisallocate=

CREDENTIALS#

LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]

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

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

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

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

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

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

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

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

The credential files/IPC sockets must be accessible to the service manager, but do not 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[16] documentation for details about the former. For the latter, pass DMI/SMBIOS[17] 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[18] 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 NULRANDOM "/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[19] documentation.

Added in version 247.

ImportCredential=GLOB

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.

Optionally, the credential name or glob may be followed by a colon followed by a rename pattern. If specified, all credentials matching the credential name or glob are renamed according to the given pattern. For example, if "ImportCredential=my.original.cred:my.renamed.cred" is specified, the service manager will read the "my.original.cred" credential and make it available as the "my.renamed.cred" credential to the service. Similarly, if "ImportCredential=my.original.*:my.renamed." is specified, the service manager will read all credentials starting with "my.original." and make them available as "my.renamed.xxx" to the service.

If ImportCredential= is specified multiple times and multiple credentials end up with the same name after renaming, the first one is kept and later ones are dropped.

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 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=

UtmpMode=

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:

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

Added in version 208.

$LANG

Added in version 208.

$USER, $LOGNAME, $HOME, $SHELL

Added in version 208.

$INVOCATION_ID

Added in version 232.

$XDG_RUNTIME_DIR

Added in version 208.

$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY, $LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY

Added in version 244.

$CREDENTIALS_DIRECTORY

Added in version 247.

$MAINPID

Added in version 209.

$MANAGERPID

Added in version 208.

$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES

Added in version 208.

$NOTIFY_SOCKET

Added in version 229.

$WATCHDOG_PID, $WATCHDOG_USEC

Added in version 229.

$SYSTEMD_EXEC_PID

Added in version 248.

$TERM

Added in version 209.

$LOG_NAMESPACE

Added in version 246.

$JOURNAL_STREAM

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

Table 5. Defined $SERVICE_RESULT values

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

Table 6. Summary of possible service result variable values

Added in version 232.

$MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE, $MONITOR_EXIT_STATUS, $MONITOR_INVOCATION_ID, $MONITOR_UNIT

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 specify the same unit as their OnFailure= or OnSuccess= handler, those variables will 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

Added in version 242.

$REMOTE_ADDR, $REMOTE_PORT

For IPv4 and IPv6 connections, $REMOTE_ADDR contains the IP address, and $REMOTE_PORT contains the port number of the remote peer.

For AF_UNIX socket connections, $REMOTE_ADDR contains either the remote socket's file system path starting with a slash ("/"), its address in the abstract namespace starting with an at symbol ("@"), or is unset in case of an unnamed socket. $REMOTE_PORT is not set for AF_UNIX sockets.

Added in version 220.

$TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC, $TRIGGER_TIMER_MONOTONIC_USEC

Added in version 252.

$MEMORY_PRESSURE_WATCH, $MEMORY_PRESSURE_WRITE

Added in version 254.

$FDSTORE

Added in version 254.

$DEBUG_INVOCATION

Added in version 257.

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

The following service exit codes are defined by the LSB specification[21].

Table 8. LSB service exit codes

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

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

Table 10. BSD exit codes

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

2.

The /proc Filesystem

3.

User/Group Name Syntax

4.

No New Privileges Flag

5.

JSON User Record

6.

The /proc Filesystem

7.

id-mapped mounts

8.

Kernel Samepage Merging

9.

unicode scalar values

10.

unicode noncharacters

11.

unicode byte order mark

12.

POSIX shell unquoted text

13.

POSIX shell single-quoted text

14.

POSIX shell double-quoted text

15.

Base64

16.

Container Interface

17.

DMI/SMBIOS

18.

qemu

19.

System and Service Credentials

20.

Memory Pressure Handling

21.

LSB specification