systemd.execsystemdsystemd.exec5systemd.execExecution environment configurationservice.service,
socket.socket,
mount.mount,
swap.swapDescriptionUnit 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.unit5 for the common
options of all unit configuration files, and
systemd.service5,
systemd.socket5,
systemd.swap5, and
systemd.mount5 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-control5.
Those options complement options listed here.Implicit DependenciesA few execution parameters result in additional, automatic dependencies to be added:Units with WorkingDirectory=, RootDirectory=,
RootImage=, RuntimeDirectory=, StateDirectory=,
CacheDirectory=, LogsDirectory= or
ConfigurationDirectory= set automatically gain dependencies of type
Requires= and After= on all mount units required to access the specified
paths. This is equivalent to having them listed explicitly in
RequiresMountsFor=.Similarly, units with PrivateTmp= enabled automatically get mount
unit dependencies for all mounts required to access /tmp/ and
/var/tmp/. They will also gain an automatic After= dependency
on
systemd-tmpfiles-setup.service8.
Units whose standard output or error output is connected to or
(or their combinations with console output, see below) automatically acquire
dependencies of type After= on
systemd-journald.socket.Units using LogNamespace= will automatically gain ordering and
requirement dependencies on the two socket units associated with
systemd-journald@.service instances.PathsThe 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.WorkingDirectory=Takes a directory path relative to the service's root directory specified by
RootDirectory=, or the special value ~. Sets the working directory for
executed processes. If set to ~, the home directory of the user specified in
User= is used. If not set, defaults to the root directory when systemd is running as a
system instance and the respective user's home directory if run as user. If the setting is prefixed with the
- character, a missing working directory is not considered fatal. If
RootDirectory=/RootImage= is not set, then
WorkingDirectory= is relative to the root of the system running the service manager. Note
that setting this parameter might result in additional dependencies to be added to the unit (see
above).RootDirectory=Takes a directory path relative to the host's root directory (i.e. the root of the system
running the service manager). Sets the root directory for executed processes, with the chroot2 system
call. If this is used, it must be ensured that the process binary and all its auxiliary files are available in
the chroot() jail. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).The MountAPIVFS= and PrivateUsers= settings are particularly useful
in conjunction with RootDirectory=. For details, see below.RootImage=Takes a path to a block device node or regular file as argument. This call is similar
to RootDirectory= however mounts a file system hierarchy from a block device node
or loopback file instead of a directory. The device node or file system image file needs to contain a
file system without a partition table, or a file system within an MBR/MS-DOS or GPT partition table
with only a single Linux-compatible partition, or a set of file systems within a GPT partition table
that follows the Discoverable Partitions
Specification.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-control5
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.RootImageOptions=Takes a comma-separated list of mount options that will be used on disk images specified by
RootImage=. Optionally a partition name can be prefixed, followed by colon, in
case the image has multiple partitions, otherwise partition name root is implied.
Options for multiple partitions can be specified in a single line with space separators. Assigning an empty
string removes previous assignments. Duplicated options are ignored. For a list of valid mount options, please
refer to
mount8.
Valid partition names follow the Discoverable
Partitions Specification.
RootHash=Takes a data integrity (dm-verity) root hash specified in hexadecimal, or the path to a file
containing a root hash in ASCII hexadecimal format. This option enables data integrity checks using dm-verity,
if the used image contains the appropriate integrity data (see above) or if RootVerity= is used.
The specified hash must match the root hash of integrity data, and is usually at least 256 bits (and hence 64
formatted hexadecimal characters) long (in case of SHA256 for example). If this option is not specified, but
the image file carries the user.verity.roothash extended file attribute (see xattr7), then the root
hash is read from it, also as formatted hexadecimal characters. If the extended file attribute is not found (or
is not supported by the underlying file system), but a file with the .roothash suffix is
found next to the image file, bearing otherwise the same name (except if the image has the
.raw suffix, in which case the root hash file must not have it in its name), the root hash
is read from it and automatically used, also as formatted hexadecimal characters.If the disk image contains a separate /usr/ partition it may also be
Verity protected, in which case the root hash may configured via an extended attribute
user.verity.usrhash or a .usrhash file adjacent to the disk
image. There's currently no option to configure the root hash for the /usr/ file
system via the unit file directly.RootHashSignature=Takes a PKCS7 signature of the RootHash= option as a path to a
DER-encoded signature file, or as an ASCII base64 string encoding of a DER-encoded signature prefixed
by base64:. The dm-verity volume will only be opened if the signature of the root
hash is valid and signed by a public key present in the kernel keyring. If this option is not
specified, but a file with the .roothash.p7s suffix is found next to the image
file, bearing otherwise the same name (except if the image has the .raw suffix,
in which case the signature file must not have it in its name), the signature is read from it and
automatically used.If the disk image contains a separate /usr/ partition it may also be
Verity protected, in which case the signature for the root hash may configured via a
.usrhash.p7s file adjacent to the disk image. There's currently no option to
configure the root hash signature for the /usr/ via the unit file
directly.RootVerity=Takes the path to a data integrity (dm-verity) file. This option enables data integrity checks
using dm-verity, if RootImage= is used and a root-hash is passed and if the used image itself
does not contains the integrity data. The integrity data must be matched by the root hash. If this option is not
specified, but a file with the .verity suffix is found next to the image file, bearing otherwise
the same name (except if the image has the .raw suffix, in which case the verity data file must
not have it in its name), the verity data is read from it and automatically used.This option is supported only for disk images that contain a single file system, without an
enveloping partition table. Images that contain a GPT partition table should instead include both
root file system and matching Verity data in the same image, implementing the Discoverable Partition Specification.MountAPIVFS=Takes a boolean argument. If on, a private mount namespace for the unit's processes is created
and the API file systems /proc/, /sys/, and /dev/
are mounted inside of it, unless they are already mounted. Note that this option has no effect unless used in
conjunction with RootDirectory=/RootImage= as these three mounts are
generally mounted in the host anyway, and unless the root directory is changed, the private mount namespace
will be a 1:1 copy of the host's, and include these three mounts. Note that the /dev/ file
system of the host is bind mounted if this option is used without PrivateDevices=. To run
the service with a private, minimal version of /dev/, combine this option with
PrivateDevices=.ProtectProc=Takes one of noaccess, invisible,
ptraceable or default (which it defaults to). When set, this
controls the hidepid= mount option of the procfs instance for
the unit that controls which directories with process metainformation
(/proc/PID) are visible and accessible: when set to
noaccess the ability to access most of other users' process metadata in
/proc/ is taken away for processes of the service. When set to
invisible processes owned by other users are hidden from
/proc/. If ptraceable all processes that cannot be
ptrace()'ed by a process are hidden to it. If default no
restrictions on /proc/ access or visibility are made. For further details see
The /proc
Filesystem. It is generally recommended to run most system services with this option set to
invisible. This option is implemented via file system namespacing, and thus cannot
be used with services that shall be able to install mount points in the host file system
hierarchy. It also cannot be used for services that need to access metainformation about other users'
processes. This option implies MountAPIVFS=.If the kernel doesn't support per-mount point 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.ProcSubset=Takes one of all (the default) and pid. If
the latter all files and directories not directly associated with process management and introspection
are made invisible in the /proc/ file system configured for the unit's
processes. This controls the subset= mount option of the procfs
instance for the unit. For further details see The /proc
Filesystem. Note that Linux exposes various kernel APIs via /proc/,
which are made unavailable with this setting. Since these APIs are used frequently this option is
useful only in a few, specific cases, and is not suitable for most non-trivial programs.Much like ProtectProc= above, this is implemented via file system mount
namespacing, and hence the same restrictions apply: it is only available to system services, it
disables mount propagation to the host mount table, and it implies
MountAPIVFS=. Also, like ProtectProc= this setting is gracefully
disabled if the used kernel does not support the subset= mount option of
procfs.BindPaths=BindReadOnlyPaths=Configures unit-specific bind mounts. A bind mount makes a particular file or directory
available at an additional place in the unit's view of the file system. Any bind mounts created with this
option are specific to the unit, and are not visible in the host's mount table. This option expects a
whitespace separated list of bind mount definitions. Each definition consists of a colon-separated triple of
source path, destination path and option string, where the latter two are optional. If only a source path is
specified the source and destination is taken to be the same. The option string may be either
rbind or norbind for configuring a recursive or non-recursive bind
mount. If the destination path is omitted, the option string must be omitted too.
Each bind mount definition may be prefixed with -, in which case it will be ignored
when its source path does not exist.BindPaths= creates regular writable bind mounts (unless the source file system mount
is already marked read-only), while BindReadOnlyPaths= creates read-only bind mounts. These
settings may be used more than once, each usage appends to the unit's list of bind mounts. If the empty string
is assigned to either of these two options the entire list of bind mounts defined prior to this is reset. Note
that in this case both read-only and regular bind mounts are reset, regardless which of the two settings is
used.This option is particularly useful when RootDirectory=/RootImage=
is used. In this case the source path refers to a path on the host file system, while the destination path
refers to a path below the root directory of the unit.Note that the destination directory must exist or systemd must be able to create it. Thus, it
is not possible to use those options for mount points nested underneath paths specified in
InaccessiblePaths=, or under /home/ and other protected
directories if ProtectHome=yes is
specified. TemporaryFileSystem= with :ro or
ProtectHome=tmpfs should be used instead.MountImages=This setting is similar to RootImage= in that it mounts a file
system hierarchy from a block device node or loopback file, but the destination directory can be
specified as well as mount options. This option expects a whitespace separated list of mount
definitions. Each definition consists of a colon-separated tuple of source path and destination
definitions, optionally followed by another colon and a list of mount options.Mount options may be defined as a single comma-separated list of options, in which case they
will be implicitly applied to the root partition on the image, or a series of colon-separated tuples
of partition name and mount options. Valid partition names and mount options are the same as for
RootImageOptions= setting described above.Each mount definition may be prefixed with -, in which case it will be
ignored when its source path does not exist. The source argument is a path to a block device node or
regular file. If source or destination contain a :, it needs to be escaped as
\:. The device node or file system image file needs to follow the same rules as
specified for RootImage=. Any mounts created with this option are specific to the
unit, and are not visible in the host's mount table.These settings may be used more than once, each usage appends to the unit's list of mount
paths. If the empty string is assigned, the entire list of mount paths defined prior to this is
reset.Note that the destination directory must exist or systemd must be able to create it. Thus, it
is not possible to use those options for mount points nested underneath paths specified in
InaccessiblePaths=, or under /home/ and other protected
directories if ProtectHome=yes is specified.When DevicePolicy= is set to closed or
strict, or set to auto and DeviceAllow= is
set, then this setting adds /dev/loop-control with rw mode,
block-loop and block-blkext with rwm mode
to DeviceAllow=. See
systemd.resource-control5
for the details about DevicePolicy= or DeviceAllow=. Also, see
PrivateDevices= below, as it may change the setting of
DevicePolicy=.CredentialsUser=Group=Set the UNIX user or group that the processes are executed as, respectively. Takes a single
user or group name, or a numeric ID as argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root user (services managed by root's instance of
systemd --user), the default is root, but User= may be
used to specify a different user. For user services of any other user, switching user identity is not
permitted, hence the only valid setting is the same user the user's service manager is running as. If no group
is set, the default group of the user is used. This setting does not affect commands whose command line is
prefixed with +.Note that this enforces only weak restrictions on the user/group name syntax, but will generate
warnings in many cases where user/group names do not adhere to the following rules: the specified
name should consist only of the characters a-z, A-Z, 0-9, _ and
-, except for the first character which must be one of a-z, A-Z and
_ (i.e. digits and - are not permitted as first character). The
user/group name must have at least one character, and at most 31. These restrictions are made in
order to avoid ambiguities and to ensure user/group names and unit files remain portable among Linux
systems. For further details on the names accepted and the names warned about see User/Group Name Syntax.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.d5
facility, which is applied at boot or package install time. If the user does not exist by then
program invocation will fail.If the User= setting is used the supplementary group list is initialized
from the specified user's default group list, as defined in the system's user and group
database. Additional groups may be configured through the SupplementaryGroups=
setting (see below).DynamicUser=Takes a boolean parameter. If set, a UNIX user and group pair is allocated
dynamically when the unit is started, and released as soon as it is stopped. The user and group will
not be added to /etc/passwd or /etc/group, but are managed
transiently during runtime. The
nss-systemd8 glibc
NSS module provides integration of these dynamic users/groups into the system's user and group
databases. The user and group name to use may be configured via User= and
Group= (see above). If these options are not used and dynamic user/group
allocation is enabled for a unit, the name of the dynamic user/group is implicitly derived from the
unit name. If the unit name without the type suffix qualifies as valid user name it is used directly,
otherwise a name incorporating a hash of it is used. If a statically allocated user or group of the
configured name already exists, it is used and no dynamic user/group is allocated. Note that if
User= is specified and the static group with the name exists, then it is required
that the static user with the name already exists. Similarly, if Group= is
specified and the static user with the name exists, then it is required that the static group with
the name already exists. Dynamic users/groups are allocated from the UID/GID range 61184…65519. It is
recommended to avoid this range for regular system or login users. At any point in time each UID/GID
from this range is only assigned to zero or one dynamically allocated users/groups in use. However,
UID/GIDs are recycled after a unit is terminated. Care should be taken that any processes running as
part of a unit for which dynamic users/groups are enabled do not leave files or directories owned by
these users/groups around, as a different unit might get the same UID/GID assigned later on, and thus
gain access to these files or directories. If DynamicUser= is enabled,
RemoveIPC= and PrivateTmp= are implied (and cannot be turned
off). This ensures that the lifetime of IPC objects and temporary files created by the executed
processes is bound to the runtime of the service, and hence the lifetime of the dynamic
user/group. Since /tmp/ and /var/tmp/ are usually the only
world-writable directories on a system this ensures that a unit making use of dynamic user/group
allocation cannot leave files around after unit termination. Furthermore
NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled
(and cannot be disabled), to ensure that processes invoked cannot take benefit or create SUID/SGID
files or directories. Moreover ProtectSystem=strict and
ProtectHome=read-only are implied, thus prohibiting the service to write to
arbitrary file system locations. In order to allow the service to write to certain directories, they
have to be allow-listed using ReadWritePaths=, but care must be taken so that
UID/GID recycling doesn't create security issues involving files created by the service. Use
RuntimeDirectory= (see below) in order to assign a writable runtime directory to a
service, owned by the dynamic user/group and removed automatically when the unit is terminated. Use
StateDirectory=, CacheDirectory= and
LogsDirectory= in order to assign a set of writable directories for specific
purposes to the service in a way that they are protected from vulnerabilities due to UID reuse (see
below). If this option is enabled, care should be taken that the unit's processes do not get access
to directories outside of these explicitly configured and managed ones. Specifically, do not use
BindPaths= and be careful with AF_UNIX file descriptor
passing for directory file descriptors, as this would permit processes to create files or directories
owned by the dynamic user/group that are not subject to the lifecycle and access guarantees of the
service. Defaults to off.SupplementaryGroups=Sets the supplementary Unix groups the processes are executed as. This takes a space-separated
list of group names or IDs. This option may be specified more than once, in which case all listed groups are
set as supplementary groups. When the empty string is assigned, the list of supplementary groups is reset, and
all assignments prior to this one will have no effect. In any way, this option does not override, but extends
the list of supplementary groups configured in the system group database for the user. This does not affect
commands prefixed with +.PAMName=Sets the PAM service name to set up a session as. If set, the executed process will be
registered as a PAM session under the specified service name. This is only useful in conjunction with the
User= setting, and is otherwise ignored. If not set, no PAM session will be opened for the
executed processes. See pam8 for
details.Note that for each unit making use of this option a PAM session handler process will be maintained as
part of the unit and stays around as long as the unit is active, to ensure that appropriate actions can be
taken when the unit and hence the PAM session terminates. This process is named (sd-pam) and
is an immediate child process of the unit's main process.Note that when this option is used for a unit it is very likely (depending on PAM configuration) that the
main unit process will be migrated to its own session scope unit when it is activated. This process will hence
be associated with two units: the unit it was originally started from (and for which
PAMName= was configured), and the session scope unit. Any child processes of that process
will however be associated with the session scope unit only. This has implications when used in combination
with NotifyAccess=, 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=.CapabilitiesCapabilityBoundingSet=Controls which capabilities to include in the capability bounding set for the
executed process. See capabilities7
for details. Takes a whitespace-separated list of capability names,
e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
CAP_SYS_PTRACE. Capabilities listed will be included in the bounding set, all
others are removed. If the list of capabilities is prefixed with ~, all but the
listed capabilities will be included, the effect of the assignment inverted. Note that this option
also affects the respective capabilities in the effective, permitted and inheritable capability
sets. If this option is not used, the capability bounding set is not modified on process execution,
hence no limits on the capabilities of the process are enforced. This option may appear more than
once, in which case the bounding sets are merged by OR, or by
AND if the lines are prefixed with ~ (see below). If the
empty string is assigned to this option, the bounding set is reset to the empty capability set, and
all prior settings have no effect. If set to ~ (without any further argument),
the bounding set is reset to the full set of available capabilities, also undoing any previous
settings. This does not affect commands prefixed with +.Use
systemd-analyze1's
capability command to retrieve a list of capabilities defined on the local
system.Example: if a unit has the following,
CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=CAP_B CAP_C
then CAP_A, CAP_B, and
CAP_C are set. If the second line is prefixed with
~, e.g.,
CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=~CAP_B CAP_C
then, only CAP_A is set.AmbientCapabilities=Controls which capabilities to include in the ambient capability set for the executed
process. Takes a whitespace-separated list of capability names, e.g. CAP_SYS_ADMIN,
CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. This option may appear more than
once in which case the ambient capability sets are merged (see the above examples in
CapabilityBoundingSet=). If the list of capabilities is prefixed with ~,
all but the listed capabilities will be included, the effect of the assignment inverted. If the empty string is
assigned to this option, the ambient capability set is reset to the empty capability set, and all prior
settings have no effect. If set to ~ (without any further argument), the ambient capability
set is reset to the full set of available capabilities, also undoing any previous settings. Note that adding
capabilities to ambient capability set adds them to the process's inherited capability set.
Ambient capability sets are useful if you want to execute a process as a non-privileged user but still want to
give it some capabilities. Note that in this case option keep-caps is automatically added
to SecureBits= to retain the capabilities over the user
change. AmbientCapabilities= does not affect commands prefixed with
+.SecurityNoNewPrivileges=Takes a boolean argument. If true, ensures that the service process and all its
children can never gain new privileges through execve() (e.g. via setuid or
setgid bits, or filesystem capabilities). This is the simplest and most effective way to ensure that
a process and its children can never elevate privileges again. Defaults to false, but certain
settings override this and ignore the value of this setting. This is the case when
SystemCallFilter=, SystemCallArchitectures=,
RestrictAddressFamilies=, RestrictNamespaces=,
PrivateDevices=, ProtectKernelTunables=,
ProtectKernelModules=, ProtectKernelLogs=,
ProtectClock=, MemoryDenyWriteExecute=,
RestrictRealtime=, RestrictSUIDSGID=, DynamicUser=
or LockPersonality= are specified. Note that even if this setting is overridden by them,
systemctl show shows the original value of this setting.
Also see No New Privileges
Flag.SecureBits=Controls the secure bits set for the executed process. Takes a space-separated combination of
options from the following list: , ,
, , , and
. This option may appear more than once, in which case the secure bits are
ORed. If the empty string is assigned to this option, the bits are reset to 0. This does not affect commands
prefixed with +. See capabilities7 for
details.Mandatory Access ControlSELinuxContext=Set the SELinux security context of the executed process. If set, this will override the
automated domain transition. However, the policy still needs to authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by -, all errors will be ignored. This does not
affect commands prefixed with +. See setexeccon3 for
details.AppArmorProfile=Takes a profile name as argument. The process executed by the unit will switch to
this profile when started. Profiles must already be loaded in the kernel, or the unit will fail. If
prefixed by -, all errors will be ignored. This setting has no effect if AppArmor
is not enabled. This setting does not affect commands prefixed with +.SmackProcessLabel=Takes a security label as argument. The process executed by the unit
will be started under this label and SMACK will decide whether the process is allowed to run or not, based on
it. The process will continue to run under the label specified here unless the executable has its own
label, in which case the process will transition to run under that label. When not
specified, the label that systemd is running under is used. This directive is ignored if SMACK is
disabled.The value may be prefixed by -, in which case all errors will be ignored. An empty
value may be specified to unset previous assignments. This does not affect commands prefixed with
+.Process PropertiesLimitCPU=LimitFSIZE=LimitDATA=LimitSTACK=LimitCORE=LimitRSS=LimitNOFILE=LimitAS=LimitNPROC=LimitMEMLOCK=LimitLOCKS=LimitSIGPENDING=LimitMSGQUEUE=LimitNICE=LimitRTPRIO=LimitRTTIME=Set soft and hard limits on various resources for executed processes. See
setrlimit2 for
details on the resource limit concept. Resource limits may be specified in two formats: either as
single value to set a specific soft and hard limit to the same value, or as colon-separated pair
to set both limits individually (e.g. LimitAS=4G:16G).
Use the string to configure no limit on a specific resource. The
multiplicative suffixes K, M, G, T, P and E (to the base 1024) may be used for resource limits
measured in bytes (e.g. LimitAS=16G). For the limits referring to time values, the
usual time units ms, s, min, h and so on may be used (see
systemd.time7 for
details). Note that if no time unit is specified for LimitCPU= the default unit of
seconds is implied, while for LimitRTTIME= the default unit of microseconds is
implied. Also, note that the effective granularity of the limits might influence their
enforcement. For example, time limits specified for LimitCPU= will be rounded up
implicitly to multiples of 1s. For LimitNICE= the value may be specified in two
syntaxes: if prefixed with + or -, the value is understood as
regular Linux nice value in the range -20..19. If not prefixed like this the value is understood as
raw resource limit parameter in the range 0..40 (with 0 being equivalent to 1).Note that most process resource limits configured with these options are per-process, and
processes may fork in order to acquire a new set of resources that are accounted independently of the
original process, and may thus escape limits set. Also note that LimitRSS= is not
implemented on Linux, and setting it has no effect. Often it is advisable to prefer the resource
controls listed in
systemd.resource-control5
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=.Resource limits not configured explicitly for a unit default to the value configured in the various
DefaultLimitCPU=, DefaultLimitFSIZE=, … options available in
systemd-system.conf5, and –
if not configured there – the kernel or per-user defaults, as defined by the OS (the latter only for user
services, see below).For system units these resource limits may be chosen freely. When these settings are configured
in a user service (i.e. a service run by the per-user instance of the service manager) they cannot be
used to raise the limits above those set for the user manager itself when it was first invoked, as
the user's service manager generally lacks the privileges to do so. In user context these
configuration options are hence only useful to lower the limits passed in or to raise the soft limit
to the maximum of the hard limit as configured for the user. To raise the user's limits further, the
available configuration mechanisms differ between operating systems, but typically require
privileges. In most cases it is possible to configure higher per-user resource limits via PAM or by
setting limits on the system service encapsulating the user's service manager, i.e. the user's
instance of user@.service. After making such changes, make sure to restart the
user's service manager.
Resource limit directives, their equivalent ulimit shell commands and the unit usedDirectiveulimit equivalentUnitLimitCPU=ulimit -tSecondsLimitFSIZE=ulimit -fBytesLimitDATA=ulimit -dBytesLimitSTACK=ulimit -sBytesLimitCORE=ulimit -cBytesLimitRSS=ulimit -mBytesLimitNOFILE=ulimit -nNumber of File DescriptorsLimitAS=ulimit -vBytesLimitNPROC=ulimit -uNumber of ProcessesLimitMEMLOCK=ulimit -lBytesLimitLOCKS=ulimit -xNumber of LocksLimitSIGPENDING=ulimit -iNumber of Queued SignalsLimitMSGQUEUE=ulimit -qBytesLimitNICE=ulimit -eNice LevelLimitRTPRIO=ulimit -rRealtime PriorityLimitRTTIME=No equivalentMicroseconds
UMask=Controls the file mode creation mask. Takes an access mode in octal notation. See
umask2 for
details. Defaults to 0022 for system units. For user units the default value is inherited from the
per-user service manager (whose default is in turn inherited from the system service manager, and
thus typically also is 0022 — unless overridden by a PAM module). In order to change the per-user mask
for all user services, consider setting the UMask= setting of the user's
user@.service system service instance. The per-user umask may also be set via
the umask field of a user's JSON User
Record (for users managed by
systemd-homed.service8
this field may be controlled via homectl --umask=). It may also be set via a PAM
module, such as pam_umask8.CoredumpFilter=Controls which types of memory mappings will be saved if the process dumps core
(using the /proc/pid/coredump_filter file). Takes a
whitespace-separated combination of mapping type names or numbers (with the default base 16). Mapping
type names are private-anonymous, shared-anonymous,
private-file-backed, shared-file-backed,
elf-headers, private-huge,
shared-huge, private-dax, shared-dax,
and the special values all (all types) and default (the
kernel default of private-anonymousshared-anonymouself-headersprivate-huge). See
core5
for the meaning of the mapping types. When specified multiple times, all specified masks are
ORed. When not set, or if the empty value is assigned, the inherited value is not changed.Add DAX pages to the dump filterCoredumpFilter=default private-dax shared-daxKeyringMode=Controls how the kernel session keyring is set up for the service (see session-keyring7 for
details on the session keyring). Takes one of , ,
. If set to no special keyring setup is done, and the kernel's
default behaviour is applied. If is used a new session keyring is allocated when a
service process is invoked, and it is not linked up with any user keyring. This is the recommended setting for
system services, as this ensures that multiple services running under the same system user ID (in particular
the root user) do not share their key material among each other. If is used a new
session keyring is allocated as for , but the user keyring of the user configured with
User= is linked into it, so that keys assigned to the user may be requested by the unit's
processes. In this modes multiple units running processes under the same user ID may share key material. Unless
is selected the unique invocation ID for the unit (see below) is added as a protected
key by the name invocation_id to the newly created session keyring. Defaults to
for services of the system service manager and to for
non-service units and for services of the user service manager.OOMScoreAdjust=Sets the adjustment value for the Linux kernel's Out-Of-Memory (OOM) killer score for
executed processes. Takes an integer between -1000 (to disable OOM killing of processes of this unit)
and 1000 (to make killing of processes of this unit under memory pressure very likely). See proc.txt for details. If
not specified defaults to the OOM score adjustment level of the service manager itself, which is
normally at 0.Use the OOMPolicy= setting of service units to configure how the service
manager shall react to the kernel OOM killer terminating a process of the service. See
systemd.service5
for details.TimerSlackNSec=Sets the timer slack in nanoseconds for the executed processes. The timer slack controls the
accuracy of wake-ups triggered by timers. See
prctl2 for more
information. Note that in contrast to most other time span definitions this parameter takes an integer value in
nano-seconds if no unit is specified. The usual time units are understood too.Personality=Controls which kernel architecture uname2 shall report,
when invoked by unit processes. Takes one of the architecture identifiers x86,
x86-64, ppc, ppc-le, ppc64,
ppc64-le, s390 or s390x. Which personality
architectures are supported depends on the system architecture. Usually the 64bit versions of the various
system architectures support their immediate 32bit personality architecture counterpart, but no others. For
example, x86-64 systems support the x86-64 and
x86 personalities but no others. The personality feature is useful when running 32-bit
services on a 64-bit host system. If not specified, the personality is left unmodified and thus reflects the
personality of the host system's kernel.IgnoreSIGPIPE=Takes a boolean argument. If true, causes SIGPIPE to be ignored in the
executed process. Defaults to true because SIGPIPE generally is useful only in shell
pipelines.SchedulingNice=Sets the default nice level (scheduling priority) for executed processes. Takes an integer
between -20 (highest priority) and 19 (lowest priority). See
setpriority2 for
details.CPUSchedulingPolicy=Sets the CPU scheduling policy for executed processes. Takes one of ,
, , or . See
sched_setscheduler2 for
details.CPUSchedulingPriority=Sets the CPU scheduling priority for executed processes. The available priority range depends
on the selected CPU scheduling policy (see above). For real-time scheduling policies an integer between 1
(lowest priority) and 99 (highest priority) can be used. See
sched_setscheduler2 for
details. CPUSchedulingResetOnFork=Takes a boolean argument. If true, elevated CPU scheduling priorities and policies
will be reset when the executed processes call
fork2,
and can hence not leak into child processes. See
sched_setscheduler2
for details. Defaults to false.CPUAffinity=Controls the CPU affinity of the executed processes. Takes a list of CPU indices or ranges
separated by either whitespace or commas. Alternatively, takes a special "numa" value in which case systemd
automatically derives allowed CPU range based on the value of NUMAMask= option. CPU ranges
are specified by the lower and upper CPU indices separated by a dash. This option may be specified more than
once, in which case the specified CPU affinity masks are merged. If the empty string is assigned, the mask
is reset, all assignments prior to this will have no effect. See
sched_setaffinity2 for
details.NUMAPolicy=Controls the NUMA memory policy of the executed processes. Takes a policy type, one of:
, , , and
. A list of NUMA nodes that should be associated with the policy must be specified
in NUMAMask=. For more details on each policy please see,
set_mempolicy2. For overall
overview of NUMA support in Linux see,
numa7.
NUMAMask=Controls the NUMA node list which will be applied alongside with selected NUMA policy.
Takes a list of NUMA nodes and has the same syntax as a list of CPUs for CPUAffinity=
option or special "all" value which will include all available NUMA nodes in the mask. Note that the list
of NUMA nodes is not required for and
policies and for policy we expect a single NUMA node.IOSchedulingClass=Sets the I/O scheduling class for executed processes. Takes an integer between 0 and 3 or one
of the strings , , or
. If the empty string is assigned to this option, all prior assignments to both
IOSchedulingClass= and IOSchedulingPriority= have no effect. See
ioprio_set2 for
details.IOSchedulingPriority=Sets the I/O scheduling priority for executed processes. Takes an integer between 0 (highest
priority) and 7 (lowest priority). The available priorities depend on the selected I/O scheduling class (see
above). If the empty string is assigned to this option, all prior assignments to both
IOSchedulingClass= and IOSchedulingPriority= have no effect.
See ioprio_set2 for
details.SandboxingThe 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. Similar,
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=.ProtectSystem=Takes a boolean argument or the special values full or
strict. If true, mounts the /usr/ and the boot loader
directories (/boot and /efi) read-only for processes
invoked by this unit. If set to full, the /etc/ directory is
mounted read-only, too. If set to strict the entire file system hierarchy is
mounted read-only, except for the API file system subtrees /dev/,
/proc/ and /sys/ (protect these directories using
PrivateDevices=, ProtectKernelTunables=,
ProtectControlGroups=). This setting ensures that any modification of the vendor-supplied
operating system (and optionally its configuration, and local mounts) is prohibited for the service. It is
recommended to enable this setting for all long-running services, unless they are involved with system updates
or need to modify the operating system in other ways. If this option is used,
ReadWritePaths= may be used to exclude specific directories from being made read-only. This
setting is implied if DynamicUser= is set. This setting cannot ensure protection in all
cases. In general it has the same limitations as ReadOnlyPaths=, see below. Defaults to
off.ProtectHome=Takes a boolean argument or the special values read-only or
tmpfs. If true, the directories /home/,
/root, and /run/user are made inaccessible and empty for
processes invoked by this unit. If set to read-only, the three directories are
made read-only instead. If set to tmpfs, temporary file systems are mounted on the
three directories in read-only mode. The value tmpfs is useful to hide home
directories not relevant to the processes invoked by the unit, while still allowing necessary
directories to be made visible when listed in BindPaths= or
BindReadOnlyPaths=.Setting this to yes is mostly equivalent to set 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.RuntimeDirectory=StateDirectory=CacheDirectory=LogsDirectory=ConfigurationDirectory=These options take a whitespace-separated list of directory names. The specified
directory names must be relative, and may not include ... If set, when the unit is
started, one or more directories by the specified names will be created (including their parents)
below the locations defined in the following table. Also, the corresponding environment variable will
be defined with the full paths of the directories. If multiple directories are set, then in the
environment variable the paths are concatenated with colon (:).
Automatic directory creation and environment variablesDirectoryBelow path for system unitsBelow path for user unitsEnvironment variable setRuntimeDirectory=/run/$XDG_RUNTIME_DIR$RUNTIME_DIRECTORYStateDirectory=/var/lib/$XDG_CONFIG_HOME$STATE_DIRECTORYCacheDirectory=/var/cache/$XDG_CACHE_HOME$CACHE_DIRECTORYLogsDirectory=/var/log/$XDG_CONFIG_HOME/log/$LOGS_DIRECTORYConfigurationDirectory=/etc/$XDG_CONFIG_HOME$CONFIGURATION_DIRECTORY
In case of RuntimeDirectory= the innermost subdirectories are removed when
the unit is stopped. It is possible to preserve the specified directories in this case if
RuntimeDirectoryPreserve= is configured to or
(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 in conjunction with
StateDirectory=, the logic for CacheDirectory= and
LogsDirectory= is slightly altered: the directories are created below
/var/lib/private, /var/cache/private and
/var/log/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/lib, /var/cache and
/var/log.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.d5.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.d5 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
systemctl1 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.RuntimeDirectoryMode=StateDirectoryMode=CacheDirectoryMode=LogsDirectoryMode=ConfigurationDirectoryMode=Specifies the access mode of the directories specified in RuntimeDirectory=,
StateDirectory=, CacheDirectory=, LogsDirectory=, or
ConfigurationDirectory=, respectively, as an octal number. Defaults to
0755. See "Permissions" in path_resolution7 for a
discussion of the meaning of permission bits.RuntimeDirectoryPreserve=Takes a boolean argument or . If set to (the
default), the directories specified in RuntimeDirectory= are always removed when the service
stops. If set to the directories are preserved when the service is both automatically
and manually restarted. Here, the automatic restart means the operation specified in
Restart=, and manual restart means the one triggered by systemctl restart
foo.service. If set to , then the directories are not removed when the service is
stopped. Note that since the runtime directory /run/ is a mount point of
tmpfs, then for system services the directories specified in
RuntimeDirectory= are removed when the system is rebooted.TimeoutCleanSec=Configures a timeout on the clean-up operation requested through systemctl
clean …, see
systemctl1 for
details. Takes the usual time values and defaults to infinity, i.e. by default
no timeout is applied. If a timeout is configured the clean operation will be aborted forcibly when
the timeout is reached, potentially leaving resources on disk.ReadWritePaths=ReadOnlyPaths=InaccessiblePaths=Sets up a new file system namespace for executed processes. These options may be used
to limit access a process has to the file system. Each setting takes a space-separated list of paths
relative to the host's root directory (i.e. the system running the service manager). Note that if
paths contain symlinks, they are resolved relative to the root directory set with
RootDirectory=/RootImage=.Paths listed in ReadWritePaths= are accessible from within the namespace
with the same access modes as from outside of it. Paths listed in ReadOnlyPaths=
are accessible for reading only, writing will be refused even if the usual file access controls would
permit this. Nest ReadWritePaths= inside of ReadOnlyPaths= in
order to provide writable subdirectories within read-only directories. Use
ReadWritePaths= in order to allow-list specific paths for write access if
ProtectSystem=strict is used.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=.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= and
InaccessiblePaths= 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.TemporaryFileSystem=Takes a space-separated list of mount points for temporary file systems (tmpfs). If set, a new file
system namespace is set up for executed processes, and a temporary file system is mounted on each mount point.
This option may be specified more than once, in which case temporary file systems are mounted on all listed mount
points. If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
Each mount point may optionally be suffixed with a colon (:) and mount options such as
size=10% or ro. By default, each temporary file system is mounted
with nodev,strictatime,mode=0755. These can be disabled by explicitly specifying the corresponding
mount options, e.g., dev or nostrictatime.This is useful to hide files or directories not relevant to the processes invoked by the unit, while necessary
files or directories can be still accessed by combining with BindPaths= or
BindReadOnlyPaths=:Example: if a unit has the following,
TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd
then the invoked processes by the unit cannot see any files or directories under /var/ except for
/var/lib/systemd or its contents.PrivateTmp=Takes a boolean argument. If true, sets up a new file system namespace for the
executed processes and mounts private /tmp/ and /var/tmp/
directories inside it that are not shared by processes outside of the namespace. This is useful to
secure access to temporary files of the process, but makes sharing between processes via
/tmp/ or /var/tmp/ impossible. If this is enabled, all
temporary files created by a service in these directories will be removed after the service is
stopped. Defaults to false. It is possible to run two or more units within the same private
/tmp/ and /var/tmp/ namespace by using the
JoinsNamespaceOf= directive, see
systemd.unit5 for
details. This setting is implied if DynamicUser= is set. For this setting the same
restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Enabling this setting has the side
effect of adding Requires= and After= dependencies on all mount
units necessary to access /tmp/ and /var/tmp/. Moreover an
implicitly After= ordering on
systemd-tmpfiles-setup.service8
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.PrivateDevices=Takes a boolean argument. If true, sets up a new /dev/ mount for the
executed processes and only adds API pseudo devices such as /dev/null,
/dev/zero or /dev/random (as well as the pseudo TTY subsystem) to it,
but no physical devices such as /dev/sda, system memory /dev/mem,
system ports /dev/port and others. This is useful to securely turn off physical device
access by the executed process. Defaults to false. Enabling this option will install a system call filter to
block low-level I/O system calls that are grouped in the @raw-io set, will also remove
CAP_MKNOD and CAP_SYS_RAWIO from the capability bounding set for the
unit (see above), and set DevicePolicy=closed (see
systemd.resource-control5
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
mmap2 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. If turned on and if running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.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.PrivateNetwork=Takes a boolean argument. If true, sets up a new network namespace for the executed processes
and configures only the loopback network device lo inside it. No other network devices will
be available to the executed process. This is useful to turn off network access by the executed process.
Defaults to false. It is possible to run two or more units within the same private network namespace by using
the JoinsNamespaceOf= directive, see
systemd.unit5 for
details. Note that this option will disconnect all socket families from the host, including
AF_NETLINK and AF_UNIX. Effectively, for
AF_NETLINK this means that device configuration events received from
systemd-udevd.service8 are
not delivered to the unit's processes. And for AF_UNIX this has the effect that
AF_UNIX sockets in the abstract socket namespace of the host will become unavailable to
the unit's processes (however, those located in the file system will continue to be accessible).Note that the implementation of this setting might be impossible (for example if network namespaces are
not available), and the unit should be written in a way that does not solely rely on this setting for
security.When this option is 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.NetworkNamespacePath=Takes an absolute file system path refererring to a Linux network namespace
pseudo-file (i.e. a file like /proc/$PID/ns/net or a bind mount or symlink to
one). When set the invoked processes are added to the network namespace referenced by that path. The
path has to point to a valid namespace file at the moment the processes are forked off. If this
option is used PrivateNetwork= has no effect. If this option is used together with
JoinsNamespaceOf= then it only has an effect if this unit is started before any of
the listed units that have PrivateNetwork= or
NetworkNamespacePath= configured, as otherwise the network namespace of those
units is reused.When this option is used on a socket unit any sockets bound on behalf of this unit will be
bound within the specified network namespace.PrivateUsers=Takes a boolean argument. If true, sets up a new user namespace for the executed processes and
configures a minimal user and group mapping, that maps the root user and group as well as
the unit's own user and group to themselves and everything else to the nobody user and
group. This is useful to securely detach the user and group databases used by the unit from the rest of the
system, and thus to create an effective sandbox environment. All files, directories, processes, IPC objects and
other resources owned by users/groups not equaling root or the unit's own will stay visible
from within the unit but appear owned by the nobody user and group. If this mode is enabled,
all unit processes are run without privileges in the host user namespace (regardless if the unit's own
user/group is root or not). Specifically this means that the process will have zero process
capabilities on the host's user namespace, but full capabilities within the service's user namespace. Settings
such as CapabilityBoundingSet= will affect only the latter, and there's no way to acquire
additional capabilities in the host's user namespace. Defaults to off.When this setting is set up by a per-user instance of the service manager, the mapping of the
root user and group to itself is omitted (unless the user manager is root).
Additionally, in the per-user instance manager case, the
user namespace will be set up before most other namespaces. This means that combining
PrivateUsers= 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.ProtectHostname=Takes a boolean argument. When set, sets up a new UTS namespace for the executed
processes. In addition, changing hostname or domainname is prevented. Defaults to off.Note that the implementation of this setting might be impossible (for example if UTS namespaces
are not available), and the unit should be written in a way that does not solely rely on this setting
for security.Note that when this option is enabled for a service hostname changes no longer propagate from
the system into the service, it is hence not suitable for services that need to take notice of system
hostname changes dynamically.ProtectClock=Takes a boolean argument. If set, writes to the hardware clock or system clock will be denied.
It is recommended to turn this on for most services that do not need modify the clock. Defaults to off. Enabling
this option removes CAP_SYS_TIME and CAP_WAKE_ALARM from the
capability bounding set for this unit, installs a system call filter to block calls that can set the
clock, and DeviceAllow=char-rtc r is implied. This ensures /dev/rtc0,
/dev/rtc1, etc. are made read-only to the service. See
systemd.resource-control5
for the details about DeviceAllow=.ProtectKernelTunables=Takes a boolean argument. If true, kernel variables accessible through
/proc/sys/, /sys/, /proc/sysrq-trigger,
/proc/latency_stats, /proc/acpi,
/proc/timer_stats, /proc/fs and /proc/irq will
be made read-only to all processes of the unit. Usually, tunable kernel variables should be initialized only at
boot-time, for example with the
sysctl.d5 mechanism. Few
services need to write to these at runtime; it is hence recommended to turn this on for most services. For this
setting the same restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Defaults to off. If turned on and if running
in user mode, or in system mode, but without the CAP_SYS_ADMIN capability (e.g. services
for which User= is set), NoNewPrivileges=yes is implied. Note that this
option does not prevent indirect changes to kernel tunables effected by IPC calls to other processes. However,
InaccessiblePaths= may be used to make relevant IPC file system objects inaccessible. If
ProtectKernelTunables= is set, MountAPIVFS=yes is
implied.ProtectKernelModules=Takes a boolean argument. If true, explicit module loading will be denied. This allows
module load and unload operations to be turned off on modular kernels. It is recommended to turn this on for most services
that do not need special file systems or extra kernel modules to work. Defaults to off. Enabling this option
removes CAP_SYS_MODULE from the capability bounding set for the unit, and installs a
system call filter to block module system calls, also /usr/lib/modules is made
inaccessible. For this setting the same restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Note that limited automatic module loading due
to user configuration or kernel mapping tables might still happen as side effect of requested user operations,
both privileged and unprivileged. To disable module auto-load feature please see
sysctl.d5kernel.modules_disabled mechanism and
/proc/sys/kernel/modules_disabled documentation. If turned on and if running in user
mode, or in system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied.ProtectKernelLogs=Takes a boolean argument. If true, access to the kernel log ring buffer will be denied. It is
recommended to turn this on for most services that do not need to read from or write to the kernel log ring
buffer. Enabling this option removes CAP_SYSLOG from the capability bounding set for this
unit, and installs a system call filter to block the
syslog2
system call (not to be confused with the libc API
syslog3
for userspace logging). The kernel exposes its log buffer to userspace via /dev/kmsg and
/proc/kmsg. If enabled, these are made inaccessible to all the processes in the unit.ProtectControlGroups=Takes a boolean argument. If true, the Linux Control Groups (cgroups7) hierarchies
accessible through /sys/fs/cgroup/ will be made read-only to all processes of the
unit. Except for container managers no services should require write access to the control groups hierarchies;
it is hence recommended to turn this on for most services. For this setting the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths= and related calls, see
above. Defaults to off. If ProtectControlGroups= is set, MountAPIVFS=yes
is implied.RestrictAddressFamilies=Restricts the set of socket address families accessible to the processes of this
unit. Takes a space-separated list of address family names to allow-list, such as
AF_UNIX, AF_INET or AF_INET6. When
prefixed with ~ the listed address families will be applied as deny list,
otherwise as allow list. Note that this restricts access to the socket2
system call only. Sockets passed into the process by other means (for example, by using socket
activation with socket units, see
systemd.socket5)
are unaffected. Also, sockets created with socketpair() (which creates connected
AF_UNIX sockets only) are unaffected. Note that this option has no effect on 32-bit x86, s390, s390x,
mips, mips-le, ppc, ppc-le, ppc64, ppc64-le and is ignored (but works correctly on other ABIs,
including x86-64). Note that on systems supporting multiple ABIs (such as x86/x86-64) it is
recommended to turn off alternative ABIs for services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user mode, or in system
mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=nobody), NoNewPrivileges=yes is implied. 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
syslog2
logging.RestrictNamespaces=Restricts access to Linux namespace functionality for the processes of this unit. For details
about Linux namespaces, see namespaces7. Either
takes a boolean argument, or a space-separated list of namespace type identifiers. If false (the default), no
restrictions on namespace creation and switching are made. If true, access to any kind of namespacing is
prohibited. Otherwise, a space-separated list of namespace type identifiers must be specified, consisting of
any combination of: cgroup, ipc, net,
mnt, pid, user and uts. Any
namespace type listed is made accessible to the unit's processes, access to namespace types not listed is
prohibited (allow-listing). By prepending the list with a single tilde character (~) the
effect may be inverted: only the listed namespace types will be made inaccessible, all unlisted ones are
permitted (deny-listing). If the empty string is assigned, the default namespace restrictions are applied,
which is equivalent to false. This option may appear more than once, in which case the namespace types are
merged by OR, or by AND if the lines are prefixed with
~ (see examples below). Internally, this setting limits access to the
unshare2,
clone2 and
setns2 system calls, taking
the specified flags parameters into account. Note that — if this option is used — in addition to restricting
creation and switching of the specified types of namespaces (or all of them, if true) access to the
setns() system call with a zero flags parameter is prohibited. This setting is only
supported on x86, x86-64, mips, mips-le, mips64, mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390
and s390x, and enforces no restrictions on other architectures. If running in user mode, or in system mode, but
without the CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.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.LockPersonality=Takes a boolean argument. If set, locks down the personality2 system
call so that the kernel execution domain may not be changed from the default or the personality selected with
Personality= directive. This may be useful to improve security, because odd personality
emulations may be poorly tested and source of vulnerabilities. If running in user mode, or in system mode, but
without the CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.MemoryDenyWriteExecute=Takes a boolean argument. If set, attempts to create memory mappings that are writable and
executable at the same time, or to change existing memory mappings to become executable, or mapping shared
memory segments as executable are prohibited. Specifically, a system call filter is added that rejects
mmap2 system calls with both
PROT_EXEC and PROT_WRITE set,
mprotect2 or
pkey_mprotect2 system calls
with PROT_EXEC set and
shmat2 system calls with
SHM_EXEC set. Note that this option is incompatible with programs and libraries that
generate program code dynamically at runtime, including JIT execution engines, executable stacks, and code
"trampoline" feature of various C compilers. This option improves service security, as it makes harder for
software exploits to change running code dynamically. However, the protection can be circumvented, if
the service can write to a filesystem, which is not mounted with noexec (such as
/dev/shm), or it can use memfd_create(). This can be
prevented by making such file systems inaccessible to the service
(e.g. InaccessiblePaths=/dev/shm) and installing further system call filters
(SystemCallFilter=~memfd_create). Note that this feature is fully available on
x86-64, and partially on x86. Specifically, the shmat() protection is not
available on x86. Note that on systems supporting multiple ABIs (such as x86/x86-64) it is
recommended to turn off alternative ABIs for services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user mode, or in system
mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied.RestrictRealtime=Takes a boolean argument. If set, any attempts to enable realtime scheduling in a process of
the unit are refused. This restricts access to realtime task scheduling policies such as
SCHED_FIFO, SCHED_RR or SCHED_DEADLINE. See
sched7
for details about these scheduling policies. If running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied. Realtime scheduling policies may be used to monopolize CPU
time for longer periods of time, and may hence be used to lock up or otherwise trigger Denial-of-Service
situations on the system. It is hence recommended to restrict access to realtime scheduling to the few programs
that actually require them. Defaults to off.RestrictSUIDSGID=Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
set-group-ID (SGID) bits on files or directories will be denied (for details on these bits see
inode7). If
running in user mode, or in system mode, but without the CAP_SYS_ADMIN
capability (e.g. setting User=), NoNewPrivileges=yes is
implied. As the SUID/SGID bits are mechanisms to elevate privileges, and allows users to acquire the
identity of other users, it is recommended to restrict creation of SUID/SGID files to the few
programs that actually require them. Note that this restricts marking of any type of file system
object with these bits, including both regular files and directories (where the SGID is a different
meaning than for files, see documentation). This option is implied if DynamicUser=
is enabled. Defaults to off.RemoveIPC=Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user and
group the processes of this unit are run as are removed when the unit is stopped. This setting only has an
effect if at least one of User=, Group= and
DynamicUser= are used. It has no effect on IPC objects owned by the root user. Specifically,
this removes System V semaphores, as well as System V and POSIX shared memory segments and message queues. If
multiple units use the same user or group the IPC objects are removed when the last of these units is
stopped. This setting is implied if DynamicUser= is set.PrivateMounts=Takes a boolean parameter. If set, the processes of this unit will be run in their own private
file system (mount) namespace with all mount propagation from the processes towards the host's main file system
namespace turned off. This means any file system mount points established or removed by the unit's processes
will be private to them and not be visible to the host. However, file system mount points established or
removed on the host will be propagated to the unit's processes. See mount_namespaces7 for
details on file system namespaces. Defaults to off.When turned on, this executes three operations for each invoked process: a new
CLONE_NEWNS namespace is created, after which all existing mounts are remounted to
MS_SLAVE to disable propagation from the unit's processes to the host (but leaving
propagation in the opposite direction in effect). Finally, the mounts are remounted again to the propagation
mode configured with MountFlags=, see below.File system namespaces are set up individually for each process forked off by the service manager. Mounts
established in the namespace of the process created by ExecStartPre= will hence be cleaned
up automatically as soon as that process exits and will not be available to subsequent processes forked off for
ExecStart= (and similar applies to the various other commands configured for
units). Similarly, JoinsNamespaceOf= does not permit sharing kernel mount namespaces between
units, it only enables sharing of the /tmp/ and /var/tmp/
directories.Other file system namespace unit settings — PrivateMounts=,
PrivateTmp=, PrivateDevices=, ProtectSystem=,
ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=,
ReadWritePaths=, … — also enable file system namespacing in a fashion equivalent to this
option. Hence it is primarily useful to explicitly request this behaviour if none of the other settings are
used.MountFlags=Takes a mount propagation setting: , or
, which controls whether file system mount points in the file system namespaces set up
for this unit's processes will receive or propagate mounts and unmounts from other file system namespaces. See
mount2
for details on mount propagation, and the three propagation flags in particular.This setting only controls the final propagation setting in effect on all mount
points of the file system namespace created for each process of this unit. Other file system namespacing unit
settings (see the discussion in PrivateMounts= above) will implicitly disable mount and
unmount propagation from the unit's processes towards the host by changing the propagation setting of all mount
points in the unit's file system namespace to first. Setting this option to
does not reestablish propagation in that case.If not set – but file system namespaces are enabled through another file system namespace unit setting –
mount propagation is used, but — as mentioned — as is applied
first, propagation from the unit's processes to the host is still turned off.It is not recommended to use mount propagation for units, as this means
temporary mounts (such as removable media) of the host will stay mounted and thus indefinitely busy in forked
off processes, as unmount propagation events won't be received by the file system namespace of the unit.Usually, it is best to leave this setting unmodified, and use higher level file system namespacing
options instead, in particular PrivateMounts=, see above.System Call FilteringSystemCallFilter=Takes a space-separated list of system call names. If this setting is used, all
system calls executed by the unit processes except for the listed ones will result in immediate
process termination with the SIGSYS signal (allow-listing). (See
SystemCallErrorNumber= below for changing the default action). If the first
character of the list is ~, the effect is inverted: only the listed system calls
will result in immediate process termination (deny-listing). Deny-listed system calls and system call
groups may optionally be suffixed with a colon (:) and errno
error number (between 0 and 4095) or errno name such as EPERM,
EACCES or EUCLEAN (see errno3 for a
full list). This value will be returned when a deny-listed system call is triggered, instead of
terminating the processes immediately. Special setting kill can be used to
explicitly specify killing. This value takes precedence over the one given in
SystemCallErrorNumber=, see below. If running in user mode, or in system mode,
but without the CAP_SYS_ADMIN capability (e.g. setting
User=nobody), NoNewPrivileges=yes is implied. This feature
makes use of the Secure Computing Mode 2 interfaces of the kernel ('seccomp filtering') and is useful
for enforcing a minimal sandboxing environment. Note that the execve(),
exit(), exit_group(), getrlimit(),
rt_sigreturn(), sigreturn() system calls and the system calls
for querying time and sleeping are implicitly allow-listed and do not need to be listed
explicitly. This option may be specified more than once, in which case the filter masks are
merged. If the empty string is assigned, the filter is reset, all prior assignments will have no
effect. This does not affect commands prefixed with +.Note that on systems supporting multiple ABIs (such as x86/x86-64) it is recommended to turn off
alternative ABIs for services, so that they cannot be used to circumvent the restrictions of this
option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar.Note that strict system call filters may impact execution and error handling code paths of the service
invocation. Specifically, access to the execve() system call is required for the execution
of the service binary — if it is blocked service invocation will necessarily fail. Also, if execution of the
service binary fails for some reason (for example: missing service executable), the error handling logic might
require access to an additional set of system calls in order to process and log this failure correctly. It
might be necessary to temporarily disable system call filters in order to simplify debugging of such
failures.If you specify both types of this option (i.e. allow-listing and deny-listing), the first
encountered will take precedence and will dictate the default action (termination or approval of a
system call). Then the next occurrences of this option will add or delete the listed system calls
from the set of the filtered system calls, depending of its type and the default action. (For
example, if you have started with an allow list rule for read() and
write(), and right after it add a deny list rule for write(),
then write() will be removed from the set.)As the number of possible system calls is large, predefined sets of system calls are provided. A set
starts with @ character, followed by name of the set.
Currently predefined system call setsSetDescription@aioAsynchronous I/O (io_setup2, io_submit2, and related calls)@basic-ioSystem calls for basic I/O: reading, writing, seeking, file descriptor duplication and closing (read2, write2, and related calls)@chownChanging file ownership (chown2, fchownat2, and related calls)@clockSystem calls for changing the system clock (adjtimex2, settimeofday2, and related calls)@cpu-emulationSystem calls for CPU emulation functionality (vm862 and related calls)@debugDebugging, performance monitoring and tracing functionality (ptrace2, perf_event_open2 and related calls)@file-systemFile system operations: opening, creating files and directories for read and write, renaming and removing them, reading file properties, or creating hard and symbolic links@io-eventEvent loop system calls (poll2, select2, epoll7, eventfd2 and related calls)@ipcPipes, SysV IPC, POSIX Message Queues and other IPC (mq_overview7, svipc7)@keyringKernel keyring access (keyctl2 and related calls)@memlockLocking of memory in RAM (mlock2, mlockall2 and related calls)@moduleLoading and unloading of kernel modules (init_module2, delete_module2 and related calls)@mountMounting and unmounting of file systems (mount2, chroot2, and related calls)@network-ioSocket I/O (including local AF_UNIX): socket7, unix7@obsoleteUnusual, obsolete or unimplemented (create_module2, gtty2, …)@privilegedAll system calls which need super-user capabilities (capabilities7)@processProcess control, execution, namespacing operations (clone2, kill2, namespaces7, …)@raw-ioRaw I/O port access (ioperm2, iopl2, pciconfig_read(), …)@rebootSystem calls for rebooting and reboot preparation (reboot2, kexec(), …)@resourcesSystem calls for changing resource limits, memory and scheduling parameters (setrlimit2, setpriority2, …)@setuidSystem calls for changing user ID and group ID credentials, (setuid2, setgid2, setresuid2, …)@signalSystem calls for manipulating and handling process signals (signal2, sigprocmask2, …)@swapSystem calls for enabling/disabling swap devices (swapon2, swapoff2)@syncSynchronizing files and memory to disk (fsync2, msync2, and related calls)@system-serviceA reasonable set of system calls used by common system services, excluding any special purpose calls. This is the recommended starting point for allow-listing system calls for system services, as it contains what is typically needed by system services, but excludes overly specific interfaces. For example, the following APIs are excluded: @clock, @mount, @swap, @reboot.@timerSystem calls for scheduling operations by time (alarm2, timer_create2, …)@knownAll system calls defined by the kernel. This list is defined statically in systemd based on a kernel version that was available when this systemd version was released. It will become progressively more out-of-date as the kernel is updated.
Note, that as new system calls are added to the kernel, additional system calls might be added to the groups
above. Contents of the sets may also change between systemd versions. In addition, the list of system calls
depends on the kernel version and architecture for which systemd was compiled. Use
systemd-analyze syscall-filter to list the actual list of system calls in each
filter.Generally, allow-listing system calls (rather than deny-listing) is the safer mode of
operation. It is recommended to enforce system call allow lists for all long-running system
services. Specifically, the following lines are a relatively safe basic choice for the majority of
system services:[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERMNote 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=.SystemCallErrorNumber=Takes an errno error number (between 1 and 4095) or errno name
such as EPERM, EACCES or EUCLEAN, to
return when the system call filter configured with SystemCallFilter= is triggered,
instead of terminating the process immediately. See errno3 for a
full list of error codes. When this setting is not used, or when the empty string or the special
setting kill is assigned, the process will be terminated immediately when the
filter is triggered.SystemCallArchitectures=Takes a space-separated list of architecture identifiers to include in the system call
filter. The known architecture identifiers are the same as for ConditionArchitecture=
described in systemd.unit5,
as well as x32, mips64-n32, mips64-le-n32, and
the special identifier native. The special identifier native
implicitly maps to the native architecture of the system (or more precisely: to the architecture the system
manager is compiled for). If running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=nobody),
NoNewPrivileges=yes is implied. By default, this option is set to the empty list, i.e. no
filtering is applied.If this setting is used, processes of this unit will only be permitted to call native system calls, and
system calls of the specified architectures. For the purposes of this option, the x32 architecture is treated
as including x86-64 system calls. However, this setting still fulfills its purpose, as explained below, on
x32.System call filtering is not equally effective on all architectures. For example, on x86
filtering of network socket-related calls is not possible, due to ABI limitations — a limitation that x86-64
does not have, however. On systems supporting multiple ABIs at the same time — such as x86/x86-64 — it is hence
recommended to limit the set of permitted system call architectures so that secondary ABIs may not be used to
circumvent the restrictions applied to the native ABI of the system. In particular, setting
SystemCallArchitectures=native is a good choice for disabling non-native ABIs.System call architectures may also be restricted system-wide via the
SystemCallArchitectures= option in the global configuration. See
systemd-system.conf5 for
details.SystemCallLog=Takes a space-separated list of system call names. If this setting is used, all
system calls executed by the unit processes for the listed ones will be logged. If the first
character of the list is ~, the effect is inverted: all system calls except the
listed system calls will be logged. If running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=nobody),
NoNewPrivileges=yes is implied. This feature makes use of the Secure Computing
Mode 2 interfaces of the kernel ('seccomp filtering') and is useful for auditing or setting up a
minimal sandboxing environment. This option may be specified more than once, in which case the filter
masks are merged. If the empty string is assigned, the filter is reset, all prior assignments will
have no effect. This does not affect commands prefixed with +.EnvironmentEnvironment=Sets environment variables for executed processes. Takes a space-separated list of
variable assignments. This option may be specified more than once, in which case all listed variables
will be set. If the same variable is set twice, the later setting will override the earlier
setting. If the empty string is assigned to this option, the list of environment variables is reset,
all prior assignments have no effect. Variable expansion is not performed inside the strings,
however, specifier expansion is possible. The $ character has no special
meaning. If you need to assign a value containing spaces or the equals sign to a variable, use double
quotes (") for the assignment.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 environ7 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= (see below) to pass data to unit processes
securely.EnvironmentFile=Similar to Environment= but reads the environment variables from a text
file. The text file should contain new-line-separated variable assignments. Empty lines, lines without an
= separator, or lines starting with ; or # will be ignored, which may be used for
commenting. A line ending with a backslash will be concatenated with the following one, allowing multiline
variable definitions. The parser strips leading and trailing whitespace from the values of assignments, unless
you use double quotes (").C escapes
are supported, but not
most control characters.
\t and \n can be used to insert tabs and newlines within
EnvironmentFile=.The argument passed should be an absolute filename or wildcard expression, optionally prefixed with
-, which indicates that if the file does not exist, it will not be read and no error or
warning message is logged. This option may be specified more than once in which case all specified files are
read. If the empty string is assigned to this option, the list of file to read is reset, all prior assignments
have no effect.The files listed with this directive will be read shortly before the process is executed (more
specifically, after all processes from a previous unit state terminated. This means you can generate these
files in one unit state, and read it with this option in the next. The files are read from the file
system of the service manager, before any file system changes like bind mounts take place).Settings from these files override settings made with Environment=. If the same
variable is set twice from these files, the files will be read in the order they are specified and the later
setting will override the earlier setting.PassEnvironment=Pass environment variables set for the system service manager to executed processes. Takes a
space-separated list of variable names. This option may be specified more than once, in which case all listed
variables will be passed. If the empty string is assigned to this option, the list of environment variables to
pass is reset, all prior assignments have no effect. Variables specified that are not set for the system
manager will not be passed and will be silently ignored. Note that this option is only relevant for the system
service manager, as system services by default do not automatically inherit any environment variables set for
the service manager itself. However, in case of the user service manager all environment variables are passed
to the executed processes anyway, hence this option is without effect for the user service manager.Variables set for invoked processes due to this setting are subject to being overridden by those
configured with Environment= or EnvironmentFile=.C escapes
are supported, but not
most control characters.
\t and \n can be used to insert tabs and newlines within
EnvironmentFile=.Example:
PassEnvironment=VAR1 VAR2 VAR3
passes three variables VAR1,
VAR2, VAR3
with the values set for those variables in PID1.
See environ7 for details
about environment variables.UnsetEnvironment=Explicitly unset environment variable assignments that would normally be passed from the
service manager to invoked processes of this unit. Takes a space-separated list of variable names or variable
assignments. This option may be specified more than once, in which case all listed variables/assignments will
be unset. If the empty string is assigned to this option, the list of environment variables/assignments to
unset is reset. If a variable assignment is specified (that is: a variable name, followed by
=, followed by its value), then any environment variable matching this precise assignment is
removed. If a variable name is specified (that is a variable name without any following = or
value), then any assignment matching the variable name, regardless of its value is removed. Note that the
effect of UnsetEnvironment= is applied as final step when the environment list passed to
executed processes is compiled. That means it may undo assignments from any configuration source, including
assignments made through Environment= or EnvironmentFile=, inherited from
the system manager's global set of environment variables, inherited via PassEnvironment=,
set by the service manager itself (such as $NOTIFY_SOCKET and such), or set by a PAM module
(in case PAMName= is used).
See environ7 for details
about environment variables.Logging and Standard Input/OutputStandardInput=Controls where file descriptor 0 (STDIN) of the executed processes is connected to. Takes one
of , , , ,
, , or
.If is selected, standard input will be connected to /dev/null,
i.e. all read attempts by the process will result in immediate EOF.If is selected, standard input is connected to a TTY (as configured by
TTYPath=, see below) and the executed process becomes the controlling process of the
terminal. If the terminal is already being controlled by another process, the executed process waits until the
current controlling process releases the terminal. is similar to , but the executed process is forcefully and
immediately made the controlling process of the terminal, potentially removing previous controlling processes
from the terminal. is similar to , but if the terminal already has a
controlling process start-up of the executed process fails.The option 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 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 option is valid in socket-activated services only, and requires the relevant
socket unit file (see
systemd.socket5 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 inetd8 socket activation
daemon.The 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.socket5 for more
details about named file descriptors and their ordering.This setting defaults to .StandardOutput=Controls where file descriptor 1 (stdout) of the executed processes is connected
to. Takes one of , , ,
, , ,
, ,
, or
. duplicates the file descriptor of standard input for standard output. connects standard output to /dev/null, i.e. everything written
to it will be lost. 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. connects standard output with the journal, which is accessible via
journalctl1. 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.) connects standard output with the kernel log buffer which is accessible via
dmesg1,
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 . and work in a similar way as the
two options above but copy the output to the system console as well.The option may be used to connect a specific file
system object to standard output. The semantics are similar to the same option of
StandardInput=, see above. If path refers to a regular file
on the filesystem, it is opened (created if it doesn't exist yet) for writing at the beginning of the file,
but without truncating it.
If standard input and output are directed to the same file path, it is opened only once, for reading as well
as writing and duplicated. This is particularly useful when the specified path refers to an
AF_UNIX socket in the file system, as in that case only a
single stream connection is created for both input and output. is similar to
above, but it opens the file in append mode.
connects standard output to a socket acquired via socket activation. The
semantics are similar to the same option of StandardInput=, see above.The 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.socket5 for more
details about named descriptors and their ordering.If the standard output (or error output, see below) of a unit is connected to the journal or
the kernel log buffer, the unit will implicitly gain a dependency of type After=
on systemd-journald.socket (also see the "Implicit Dependencies" section
above). Also note that in this case stdout (or stderr, see below) will be an
AF_UNIX stream socket, and not a pipe or FIFO that can be re-opened. This means
when executing shell scripts the construct echo "hello" > /dev/stderr for
writing text to stderr will not work. To mitigate this use the construct echo "hello"
>&2 instead, which is mostly equivalent and avoids this pitfall.This setting defaults to the value set with DefaultStandardOutput= in
systemd-system.conf5, which
defaults to . Note that setting this parameter might result in additional dependencies
to be added to the unit (see above).StandardError=Controls where file descriptor 2 (stderr) of the executed processes is connected to. The
available options are identical to those of StandardOutput=, with some exceptions: if set to
the file descriptor used for standard output is duplicated for standard error, while
will use a default file descriptor name of
stderr.This setting defaults to the value set with DefaultStandardError= in
systemd-system.conf5, which
defaults to . Note that setting this parameter might result in additional dependencies
to be added to the unit (see above).StandardInputText=StandardInputData=Configures arbitrary textual or binary data to pass via file descriptor 0 (STDIN) to the
executed processes. These settings have no effect unless StandardInput= is set to
. Use this option to embed process input data directly in the unit file.StandardInputText= accepts arbitrary textual data. C-style escapes for special
characters as well as the usual %-specifiers are resolved. Each time this setting is used
the specified text is appended to the per-unit data buffer, followed by a newline character (thus every use
appends a new line to the end of the buffer). Note that leading and trailing whitespace of lines configured
with this option is removed. If an empty line is specified the buffer is cleared (hence, in order to insert an
empty line, add an additional \n to the end or beginning of a line).StandardInputData= accepts arbitrary binary data, encoded in Base64. 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.unit5 for
details). This is particularly useful for large data configured with these two options. Example:…
StandardInput=data
StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy4KSWNrIGtpZWtl \
LCBzdGF1bmUsIHd1bmRyZSBtaXIsCnVmZiBlZW1hbCBqZWh0IHNlIHVmZiBkaWUgVMO8ci4KTmFu \
dSwgZGVuayBpY2ssIGljayBkZW5rIG5hbnUhCkpldHogaXNzZSB1ZmYsIGVyc2NodCB3YXIgc2Ug \
enUhCkljayBqZWhlIHJhdXMgdW5kIGJsaWNrZSDigJQKdW5kIHdlciBzdGVodCBkcmF1w59lbj8g \
SWNrZSEK
…LogLevelMax=Configures filtering by log level of log messages generated by this unit. Takes a
syslog log level, one of (lowest log level, only highest priority
messages), , , , ,
, , (highest log level, also lowest priority
messages). See syslog3 for
details. By default no filtering is applied (i.e. the default maximum log level is ). Use
this option to configure the logging system to drop log messages of a specific service above the specified
level. For example, set LogLevelMax= in order to turn off debug logging
of a particularly chatty unit. Note that the configured level is applied to any log messages written by any
of the processes belonging to this unit, sent via any supported logging protocol. The filtering is applied
early in the logging pipeline, before any kind of further processing is done. Moreover, messages which pass
through this filter successfully might still be dropped by filters applied at a later stage in the logging
subsystem. For example, MaxLevelStore= configured in
journald.conf5 might
prohibit messages of higher log levels to be stored on disk, even though the per-unit
LogLevelMax= permitted it to be processed.LogExtraFields=Configures additional log metadata fields to include in all log records generated by
processes associated with this unit. This setting takes one or more journal field assignments in the
format FIELD=VALUE separated by whitespace. See
systemd.journal-fields7
for details on the journal field concept. Even though the underlying journal implementation permits
binary field values, this setting accepts only valid UTF-8 values. To include space characters in a
journal field value, enclose the assignment in double quotes (").
The usual specifiers are expanded in all assignments (see below). Note that this setting is not only
useful for attaching additional metadata to log records of a unit, but given that all fields and
values are indexed may also be used to implement cross-unit log record matching. Assign an empty
string to reset the list.LogRateLimitIntervalSec=LogRateLimitBurst=Configures the rate limiting that is applied to messages generated by this unit. If, in the
time interval defined by LogRateLimitIntervalSec=, more messages than specified in
LogRateLimitBurst= are logged by a service, all further messages within the interval are
dropped until the interval is over. A message about the number of dropped messages is generated. The time
specification for LogRateLimitIntervalSec= may be specified in the following units: "s",
"min", "h", "ms", "us" (see
systemd.time7 for details).
The default settings are set by RateLimitIntervalSec= and RateLimitBurst=
configured in journald.conf5.
LogNamespace=Run the unit's processes in the specified journal namespace. Expects a short
user-defined string identifying the namespace. If not used the processes of the service are run in
the default journal namespace, i.e. their log stream is collected and processed by
systemd-journald.service. If this option is used any log data generated by
processes of this unit (regardless if via the syslog(), journal native logging
or stdout/stderr logging) is collected and processed by an instance of the
systemd-journald@.service template unit, which manages the specified
namespace. The log data is stored in a data store independent from the default log namespace's data
store. See
systemd-journald.service8
for details about journal namespaces.Internally, journal namespaces are implemented through Linux mount namespacing and
over-mounting the directory that contains the relevant AF_UNIX sockets used for
logging in the unit's mount namespace. Since mount namespaces are used this setting disconnects
propagation of mounts from the unit's processes to the host, similar to how
ReadOnlyPaths= and similar settings (see above) work. Journal namespaces may hence
not be used for services that need to establish mount points on the host.When this option is used the unit will automatically gain ordering and requirement dependencies
on the two socket units associated with the systemd-journald@.service instance
so that they are automatically established prior to the unit starting up. Note that when this option
is used log output of this service does not appear in the regular
journalctl1
output, unless the option is used.SyslogIdentifier=Sets the process name ("syslog tag") to prefix log lines sent to
the logging system or the kernel log buffer with. If not set, defaults to the process name of the
executed process. This option is only useful when StandardOutput= or
StandardError= are set to or (or to
the same settings in combination with ) and only applies to log messages
written to stdout or stderr.SyslogFacility=Sets the syslog facility identifier to use when logging. One of
, , , ,
, , , ,
, , , ,
, , , ,
, , or
. See syslog3 for
details. This option is only useful when StandardOutput= or
StandardError= are set to or (or to
the same settings in combination with ), and only applies to log messages
written to stdout or stderr. Defaults to .SyslogLevel=The default syslog log level to use when logging to the logging system or
the kernel log buffer. One of , , ,
, , , ,
. See syslog3 for
details. This option is only useful when StandardOutput= or
StandardError= are set to or
(or to the same settings in combination with ), and only applies
to log messages written to stdout or stderr. Note that individual lines output by executed processes may be
prefixed with a different log level which can be used to override the default log level specified here. The
interpretation of these prefixes may be disabled with SyslogLevelPrefix=, see below. For
details, see sd-daemon3.
Defaults to .SyslogLevelPrefix=Takes a boolean argument. If true and StandardOutput= or
StandardError= are set to or (or to
the same settings in combination with ), log lines written by the executed
process that are prefixed with a log level will be processed with this log level set but the prefix
removed. If set to false, the interpretation of these prefixes is disabled and the logged lines are
passed on as-is. This only applies to log messages written to stdout or stderr. For details about
this prefixing see
sd-daemon3.
Defaults to true.TTYPath=Sets the terminal device node to use if standard input, output, or error are connected to a TTY
(see above). Defaults to /dev/console.TTYReset=Reset the terminal device specified with TTYPath= before and after
execution. Defaults to no.TTYVHangup=Disconnect all clients which have opened the terminal device specified with
TTYPath= before and after execution. Defaults to no.TTYVTDisallocate=If the terminal device specified with TTYPath= is a virtual console
terminal, try to deallocate the TTY before and after execution. This ensures that the screen and scrollback
buffer is cleared. Defaults to no.CredentialsLoadCredential=ID:PATHPass a credential to the unit. Credentials are limited-size binary or textual objects
that may be passed to unit processes. They are primarily used for passing cryptographic keys (both
public and private) or certificates, user account information or identity information from host to
services. The data is accessible from the unit's processes via the file system, at a read-only
location that (if possible and permitted) is backed by non-swappable memory. The data is only
accessible to the user associated with the unit, via the
User=/DynamicUser= settings (as well as the superuser). When
available, the location of credentials is exported as the $CREDENTIALS_DIRECTORY
environment variable to the unit's processes.The LoadCredential= setting takes a textual ID to use as name for a
credential plus a file system path. 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 providing credentials from other services. If the specified path is not
absolute and itself qualifies as valid credential identifier it is understood to refer to a
credential that the service manager itself received via the $CREDENTIALS_DIRECTORY
environment variable, which may be used to propagate credentials from an invoking environment (e.g. a
container manager that invoked the service manager) into a service. The contents of the file/socket
may be arbitrary binary or textual data, including newline characters and NUL
bytes. This option may be used multiple times, each time defining an additional credential to pass to
the unit.The credential files/IPC sockets must be accessible to the service manager, but don't have to
be directly accessible to the unit's processes: the credential data is read and copied into separate,
read-only copies for the unit that are accessible to appropriately privileged processes. This is
particularly useful in combination with DynamicUser= as this way privileged data
can be made available to processes running under a dynamic UID (i.e. not a previously known one)
without having to open up access to all users.In order to reference the path a credential may be read from within a
ExecStart= command line use ${CREDENTIALS_DIRECTORY}/mycred,
e.g. ExecStart=cat ${CREDENTIALS_DIRECTORY}/mycred.Currently, an accumulated credential size limit of 1M bytes per unit is
enforced.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 getpeername2
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.SetCredential=ID:VALUEThe SetCredential= setting is similar to
LoadCredential= but accepts a literal value to use as data for the credential,
instead of a file system path to read the data from. Do not use this option for data that is supposed
to be secret, as it is accessible to unprivileged processes via IPC. It's only safe to use this for
user IDs, public key material and similar non-sensitive data. For everything else use
LoadCredential=. In order to embed binary data into the credential data use
C-style escaping (i.e. \n to embed a newline, or \x00 to embed
a NUL byte).If a credential of the same ID is listed in both LoadCredential= and
SetCredential=, the latter will act as default if the former cannot be
retrieved. In this case not being able to retrieve the credential from the path specified in
LoadCredential= is not considered fatal.System V CompatibilityUtmpIdentifier=Takes a four character identifier string for an utmp5 and wtmp entry
for this service. This should only be set for services such as getty implementations (such
as agetty8) where utmp/wtmp
entries must be created and cleared before and after execution, or for services that shall be executed as if
they were run by a getty process (see below). If the configured string is longer than four
characters, it is truncated and the terminal four characters are used. This setting interprets %I style string
replacements. This setting is unset by default, i.e. no utmp/wtmp entries are created or cleaned up for this
service.UtmpMode=Takes one of init, login or user. If
UtmpIdentifier= is set, controls which type of utmp5/wtmp entries
for this service are generated. This setting has no effect unless UtmpIdentifier= is set
too. If init is set, only an INIT_PROCESS entry is generated and the
invoked process must implement a getty-compatible utmp/wtmp logic. If
login is set, first an INIT_PROCESS entry, followed by a
LOGIN_PROCESS entry is generated. In this case, the invoked process must implement a
login1-compatible
utmp/wtmp logic. If user is set, first an INIT_PROCESS entry, then a
LOGIN_PROCESS entry and finally a USER_PROCESS entry is
generated. In this case, the invoked process may be any process that is suitable to be run as session
leader. Defaults to init.Environment variables in spawned processesProcesses started by the service manager are executed with an environment variable block assembled from
multiple sources. Processes started by the system service manager generally do not inherit environment variables
set for the service manager itself (but this may be altered via PassEnvironment=), but processes
started by the user service manager instances generally do inherit all environment variables set for the service
manager itself.For each invoked process the list of environment variables set is compiled from the following sources:Variables globally configured for the service manager, using the
DefaultEnvironment= setting in
systemd-system.conf5, the kernel command line option systemd.setenv= (see
systemd1) or via
systemctl set-environment (see systemctl1).Variables defined by the service manager itself (see the list below)Variables set in the service manager's own environment variable block (subject to PassEnvironment= for the system service manager)Variables set via Environment= in the unit fileVariables read from files specified via EnvironmentFile= in the unit fileVariables set by any PAM modules in case PAMName= is in effect,
cf. pam_env8If the same environment variables are set by multiple of these sources, the later source — according to the
order of the list above — wins. Note that as final step all variables listed in
UnsetEnvironment= are removed again from the compiled environment variable list, immediately
before it is passed to the executed process.The following environment variables are set or propagated by the service manager for each invoked
process:$PATHColon-separated list of directories to use when launching
executables. systemd uses a fixed value of
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
in the system manager. When compiled for systems with "unmerged /usr" (/bin is
not a symlink to /usr/bin),
:/sbin:/bin is appended. In case of the
the user manager, a different path may be configured by the distribution. It is recommended to not
rely on the order of entries, and have only one program with a given name in
$PATH.$LANGLocale. Can be set in
locale.conf5
or on the kernel command line (see
systemd1
and
kernel-command-line7).
$USER$LOGNAME$HOME$SHELLUser name (twice), home directory, and the
login shell. The variables are set for the units that have
User= set, which includes user
systemd instances. See
passwd5.
$INVOCATION_IDContains a randomized, unique 128bit ID identifying each runtime cycle of the unit, formatted
as 32 character hexadecimal string. A new ID is assigned each time the unit changes from an inactive state into
an activating or active state, and may be used to identify this specific runtime cycle, in particular in data
stored offline, such as the journal. The same ID is passed to all processes run as part of the
unit.$XDG_RUNTIME_DIRThe directory to use for runtime objects (such as IPC objects) and volatile state. Set for all
services run by the user systemd instance, as well as any system services that use
PAMName= with a PAM stack that includes pam_systemd. See below and
pam_systemd8 for more
information.$RUNTIME_DIRECTORY$STATE_DIRECTORY$CACHE_DIRECTORY$LOGS_DIRECTORY$CONFIGURATION_DIRECTORYAbsolute paths to the directories defined with
RuntimeDirectory=, StateDirectory=,
CacheDirectory=, LogsDirectory=, and
ConfigurationDirectory= when those settings are used.$CREDENTIALS_DIRECTORYAn absolute path to the per-unit directory with credentials configured via
LoadCredential=/SetCredential=. The directory is marked
read-only and is placed in unswappable memory (if supported and permitted), and is only accessible to
the UID associated with the unit via User= or DynamicUser= (and
the superuser).$MAINPIDThe PID of the unit's main process if it is
known. This is only set for control processes as invoked by
ExecReload= and similar. $MANAGERPIDThe PID of the user systemd
instance, set for processes spawned by it. $LISTEN_FDS$LISTEN_PID$LISTEN_FDNAMESInformation about file descriptors passed to a
service for socket activation. See
sd_listen_fds3.
$NOTIFY_SOCKETThe socket
sd_notify() talks to. See
sd_notify3.
$WATCHDOG_PID$WATCHDOG_USECInformation about watchdog keep-alive notifications. See
sd_watchdog_enabled3.
$TERMTerminal type, set only for units connected to
a terminal (StandardInput=tty,
StandardOutput=tty, or
StandardError=tty). See
termcap5.
$LOG_NAMESPACEContains the name of the selected logging namespace when the
LogNamespace= service setting is used.$JOURNAL_STREAMIf the standard output or standard error output of the executed processes are connected to the
journal (for example, by setting StandardError=journal) $JOURNAL_STREAM
contains the device and inode numbers of the connection file descriptor, formatted in decimal, separated by a
colon (:). This permits invoked processes to safely detect whether their standard output or
standard error output are connected to the journal. The device and inode numbers of the file descriptors should
be compared with the values set in the environment variable to determine whether the process output is still
connected to the journal. Note that it is generally not sufficient to only check whether
$JOURNAL_STREAM is set at all as services might invoke external processes replacing their
standard output or standard error output, without unsetting the environment variable.If both standard output and standard error of the executed processes are connected to the journal via a
stream socket, this environment variable will contain information about the standard error stream, as that's
usually the preferred destination for log data. (Note that typically the same stream is used for both standard
output and standard error, hence very likely the environment variable contains device and inode information
matching both stream file descriptors.)This environment variable is primarily useful to allow services to optionally upgrade their used log
protocol to the native journal protocol (using
sd_journal_print3 and other
functions) if their standard output or standard error output is connected to the journal anyway, thus enabling
delivery of structured metadata along with logged messages.$SERVICE_RESULTOnly defined for the service unit type, this environment variable is passed to all
ExecStop= and ExecStopPost= processes, and encodes the service
"result". Currently, the following values are defined:
Defined $SERVICE_RESULT valuesValueMeaningsuccessThe service ran successfully and exited cleanly.protocolA protocol violation occurred: the service did not take the steps required by its unit configuration (specifically what is configured in its Type= setting).timeoutOne of the steps timed out.exit-codeService process exited with a non-zero exit code; see $EXIT_CODE below for the actual exit code returned.signalA service process was terminated abnormally by a signal, without dumping core. See $EXIT_CODE below for the actual signal causing the termination.core-dumpA service process terminated abnormally with a signal and dumped core. See $EXIT_CODE below for the signal causing the termination.watchdogWatchdog keep-alive ping was enabled for the service, but the deadline was missed.start-limit-hitA start limit was defined for the unit and it was hit, causing the unit to fail to start. See systemd.unit5's StartLimitIntervalSec= and StartLimitBurst= for details.resourcesA catch-all condition in case a system operation failed.
This environment variable is useful to monitor failure or successful termination of a service. Even
though this variable is available in both ExecStop= and ExecStopPost=, it
is usually a better choice to place monitoring tools in the latter, as the former is only invoked for services
that managed to start up correctly, and the latter covers both services that failed during their start-up and
those which failed during their runtime.$EXIT_CODE$EXIT_STATUSOnly defined for the service unit type, these environment variables are passed to all
ExecStop=, ExecStopPost= processes and contain exit status/code
information of the main process of the service. For the precise definition of the exit code and status, see
wait2. $EXIT_CODE
is one of exited, killed,
dumped. $EXIT_STATUS contains the numeric exit code formatted as string
if $EXIT_CODE is exited, and the signal name in all other cases. Note
that these environment variables are only set if the service manager succeeded to start and identify the main
process of the service.
Summary of possible service result variable values$SERVICE_RESULT$EXIT_CODE$EXIT_STATUSsuccesskilledHUP, INT, TERM, PIPEexited0protocolnot setnot setexited0timeoutkilledTERM, KILLexited0, 1, 2, 3, …, 255exit-codeexited1, 2, 3, …, 255signalkilledHUP, INT, KILL, …core-dumpdumpedABRT, SEGV, QUIT, …watchdogdumpedABRTkilledTERM, KILLexited0, 1, 2, 3, …, 255exec-conditionexited1, 2, 3, 4, …, 254oom-killkilledTERM, KILLstart-limit-hitnot setnot setresourcesany of the aboveany of the aboveNote: the process may be also terminated by a signal not sent by systemd. In particular the process may send an arbitrary signal to itself in a handler for any of the non-maskable signals. Nevertheless, in the timeout and watchdog rows above only the signals that systemd sends have been included. Moreover, using SuccessExitStatus= additional exit statuses may be declared to indicate clean termination, which is not reflected by this table.
$PIDFILEThe path to the configured PID file, in case the process is forked off on behalf of a
service that uses the PIDFile= setting, see
systemd.service5
for details. Service code may use this environment variable to automatically generate a PID file at
the location configured in the unit file. This field is set to an absolute path in the file
system.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_systemd8 for details.Process exit codesWhen 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 fork2 system call, but
before the matching execve2 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.
Basic C library exit codesExit CodeSymbolic NameDescription0EXIT_SUCCESSGeneric success code.1EXIT_FAILUREGeneric failure or unspecified error.
The following service exit codes are defined by the LSB specification.
LSB service exit codesExit CodeSymbolic NameDescription2EXIT_INVALIDARGUMENTInvalid or excess arguments.3EXIT_NOTIMPLEMENTEDUnimplemented feature.4EXIT_NOPERMISSIONThe user has insufficient privileges.5EXIT_NOTINSTALLEDThe program is not installed.6EXIT_NOTCONFIGUREDThe program is not configured.7EXIT_NOTRUNNINGThe program is not running.
The LSB specification suggests that error codes 200 and above are reserved for implementations. Some of them are
used by the service manager to indicate problems during process invocation:
systemd-specific exit codesExit CodeSymbolic NameDescription200EXIT_CHDIRChanging to the requested working directory failed. See WorkingDirectory= above.201EXIT_NICEFailed to set up process scheduling priority (nice level). See Nice= above.202EXIT_FDSFailed to close unwanted file descriptors, or to adjust passed file descriptors.203EXIT_EXECThe actual process execution failed (specifically, the execve2 system call). Most likely this is caused by a missing or non-accessible executable file.204EXIT_MEMORYFailed to perform an action due to memory shortage.205EXIT_LIMITSFailed to adjust resource limits. See LimitCPU= and related settings above.206EXIT_OOM_ADJUSTFailed to adjust the OOM setting. See OOMScoreAdjust= above.207EXIT_SIGNAL_MASKFailed to set process signal mask.208EXIT_STDINFailed to set up standard input. See StandardInput= above.209EXIT_STDOUTFailed to set up standard output. See StandardOutput= above.210EXIT_CHROOTFailed to change root directory (chroot2). See RootDirectory=/RootImage= above.211EXIT_IOPRIOFailed to set up IO scheduling priority. See IOSchedulingClass=/IOSchedulingPriority= above.212EXIT_TIMERSLACKFailed to set up timer slack. See TimerSlackNSec= above.213EXIT_SECUREBITSFailed to set process secure bits. See SecureBits= above.214EXIT_SETSCHEDULERFailed to set up CPU scheduling. See CPUSchedulingPolicy=/CPUSchedulingPriority= above.215EXIT_CPUAFFINITYFailed to set up CPU affinity. See CPUAffinity= above.216EXIT_GROUPFailed to determine or change group credentials. See Group=/SupplementaryGroups= above.217EXIT_USERFailed to determine or change user credentials, or to set up user namespacing. See User=/PrivateUsers= above.218EXIT_CAPABILITIESFailed to drop capabilities, or apply ambient capabilities. See CapabilityBoundingSet=/AmbientCapabilities= above.219EXIT_CGROUPSetting up the service control group failed.220EXIT_SETSIDFailed to create new process session.221EXIT_CONFIRMExecution has been cancelled by the user. See the systemd.confirm_spawn= kernel command line setting on kernel-command-line7 for details.222EXIT_STDERRFailed to set up standard error output. See StandardError= above.224EXIT_PAMFailed to set up PAM session. See PAMName= above.225EXIT_NETWORKFailed to set up network namespacing. See PrivateNetwork= above.226EXIT_NAMESPACEFailed to set up mount namespacing. See ReadOnlyPaths= and related settings above.227EXIT_NO_NEW_PRIVILEGESFailed to disable new privileges. See NoNewPrivileges=yes above.228EXIT_SECCOMPFailed to apply system call filters. See SystemCallFilter= and related settings above.229EXIT_SELINUX_CONTEXTDetermining or changing SELinux context failed. See SELinuxContext= above.230EXIT_PERSONALITYFailed to set up an execution domain (personality). See Personality= above.231EXIT_APPARMOR_PROFILEFailed to prepare changing AppArmor profile. See AppArmorProfile= above.232EXIT_ADDRESS_FAMILIESFailed to restrict address families. See RestrictAddressFamilies= above.233EXIT_RUNTIME_DIRECTORYSetting up runtime directory failed. See RuntimeDirectory= and related settings above.235EXIT_CHOWNFailed to adjust socket ownership. Used for socket units only.236EXIT_SMACK_PROCESS_LABELFailed to set SMACK label. See SmackProcessLabel= above.237EXIT_KEYRINGFailed to set up kernel keyring.238EXIT_STATE_DIRECTORYFailed to set up unit's state directory. See StateDirectory= above.239EXIT_CACHE_DIRECTORYFailed to set up unit's cache directory. See CacheDirectory= above.240EXIT_LOGS_DIRECTORYFailed to set up unit's logging directory. See LogsDirectory= above.241EXIT_CONFIGURATION_DIRECTORYFailed to set up unit's configuration directory. See ConfigurationDirectory= above.242EXIT_NUMA_POLICYFailed to set up unit's NUMA memory policy. See NUMAPolicy= and NUMAMask= above.243EXIT_CREDENTIALSFailed to set up unit's credentials. See LoadCredential= and SetCredential= above.
Finally, the BSD operating systems define a set of exit codes, typically defined on Linux systems too:
BSD exit codesExit CodeSymbolic NameDescription64EX_USAGECommand line usage error65EX_DATAERRData format error66EX_NOINPUTCannot open input67EX_NOUSERAddressee unknown68EX_NOHOSTHost name unknown69EX_UNAVAILABLEService unavailable70EX_SOFTWAREinternal software error71EX_OSERRSystem error (e.g., can't fork)72EX_OSFILECritical OS file missing73EX_CANTCREATCan't create (user) output file74EX_IOERRInput/output error75EX_TEMPFAILTemporary failure; user is invited to retry76EX_PROTOCOLRemote error in protocol77EX_NOPERMPermission denied78EX_CONFIGConfiguration error