SYSTEMD.EXEC(5) systemd.exec SYSTEMD.EXEC(5)
NAME
systemd.exec - Execution environment configuration
SYNOPSIS
service.service, socket.socket, mount.mount, swap.swap
DESCRIPTION
Unit configuration files for services, sockets, mount points, and swap
devices share a subset of configuration options which define the
execution environment of spawned processes.
This man page lists the configuration options shared by these four unit
types. See systemd.unit(5) for the common options of all unit
configuration files, and systemd.service(5), systemd.socket(5),
systemd.swap(5), and systemd.mount(5) for more information on the
specific unit configuration files. The execution specific configuration
options are configured in the [Service], [Socket], [Mount], or [Swap]
sections, depending on the unit type.
In addition, options which control resources through Linux Control
Groups (cgroups) are listed in systemd.resource-control(5). Those
options complement options listed here.
IMPLICIT DEPENDENCIES
A few execution parameters result in additional, automatic dependencies
to be added:
o 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=.
o Similar, units with PrivateTmp= enabled automatically get mount
unit dependencies for all mounts required to access /tmp and
/var/tmp. They will also gain an automatic After= dependency on
systemd-tmpfiles-setup.service(8).
o Units whose standard output or error output is connected to journal
or kmsg (or their combinations with console output, see below)
automatically acquire dependencies of type After= on
systemd-journald.socket.
o Units using LogNamespace= will automatically gain ordering and
requirement dependencies on the two socket units associated with
systemd-journald@.service instances.
PATHS
The following settings may be used to change a service's view of the
filesystem. Please note that the paths must be absolute and must not
contain a ".." path component.
WorkingDirectory=
Takes a directory path relative to the service's root directory
specified by RootDirectory=, or the special value "~". Sets the
working directory for executed processes. If set to "~", the home
directory of the user specified in User= is used. If not set,
defaults to the root directory when systemd is running as a system
instance and the respective user's home directory if run as user.
If the setting is prefixed with the "-" character, a missing
working directory is not considered fatal. If
RootDirectory=/RootImage= is not set, then WorkingDirectory= is
relative to the root of the system running the service manager.
Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).
RootDirectory=
Takes a directory path relative to the host's root directory (i.e.
the root of the system running the service manager). Sets the root
directory for executed processes, with the chroot(2) system call.
If this is used, it must be ensured that the process binary and all
its auxiliary files are available in the chroot() jail. Note that
setting this parameter might result in additional dependencies to
be added to the unit (see above).
The MountAPIVFS= and PrivateUsers= settings are particularly useful
in conjunction with RootDirectory=. For details, see below.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
RootImage=
Takes a path to a block device node or regular file as argument.
This call is similar to RootDirectory= however mounts a file system
hierarchy from a block device node or loopback file instead of a
directory. The device node or file system image file needs to
contain a file system without a partition table, or a file system
within an MBR/MS-DOS or GPT partition table with only a single
Linux-compatible partition, or a set of file systems within a GPT
partition table that follows the Discoverable Partitions
Specification[1].
When DevicePolicy= is set to "closed" or "strict", or set to "auto"
and DeviceAllow= is set, then this setting adds /dev/loop-control
with rw mode, "block-loop" and "block-blkext" with rwm mode to
DeviceAllow=. See systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as
it may change the setting of DevicePolicy=.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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=.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
CREDENTIALS
These options are only available for system services and are not
supported for services running in per-user instances of the service
manager.
User=, Group=
Set the UNIX user or group that the processes are executed as,
respectively. Takes a single user or group name, or a numeric ID as
argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root
user (services managed by root's instance of systemd --user), the
default is "root", but User= may be used to specify a different
user. For user services of any other user, switching user identity
is not permitted, hence the only valid setting is the same user the
user's service manager is running as. If no group is set, the
default group of the user is used. This setting does not affect
commands whose command line is prefixed with "+".
Note that this enforces only weak restrictions on the user/group
name syntax, but will generate warnings in many cases where
user/group names do not adhere to the following rules: the
specified name should consist only of the characters a-z, A-Z, 0-9,
"_" and "-", except for the first character which must be one of
a-z, A-Z and "_" (i.e. digits and "-" are not permitted as first
character). The user/group name must have at least one character,
and at most 31. These restrictions are made in order to avoid
ambiguities and to ensure user/group names and unit files remain
portable among Linux systems. For further details on the names
accepted and the names warned about see User/Group Name Syntax[2].
When used in conjunction with DynamicUser= the user/group name
specified is dynamically allocated at the time the service is
started, and released at the time the service is stopped -- unless
it is already allocated statically (see below). If DynamicUser= is
not used the specified user and group must have been created
statically in the user database no later than the moment the
service is started, for example using the sysusers.d(5) facility,
which is applied at boot or package install time. If the user does
not exist by then program invocation will fail.
If the User= setting is used the supplementary group list is
initialized from the specified user's default group list, as
defined in the system's user and group database. Additional groups
may be configured through the SupplementaryGroups= setting (see
below).
DynamicUser=
Takes a boolean parameter. If set, a UNIX user and group pair is
allocated dynamically when the unit is started, and released as
soon as it is stopped. The user and group will not be added to
/etc/passwd or /etc/group, but are managed transiently during
runtime. The nss-systemd(8) glibc NSS module provides integration
of these dynamic users/groups into the system's user and group
databases. The user and group name to use may be configured via
User= and Group= (see above). If these options are not used and
dynamic user/group allocation is enabled for a unit, the name of
the dynamic user/group is implicitly derived from the unit name. If
the unit name without the type suffix qualifies as valid user name
it is used directly, otherwise a name incorporating a hash of it is
used. If a statically allocated user or group of the configured
name already exists, it is used and no dynamic user/group is
allocated. Note that if User= is specified and the static group
with the name exists, then it is required that the static user with
the name already exists. Similarly, if Group= is specified and the
static user with the name exists, then it is required that the
static group with the name already exists. Dynamic users/groups are
allocated from the UID/GID range 61184...65519. It is recommended
to avoid this range for regular system or login users. At any point
in time each UID/GID from this range is only assigned to zero or
one dynamically allocated users/groups in use. However, UID/GIDs
are recycled after a unit is terminated. Care should be taken that
any processes running as part of a unit for which dynamic
users/groups are enabled do not leave files or directories owned by
these users/groups around, as a different unit might get the same
UID/GID assigned later on, and thus gain access to these files or
directories. If DynamicUser= is enabled, RemoveIPC= and PrivateTmp=
are implied (and cannot be turned off). This ensures that the
lifetime of IPC objects and temporary files created by the executed
processes is bound to the runtime of the service, and hence the
lifetime of the dynamic user/group. Since /tmp/ and /var/tmp/ are
usually the only world-writable directories on a system this
ensures that a unit making use of dynamic user/group allocation
cannot leave files around after unit termination. Furthermore
NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled (and
cannot be disabled), to ensure that processes invoked cannot take
benefit or create SUID/SGID files or directories. Moreover
ProtectSystem=strict and ProtectHome=read-only are implied, thus
prohibiting the service to write to arbitrary file system
locations. In order to allow the service to write to certain
directories, they have to be whitelisted 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 pam(8) for details.
Note that for each unit making use of this option a PAM session
handler process will be maintained as part of the unit and stays
around as long as the unit is active, to ensure that appropriate
actions can be taken when the unit and hence the PAM session
terminates. This process is named "(sd-pam)" and is an immediate
child process of the unit's main process.
Note that when this option is used for a unit it is very likely
(depending on PAM configuration) that the main unit process will be
migrated to its own session scope unit when it is activated. This
process will hence be associated with two units: the unit it was
originally started from (and for which PAMName= was configured),
and the session scope unit. Any child processes of that process
will however be associated with the session scope unit only. This
has implications when used in combination with NotifyAccess=all, as
these child processes will not be able to affect changes in the
original unit through notification messages. These messages will be
considered belonging to the session scope unit and not the original
unit. It is hence not recommended to use PAMName= in combination
with NotifyAccess=all.
CAPABILITIES
These options are only available for system services and are not
supported for services running in per-user instances of the service
manager.
CapabilityBoundingSet=
Controls which capabilities to include in the capability bounding
set for the executed process. See capabilities(7) for details.
Takes a whitespace-separated list of capability names, e.g.
CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities
listed will be included in the bounding set, all others are
removed. If the list of capabilities is prefixed with "~", all but
the listed capabilities will be included, the effect of the
assignment inverted. Note that this option also affects the
respective capabilities in the effective, permitted and inheritable
capability sets. If this option is not used, the capability
bounding set is not modified on process execution, hence no limits
on the capabilities of the process are enforced. This option may
appear more than once, in which case the bounding sets are merged
by OR, or by AND if the lines are prefixed with "~" (see below). If
the empty string is assigned to this option, the bounding set is
reset to the empty capability set, and all prior settings have no
effect. If set to "~" (without any further argument), the bounding
set is reset to the full set of available capabilities, also
undoing any previous settings. This does not affect commands
prefixed with "+".
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 "+".
SECURITY
NoNewPrivileges=
Takes a boolean argument. If true, ensures that the service process
and all its children can never gain new privileges through execve()
(e.g. via setuid or setgid bits, or filesystem capabilities). This
is the simplest and most effective way to ensure that a process and
its children can never elevate privileges again. Defaults to false,
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[3].
SecureBits=
Controls the secure bits set for the executed process. Takes a
space-separated combination of options from the following list:
keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot, and noroot-locked. This option may
appear more than once, in which case the secure bits are ORed. If
the empty string is assigned to this option, the bits are reset to
0. This does not affect commands prefixed with "+". See
capabilities(7) for details.
MANDATORY ACCESS CONTROL
These options are only available for system services and are not
supported for services running in per-user instances of the service
manager.
SELinuxContext=
Set the SELinux security context of the executed process. If set,
this will override the automated domain transition. However, the
policy still needs to authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by "-", all errors will
be ignored. This does not affect commands prefixed with "+". See
setexeccon(3) 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. This result in a non
operation if AppArmor is not enabled. If prefixed by "-", all
errors will be ignored. This does not affect commands prefixed with
"+".
SmackProcessLabel=
Takes a SMACK64 security label as argument. The process executed by
the unit will be started under this label and SMACK will decide
whether the process is allowed to run or not, based on it. The
process will continue to run under the label specified here unless
the executable has its own SMACK64EXEC label, in which case the
process will transition to run under that label. When not
specified, the label that systemd is running under is used. This
directive is ignored if SMACK is disabled.
The value may be prefixed by "-", in which case all errors will be
ignored. An empty value may be specified to unset previous
assignments. This does not affect commands prefixed with "+".
PROCESS PROPERTIES
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=,
LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=,
LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=,
LimitRTTIME=
Set soft and hard limits on various resources for executed
processes. See setrlimit(2) for details on the 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 soft:hard to set both limits
individually (e.g. "LimitAS=4G:16G"). Use the string infinity to
configure no limit on a specific resource. The multiplicative
suffixes K, M, G, T, P and E (to the base 1024) may be used for
resource limits measured in bytes (e.g. "LimitAS=16G"). For the
limits referring to time values, the usual time units ms, s, min, h
and so on may be used (see systemd.time(7) for details). Note that
if no time unit is specified for LimitCPU= the default unit of
seconds is implied, while for LimitRTTIME= the default unit of
microseconds is implied. Also, note that the effective granularity
of the limits might influence their enforcement. For example, time
limits specified for LimitCPU= will be rounded up implicitly to
multiples of 1s. For LimitNICE= the value may be specified in two
syntaxes: if prefixed with "+" or "-", the value is understood as
regular Linux nice value in the range -20..19. If not prefixed like
this the value is understood as raw resource limit parameter in the
range 0..40 (with 0 being equivalent to 1).
Note that most process resource limits configured with these
options are per-process, and processes may fork in order to acquire
a new set of resources that are accounted independently of the
original process, and may thus escape limits set. Also note that
LimitRSS= is not implemented on Linux, and setting it has no
effect. Often it is advisable to prefer the resource controls
listed in systemd.resource-control(5) over these per-process
limits, as they apply to services as a whole, may be altered
dynamically at runtime, and are generally more expressive. For
example, MemoryMax= is a more powerful (and working) replacement
for LimitRSS=.
Resource limits not configured explicitly for a unit default to the
value configured in the various DefaultLimitCPU=,
DefaultLimitFSIZE=, ... options available in systemd-
system.conf(5), and - if not configured there - the kernel or
per-user defaults, as defined by the OS (the latter only for user
services, see below).
For system units these resource limits may be chosen freely. When
these settings are configured in a user service (i.e. a service run
by the per-user instance of the service manager) they cannot be
used to raise the limits above those set for the user manager
itself when it was first invoked, as the user's service manager
generally lacks the privileges to do so. In user context these
configuration options are hence only useful to lower the limits
passed in or to raise the soft limit to the maximum of the hard
limit as configured for the user. To raise the user's limits
further, the available configuration mechanisms differ between
operating systems, but typically require privileges. In most cases
it is possible to configure higher per-user resource limits via PAM
or by setting limits on the system service encapsulating the user's
service manager, i.e. the user's instance of user@.service. After
making such changes, make sure to restart the user's service
manager.
Table 1. Resource limit directives, their equivalent ulimit shell
commands and the unit used
+-----------------+-------------------+---------------------+
|Directive | ulimit equivalent | Unit |
+-----------------+-------------------+---------------------+
|LimitCPU= | ulimit -t | Seconds |
+-----------------+-------------------+---------------------+
|LimitFSIZE= | ulimit -f | Bytes |
+-----------------+-------------------+---------------------+
|LimitDATA= | ulimit -d | Bytes |
+-----------------+-------------------+---------------------+
|LimitSTACK= | ulimit -s | Bytes |
+-----------------+-------------------+---------------------+
|LimitCORE= | ulimit -c | Bytes |
+-----------------+-------------------+---------------------+
|LimitRSS= | ulimit -m | Bytes |
+-----------------+-------------------+---------------------+
|LimitNOFILE= | ulimit -n | Number of File |
| | | Descriptors |
+-----------------+-------------------+---------------------+
|LimitAS= | ulimit -v | Bytes |
+-----------------+-------------------+---------------------+
|LimitNPROC= | ulimit -u | Number of Processes |
+-----------------+-------------------+---------------------+
|LimitMEMLOCK= | ulimit -l | Bytes |
+-----------------+-------------------+---------------------+
|LimitLOCKS= | ulimit -x | Number of Locks |
+-----------------+-------------------+---------------------+
|LimitSIGPENDING= | ulimit -i | Number of Queued |
| | | Signals |
+-----------------+-------------------+---------------------+
|LimitMSGQUEUE= | ulimit -q | Bytes |
+-----------------+-------------------+---------------------+
|LimitNICE= | ulimit -e | Nice Level |
+-----------------+-------------------+---------------------+
|LimitRTPRIO= | ulimit -r | Realtime Priority |
+-----------------+-------------------+---------------------+
|LimitRTTIME= | No equivalent | Microseconds |
+-----------------+-------------------+---------------------+
UMask=
Controls the file mode creation mask. Takes an access mode in octal
notation. See umask(2) for details. Defaults to 0022 for system
units. For units of the user service manager the default value is
inherited from the user instance (whose default is inherited from
the system service manager, and thus also is 0022). Hence changing
the default value of a user instance, either via UMask= or via a
PAM module, will affect the user instance itself and all user units
started by the user instance unless a user unit has specified its
own UMask=.
KeyringMode=
Controls how the kernel session keyring is set up for the service
(see session-keyring(7) for details on the session keyring). Takes
one of inherit, private, shared. If set to inherit no special
keyring setup is done, and the kernel's default behaviour is
applied. If private is used a new session keyring is allocated when
a service process is invoked, and it is not linked up with any user
keyring. This is the recommended setting for system services, as
this ensures that multiple services running under the same system
user ID (in particular the root user) do not share their key
material among each other. If shared is used a new session keyring
is allocated as for private, but the user keyring of the user
configured with User= is linked into it, so that keys assigned to
the user may be requested by the unit's processes. In this modes
multiple units running processes under the same user ID may share
key material. Unless inherit is selected the unique invocation ID
for the unit (see below) is added as a protected key by the name
"invocation_id" to the newly created session keyring. Defaults to
private for services of the system service manager and to inherit
for non-service units and for services of the user service manager.
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[4] 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.service(5) for details.
TimerSlackNSec=
Sets the timer slack in nanoseconds for the executed processes. The
timer slack controls the accuracy of wake-ups triggered by timers.
See prctl(2) for more information. Note that in contrast to most
other time span definitions this parameter takes an integer value
in nano-seconds if no unit is specified. The usual time units are
understood too.
Personality=
Controls which kernel architecture uname(2) shall report, when
invoked by unit processes. Takes one of the architecture
identifiers 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.
SCHEDULING
Nice=
Sets the default nice level (scheduling priority) for executed
processes. Takes an integer between -20 (highest priority) and 19
(lowest priority). See setpriority(2) for details.
CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed processes. Takes one of
other, batch, idle, fifo or rr. See sched_setscheduler(2) for
details.
CPUSchedulingPriority=
Sets the CPU scheduling priority for executed processes. The
available priority range depends on the selected CPU scheduling
policy (see above). For real-time scheduling policies an integer
between 1 (lowest priority) and 99 (highest priority) can be used.
See sched_setscheduler(2) for details.
CPUSchedulingResetOnFork=
Takes a boolean argument. If true, elevated CPU scheduling
priorities and policies will be reset when the executed processes
fork, and can hence not leak into child processes. See
sched_setscheduler(2) for details. Defaults to false.
CPUAffinity=
Controls the CPU affinity of the executed processes. Takes a list
of CPU indices or ranges separated by either whitespace or commas.
Alternatively, takes a special "numa" value in which case systemd
automatically derives allowed CPU range based on the value of
NUMAMask= option. CPU ranges are specified by the lower and upper
CPU indices separated by a dash. This option may be specified more
than once, in which case the specified CPU affinity masks are
merged. If the empty string is assigned, the mask is reset, all
assignments prior to this will have no effect. See
sched_setaffinity(2) for details.
NUMAPolicy=
Controls the NUMA memory policy of the executed processes. Takes a
policy type, one of: default, preferred, bind, interleave and
local. A list of NUMA nodes that should be associated with the
policy must be specified in NUMAMask=. For more details on each
policy please see, set_mempolicy(2). For overall overview of NUMA
support in Linux see, numa(7)
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. Note that the
list of NUMA nodes is not required for default and local policies
and for preferred policy we expect a single NUMA node.
IOSchedulingClass=
Sets the I/O scheduling class for executed processes. Takes an
integer between 0 and 3 or one of the strings none, realtime,
best-effort or idle. If the empty string is assigned to this
option, all prior assignments to both IOSchedulingClass= and
IOSchedulingPriority= have no effect. See ioprio_set(2) for
details.
IOSchedulingPriority=
Sets the I/O scheduling priority for executed processes. Takes an
integer between 0 (highest priority) and 7 (lowest priority). 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_set(2) for
details.
SANDBOXING
The following sandboxing options are an effective way to limit the
exposure of the system towards the unit's processes. It is recommended
to turn on as many of these options for each unit as is possible
without negatively affecting the process' ability to operate. Note that
many of these sandboxing features are gracefully turned off on systems
where the underlying security mechanism is not available. For example,
ProtectSystem= has no effect if the kernel is built without file system
namespacing or if the service manager runs in a container manager that
makes file system namespacing unavailable to its payload. 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=true.
ProtectSystem=
Takes a boolean argument or the special values "full" or "strict".
If true, mounts the /usr and the boot loader directories (/boot and
/efi) read-only for processes invoked by this unit. If set to
"full", the /etc directory is mounted read-only, too. If set to
"strict" the entire file system hierarchy is mounted read-only,
except for the API file system subtrees /dev, /proc and /sys
(protect these directories using PrivateDevices=,
ProtectKernelTunables=, ProtectControlGroups=). This setting
ensures that any modification of the vendor-supplied operating
system (and optionally its configuration, and local mounts) is
prohibited for the service. It is recommended to enable this
setting for all long-running services, unless they are involved
with system updates or need to modify the operating system in other
ways. If this option is used, ReadWritePaths= may be used to
exclude specific directories from being made read-only. This
setting is implied if DynamicUser= is set. This setting cannot
ensure protection in all cases. In general it has the same
limitations as ReadOnlyPaths=, see below. Defaults to off.
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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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, one or more directories by the specified names will
be created (including their parents) below the locations defined in
the following table, when the unit is started. Also, the
corresponding environment variable is defined with the full path of
directories. If multiple directories are set, then in the
environment variable the paths are concatenated with colon (":").
Table 2. Automatic directory creation and environment variables
+------------------------+----------------+-----------------------+--------------------------+
|Directory | Below path for | Below path for | Environment |
| | system units | user units | variable set |
+------------------------+----------------+-----------------------+--------------------------+
|RuntimeDirectory= | /run/ | $XDG_RUNTIME_DIR | $RUNTIME_DIRECTORY |
+------------------------+----------------+-----------------------+--------------------------+
|StateDirectory= | /var/lib/ | $XDG_CONFIG_HOME | $STATE_DIRECTORY |
+------------------------+----------------+-----------------------+--------------------------+
|CacheDirectory= | /var/cache/ | $XDG_CACHE_HOME | $CACHE_DIRECTORY |
+------------------------+----------------+-----------------------+--------------------------+
|LogsDirectory= | /var/log/ | $XDG_CONFIG_HOME/log/ | $LOGS_DIRECTORY |
+------------------------+----------------+-----------------------+--------------------------+
|ConfigurationDirectory= | /etc/ | $XDG_CONFIG_HOME | $CONFIGURATION_DIRECTORY |
+------------------------+----------------+-----------------------+--------------------------+
In case of RuntimeDirectory= the innermost subdirectories are
removed when the unit is stopped. It is possible to preserve the
specified directories in this case if RuntimeDirectoryPreserve= is
configured to restart or yes (see below). The directories specified
with StateDirectory=, CacheDirectory=, LogsDirectory=,
ConfigurationDirectory= are not removed when the unit is stopped.
Except in case of ConfigurationDirectory=, the innermost specified
directories will be owned by the user and group specified in User=
and Group=. If the specified directories already exist and their
owning user or group do not match the configured ones, all files
and directories below the specified directories as well as the
directories themselves will have their file ownership recursively
changed to match what is configured. As an optimization, if the
specified directories are already owned by the right user and
group, files and directories below of them are left as-is, even if
they do not match what is requested. The innermost specified
directories will have their access mode adjusted to the what is
specified in RuntimeDirectoryMode=, StateDirectoryMode=,
CacheDirectoryMode=, LogsDirectoryMode= and
ConfigurationDirectoryMode=.
These options imply BindPaths= for the specified paths. When
combined with RootDirectory= or RootImage= these paths always
reside on the host and are mounted from there into the unit's file
system namespace.
If DynamicUser= is used in conjunction with StateDirectory=,
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.d(5).
The directories defined by these options are always created under
the standard paths used by systemd (/var, /run, /etc, ...). If the
service needs directories in a different location, a different
mechanism has to be used to create them.
tmpfiles.d(5) provides functionality that overlaps with these
options. Using these options is recommended, because the lifetime
of the directories is tied directly to the lifetime of the unit,
and it is not necessary to ensure that the tmpfiles.d configuration
is executed before the unit is started.
To remove any of the directories created by these settings, use the
systemctl clean ... command on the relevant units, see
systemctl(1) for details.
Example: if a system service unit has the following,
RuntimeDirectory=foo/bar baz
the service manager creates /run/foo (if it does not exist),
/run/foo/bar, and /run/baz. The directories /run/foo/bar and
/run/baz except /run/foo are owned by the user and group specified
in User= and Group=, and removed when the service is stopped.
Example: if a system service unit has the following,
RuntimeDirectory=foo/bar
StateDirectory=aaa/bbb ccc
then the environment variable "RUNTIME_DIRECTORY" is set with
"/run/foo/bar", and "STATE_DIRECTORY" is set with
"/var/lib/aaa/bbb:/var/lib/ccc".
RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
LogsDirectoryMode=, ConfigurationDirectoryMode=
Specifies the access mode of the directories specified in
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, or ConfigurationDirectory=, respectively, as an
octal number. Defaults to 0755. See "Permissions" in
path_resolution(7) for a discussion of the meaning of permission
bits.
RuntimeDirectoryPreserve=
Takes a boolean argument or restart. If set to no (the default),
the directories specified in RuntimeDirectory= are always removed
when the service stops. If set to restart the directories are
preserved when the service is both automatically and manually
restarted. Here, the automatic restart means the operation
specified in Restart=, and manual restart means the one triggered
by systemctl restart foo.service. If set to yes, then the
directories are not removed when the service is stopped. Note that
since the runtime directory /run is a mount point of "tmpfs", then
for system services the directories specified in RuntimeDirectory=
are removed when the system is rebooted.
TimeoutCleanSec=
Configures a timeout on the clean-up operation requested through
systemctl clean ..., see systemctl(1) for details. Takes the usual
time values and defaults to infinity, i.e. by default no time-out
is applied. If a time-out is configured the clean operation will be
aborted forcibly when the time-out 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 might have to the
file system hierarchy. 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 whitelist 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.
These options are only available for system services and are not
supported for services running in per-user instances of the service
manager.
TemporaryFileSystem=
Takes a space-separated list of mount points for temporary file
systems (tmpfs). If set, a new file system namespace is set up for
executed processes, and a temporary file system is mounted on each
mount point. This option may be specified more than once, in which
case temporary file systems are mounted on all listed mount points.
If the empty string is assigned to this option, the list is reset,
and all prior assignments have no effect. Each mount point may
optionally be suffixed with a colon (":") and mount options such as
"size=10%" or "ro". By default, each temporary file system is
mounted with "nodev,strictatime,mode=0755". These can be disabled
by explicitly specifying the corresponding mount options, e.g.,
"dev" or "nostrictatime".
This is useful to hide files or directories not relevant to the
processes invoked by the unit, while necessary files or directories
can be still accessed by combining with BindPaths= or
BindReadOnlyPaths=:
Example: if a unit has the following,
TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd
then the invoked processes by the unit cannot see any files or
directories under /var except for /var/lib/systemd or its contents.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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 is not shared by processes
outside of the namespace. This is useful to secure access to
temporary files of the process, but makes sharing between processes
via /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.unit(5) for details. This setting is implied if
DynamicUser= is set. For this setting the same restrictions
regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Enabling this setting
has the side effect of adding Requires= and After= dependencies on
all mount units necessary to access /tmp and /var/tmp. Moreover an
implicitly After= ordering on systemd-tmpfiles-setup.service(8) is
added.
Note that the implementation of this setting might be impossible
(for example if mount namespaces are not available), and the unit
should be written in a way that does not solely rely on this
setting for security.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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-
control(5) for details). Note that using this setting will
disconnect propagation of mounts from the service to the host
(propagation in the opposite direction continues to work). This
means that this setting may not be used for services which shall be
able to install mount points in the main mount namespace. The new
/dev will be mounted read-only and 'noexec'. The latter may break
old programs which try to set up executable memory by using mmap(2)
of /dev/zero instead of using MAP_ANON. For this setting the same
restrictions regarding mount propagation and privileges apply as
for ReadOnlyPaths= and related calls, see above. 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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
PrivateNetwork=
Takes a boolean argument. If true, sets up a new network namespace
for the executed processes and configures only the loopback network
device "lo" inside it. No other network devices will be available
to the executed process. This is useful to turn off network access
by the executed process. Defaults to false. It is possible to run
two or more units within the same private network namespace by
using the JoinsNamespaceOf= directive, see systemd.unit(5) for
details. Note that this option will disconnect all socket families
from the host, including AF_NETLINK and AF_UNIX. Effectively, for
AF_NETLINK this means that device configuration events received
from systemd-udevd.service(8) are not delivered to the unit's
processes. And for AF_UNIX this has the effect that AF_UNIX sockets
in the abstract socket namespace of the host will become
unavailable to the unit's processes (however, those located in the
file system will continue to be accessible).
Note that the implementation of this setting might be impossible
(for example if network namespaces are not available), and the unit
should be written in a way that does not solely rely on this
setting for security.
When this option is used on a socket unit any sockets bound on
behalf of this unit will be bound within a private network
namespace. This may be combined with JoinsNamespaceOf= to listen on
sockets inside of network namespaces of other services.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
PrivateUsers=
Takes a boolean argument. If true, sets up a new user namespace for
the executed processes and configures a minimal user and group
mapping, that maps the "root" user and group as well as the unit's
own user and group to themselves and everything else to the
"nobody" user and group. This is useful to securely detach the user
and group databases used by the unit from the rest of the system,
and thus to create an effective sandbox environment. All files,
directories, processes, IPC objects and other resources owned by
users/groups not equaling "root" or the unit's own will stay
visible from within the unit but appear owned by the "nobody" user
and group. If this mode is enabled, all unit processes are run
without privileges in the host user namespace (regardless if the
unit's own user/group is "root" or not). Specifically this means
that the process will have zero process capabilities on the host's
user namespace, but full capabilities within the service's user
namespace. Settings such as CapabilityBoundingSet= will affect only
the latter, and there's no way to acquire additional capabilities
in the host's user namespace. Defaults to off.
When this setting is set up by a per-user instance of the service
manager, the mapping of the "root" user and group to itself is
omitted (unless the user manager is root). Additionally, in the
per-user instance manager case, the user namespace will be set up
before most other namespaces. This means that combining
PrivateUsers=true with other namespaces will enable use of features
not normally supported by the per-user instances of the service
manager.
This setting is particularly useful in conjunction with
RootDirectory=/RootImage=, as the need to synchronize the user and
group databases in the root directory and on the host is reduced,
as the only users and groups who need to be matched are "root",
"nobody" and the unit's own user and group.
Note that the implementation of this setting might be impossible
(for example if user namespaces are not available), and the unit
should be written in a way that does not solely rely on this
setting for security.
ProtectHostname=
Takes a boolean argument. When set, sets up a new UTS namespace for
the executed processes. In addition, changing hostname or
domainname is prevented. Defaults to off.
Note that the implementation of this setting might be impossible
(for example if UTS namespaces are not available), and the unit
should be written in a way that does not solely rely on this
setting for security.
Note that when this option is enabled for a service hostname
changes no longer propagate from the system into the service, it is
hence not suitable for services that need to take notice of system
hostname changes dynamically.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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-control(5) for the details about DeviceAllow=.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
ProtectKernelTunables=
Takes a boolean argument. If true, kernel variables accessible
through /proc/sys, /sys, /proc/sysrq-trigger, /proc/latency_stats,
/proc/acpi, /proc/timer_stats, /proc/fs and /proc/irq will be made
read-only to all processes of the unit. Usually, tunable kernel
variables should be initialized only at boot-time, for example with
the sysctl.d(5) mechanism. Few services need to write to these at
runtime; it is hence recommended to turn this on for most services.
For this setting the same restrictions regarding mount propagation
and privileges apply as for ReadOnlyPaths= and related calls, see
above. Defaults to off. 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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading will be
denied. This allows module load and unload operations to be turned
off on modular kernels. It is recommended to turn this on for most
services that do not need special file systems or extra kernel
modules to work. Defaults to off. Enabling this option removes
CAP_SYS_MODULE from the capability bounding set for the unit, and
installs a system call filter to block module system calls, also
/usr/lib/modules is made inaccessible. For this setting the same
restrictions regarding mount propagation and privileges apply as
for ReadOnlyPaths= and related calls, see above. Note that limited
automatic module loading due to user configuration or kernel
mapping tables might still happen as side effect of requested user
operations, both privileged and unprivileged. To disable module
auto-load feature please see sysctl.d(5) kernel.modules_disabled
mechanism and /proc/sys/kernel/modules_disabled documentation. 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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
ProtectKernelLogs=
Takes a boolean argument. If true, access to the kernel log ring
buffer will be denied. It is recommended to turn this on for most
services that do not need to read from or write to the kernel log
ring buffer. Enabling this option removes CAP_SYSLOG from the
capability bounding set for this unit, and installs a system call
filter to block the syslog(2) system call (not to be confused with
the libc API syslog(3) for userspace logging). The kernel exposes
its log buffer to userspace via /dev/kmsg and /proc/kmsg. If
enabled, these are made inaccessible to all the processes in the
unit.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
ProtectControlGroups=
Takes a boolean argument. If true, the Linux Control Groups
(cgroups(7)) hierarchies accessible through /sys/fs/cgroup will be
made read-only to all processes of the unit. Except for container
managers no services should require write access to the control
groups hierarchies; it is hence recommended to turn this on for
most services. For this setting the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above. Defaults to off. If ProtectControlGroups=
is set, MountAPIVFS=yes is implied.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
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 whitelist, such as AF_UNIX, AF_INET or AF_INET6.
When prefixed with ~ the listed address families will be applied as
blacklist, otherwise as whitelist. Note that this restricts access
to the socket(2) system call only. Sockets passed into the process
by other means (for example, by using socket activation with socket
units, see systemd.socket(5)) are unaffected. Also, sockets created
with socketpair() (which creates connected AF_UNIX sockets only)
are unaffected. Note that this option has no effect on 32-bit x86,
s390, s390x, mips, mips-le, ppc, ppc-le, pcc64, 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 whitelist as it is
frequently used for local communication, including for syslog(2)
logging.
RestrictNamespaces=
Restricts access to Linux namespace functionality for the processes
of this unit. For details about Linux namespaces, see
namespaces(7). Either takes a boolean argument, or a
space-separated list of namespace type identifiers. If false (the
default), no restrictions on namespace creation and switching are
made. If true, access to any kind of namespacing is prohibited.
Otherwise, a space-separated list of namespace type identifiers
must be specified, consisting of any combination of: cgroup, ipc,
net, mnt, pid, user and uts. Any namespace type listed is made
accessible to the unit's processes, access to namespace types not
listed is prohibited (whitelisting). 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 (blacklisting). If the empty string is assigned, the
default namespace restrictions are applied, which is equivalent to
false. This option may appear more than once, in which case the
namespace types are merged by OR, or by AND if the lines are
prefixed with "~" (see examples below). Internally, this setting
limits access to the unshare(2), clone(2) and setns(2) system
calls, taking the specified flags parameters into account. Note
that -- if this option is used -- in addition to restricting
creation and switching of the specified types of namespaces (or all
of them, if true) access to the setns() system call with a zero
flags parameter is prohibited. This setting is only supported on
x86, x86-64, mips, mips-le, mips64, mips64-le, mips64-n32,
mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces no
restrictions on other architectures. 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 personality(2)
system call so that the kernel execution domain may not be changed
from the default or the personality selected with Personality=
directive. This may be useful to improve security, because odd
personality emulations may be poorly tested and source of
vulnerabilities. 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 mmap(2) system calls
with both PROT_EXEC and PROT_WRITE set, mprotect(2) or
pkey_mprotect(2) system calls with PROT_EXEC set and shmat(2)
system calls with SHM_EXEC set. Note that this option is
incompatible with programs and libraries that generate program code
dynamically at runtime, including JIT execution engines, executable
stacks, and code "trampoline" feature of various C compilers. This
option improves service security, as it makes harder for software
exploits to change running code dynamically. However, the
protection can be circumvented, if the service can write to a
filesystem, which is not mounted with noexec (such as /dev/shm), or
it can use memfd_create(). This can be prevented by making such
file systems inaccessible to the service (e.g.
InaccessiblePaths=/dev/shm) and installing further system call
filters (SystemCallFilter=~memfd_create). Note that this feature is
fully available on x86-64, and partially on x86. Specifically, the
shmat() protection is not available on x86. Note that on systems
supporting multiple ABIs (such as x86/x86-64) it is recommended to
turn off alternative ABIs for services, so that they cannot be used
to circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with
SystemCallArchitectures=native or similar. 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 sched(7) 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
inode(7)). 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.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
PrivateMounts=
Takes a boolean parameter. If set, the processes of this unit will
be run in their own private file system (mount) namespace with all
mount propagation from the processes towards the host's main file
system namespace turned off. This means any file system mount
points established or removed by the unit's processes will be
private to them and not be visible to the host. However, file
system mount points established or removed on the host will be
propagated to the unit's processes. See mount_namespaces(7) for
details on file system namespaces. Defaults to off.
When turned on, this executes three operations for each invoked
process: a new CLONE_NEWNS namespace is created, after which all
existing mounts are remounted to MS_SLAVE to disable propagation
from the unit's processes to the host (but leaving propagation in
the opposite direction in effect). Finally, the mounts are
remounted again to the propagation mode configured with
MountFlags=, see below.
File system namespaces are set up individually for each process
forked off by the service manager. Mounts established in the
namespace of the process created by ExecStartPre= will hence be
cleaned up automatically as soon as that process exits and will not
be available to subsequent processes forked off for ExecStart= (and
similar applies to the various other commands configured for
units). Similarly, JoinsNamespaceOf= does not permit sharing kernel
mount namespaces between units, it only enables sharing of the
/tmp/ and /var/tmp/ directories.
Other file system namespace unit settings -- PrivateMounts=,
PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=, ... -- also
enable file system namespacing in a fashion equivalent to this
option. Hence it is primarily useful to explicitly request this
behaviour if none of the other settings are used.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
MountFlags=
Takes a mount propagation setting: shared, slave or private, which
controls whether file system mount points in the file system
namespaces set up for this unit's processes will receive or
propagate mounts and unmounts from other file system namespaces.
See mount(2) for details on mount propagation, and the three
propagation flags in particular.
This setting only controls the final propagation setting in effect
on all mount points of the file system namespace created for each
process of this unit. Other file system namespacing unit settings
(see the discussion in PrivateMounts= above) will implicitly
disable mount and unmount propagation from the unit's processes
towards the host by changing the propagation setting of all mount
points in the unit's file system namepace to slave first. Setting
this option to shared does not reestablish propagation in that
case.
If not set - but file system namespaces are enabled through another
file system namespace unit setting - shared mount propagation is
used, but -- as mentioned -- as slave is applied first, propagation
from the unit's processes to the host is still turned off.
It is not recommended to to use private mount propagation for
units, as this means temporary mounts (such as removable media) of
the host will stay mounted and thus indefinitely busy in forked off
processes, as unmount propagation events won't be received by the
file system namespace of the unit.
Usually, it is best to leave this setting unmodified, and use
higher level file system namespacing options instead, in particular
PrivateMounts=, see above.
This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.
SYSTEM CALL FILTERING
SystemCallFilter=
Takes a space-separated list of system call names. If this setting
is used, all system calls executed by the unit processes except for
the listed ones will result in immediate process termination with
the SIGSYS signal (whitelisting). (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 (blacklisting).
Blacklisted system calls and system call groups may optionally be
suffixed with a colon (":") and "errno" error number (between 0 and
4095) or errno name such as EPERM, EACCES or EUCLEAN (see errno(3)
for a full list). This value will be returned when a blacklisted
system call is triggered, instead of terminating the processes
immediately. 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 whitelisted and
do not need to be listed explicitly. This option may be specified
more than once, in which case the filter masks are merged. If the
empty string is assigned, the filter is reset, all prior
assignments will have no effect. 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. whitelisting and
blacklisting), the first encountered will take precedence and will
dictate the default action (termination or approval of a system
call). Then the next occurrences of this option will add or delete
the listed system calls from the set of the filtered system calls,
depending of its type and the default action. (For example, if you
have started with a whitelisting of read and write, and right after
it add a blacklisting of write, then write will be removed from the
set.)
As the number of possible system calls is large, predefined sets of
system calls are provided. A set starts with "@" character,
followed by name of the set.
Table 3. Currently predefined system call sets
+----------------+----------------------------+
|Set | Description |
+----------------+----------------------------+
|@aio | Asynchronous I/O |
| | (io_setup(2), |
| | io_submit(2), and related |
| | calls) |
+----------------+----------------------------+
|@basic-io | System calls for basic |
| | I/O: reading, writing, |
| | seeking, file descriptor |
| | duplication and closing |
| | (read(2), write(2), and |
| | related calls) |
+----------------+----------------------------+
|@chown | Changing file ownership |
| | (chown(2), fchownat(2), |
| | and related calls) |
+----------------+----------------------------+
|@clock | System calls for changing |
| | the system clock |
| | (adjtimex(2), |
| | settimeofday(2), and |
| | related calls) |
+----------------+----------------------------+
|@cpu-emulation | System calls for CPU |
| | emulation functionality |
| | (vm86(2) and related |
| | calls) |
+----------------+----------------------------+
|@debug | Debugging, performance |
| | monitoring and tracing |
| | functionality (ptrace(2), |
| | perf_event_open(2) and |
| | related calls) |
+----------------+----------------------------+
|@file-system | File system operations: |
| | opening, creating files |
| | and directories for read |
| | and write, renaming and |
| | removing them, reading |
| | file properties, or |
| | creating hard and symbolic |
| | links. |
+----------------+----------------------------+
|@io-event | Event loop system calls |
| | (poll(2), select(2), |
| | epoll(7), eventfd(2) and |
| | related calls) |
+----------------+----------------------------+
|@ipc | Pipes, SysV IPC, POSIX |
| | Message Queues and other |
| | IPC (mq_overview(7), |
| | svipc(7)) |
+----------------+----------------------------+
|@keyring | Kernel keyring access |
| | (keyctl(2) and related |
| | calls) |
+----------------+----------------------------+
|@memlock | Locking of memory into RAM |
| | (mlock(2), mlockall(2) and |
| | related calls) |
+----------------+----------------------------+
|@module | Loading and unloading of |
| | kernel modules |
| | (init_module(2), |
| | delete_module(2) and |
| | related calls) |
+----------------+----------------------------+
|@mount | Mounting and unmounting of |
| | file systems (mount(2), |
| | chroot(2), and related |
| | calls) |
+----------------+----------------------------+
|@network-io | Socket I/O (including |
| | local AF_UNIX): socket(7), |
| | unix(7) |
+----------------+----------------------------+
|@obsolete | Unusual, obsolete or |
| | unimplemented |
| | (create_module(2), |
| | gtty(2), ...) |
+----------------+----------------------------+
|@privileged | All system calls which |
| | need super-user |
| | capabilities |
| | (capabilities(7)) |
+----------------+----------------------------+
|@process | Process control, |
| | execution, namespaceing |
| | operations (clone(2), |
| | kill(2), namespaces(7), |
| | ... |
+----------------+----------------------------+
|@raw-io | Raw I/O port access |
| | (ioperm(2), iopl(2), |
| | pciconfig_read(), ...) |
+----------------+----------------------------+
|@reboot | System calls for rebooting |
| | and reboot preparation |
| | (reboot(2), kexec(), ...) |
+----------------+----------------------------+
|@resources | System calls for changing |
| | resource limits, memory |
| | and scheduling parameters |
| | (setrlimit(2), |
| | setpriority(2), ...) |
+----------------+----------------------------+
|@setuid | System calls for changing |
| | user ID and group ID |
| | credentials, (setuid(2), |
| | setgid(2), setresuid(2), |
| | ...) |
+----------------+----------------------------+
|@signal | System calls for |
| | manipulating and handling |
| | process signals |
| | (signal(2), |
| | sigprocmask(2), ...) |
+----------------+----------------------------+
|@swap | System calls for |
| | enabling/disabling swap |
| | devices (swapon(2), |
| | swapoff(2)) |
+----------------+----------------------------+
|@sync | Synchronizing files and |
| | memory to disk: (fsync(2), |
| | msync(2), and related |
| | calls) |
+----------------+----------------------------+
|@system-service | A reasonable set of system |
| | calls used by common |
| | system services, excluding |
| | any special purpose calls. |
| | This is the recommended |
| | starting point for |
| | whitelisting system calls |
| | for system services, as it |
| | contains what is typically |
| | needed by system services, |
| | but excludes overly |
| | specific interfaces. For |
| | example, the following |
| | APIs are excluded: |
| | "@clock", "@mount", |
| | "@swap", "@reboot". |
+----------------+----------------------------+
|@timer | System calls for |
| | scheduling operations by |
| | time (alarm(2), |
| | timer_create(2), ...) |
+----------------+----------------------------+
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, whitelisting system calls (rather than blacklisting) is
the safer mode of operation. It is recommended to enforce system
call whitelists for all long-running system services. Specifically,
the following lines are a relatively safe basic choice for the
majority of system services:
[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERM
Note that various kernel system calls are defined redundantly:
there are multiple system calls for executing the same operation.
For example, the pidfd_send_signal() system call may be used to
execute operations similar to what can be done with the older
kill() system call, hence blocking the latter without the former
only provides weak protection. Since new system calls are added
regularly to the kernel as development progresses, keeping system
call blacklists comprehensive requires constant work. It is thus
recommended to use whitelisting instead, which offers the benefit
that new system calls are by default implicitly blocked until the
whitelist 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 errno(3) for a full list
of error codes. When this setting is not used, or when the empty
string 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.unit(5), as well as x32, mips64-n32, mips64-le-n32, and the
special identifier native. The special identifier native implicitly
maps to the native architecture of the system (or more precisely:
to the architecture the system manager is compiled for). 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
system call architecture filtering is applied.
If this setting is used, processes of this unit will only be
permitted to call native system calls, and system calls of the
specified architectures. For the purposes of this option, the x32
architecture is treated as including x86-64 system calls. However,
this setting still fulfills its purpose, as explained below, on
x32.
System call filtering is not equally effective on all
architectures. For example, on x86 filtering of network
socket-related calls is not possible, due to ABI limitations -- a
limitation that x86-64 does not have, however. On systems
supporting multiple ABIs at the same time -- such as x86/x86-64 --
it is hence recommended to limit the set of permitted system call
architectures so that secondary ABIs may not be used to circumvent
the restrictions applied to the native ABI of the system. In
particular, setting SystemCallArchitectures=native is a good choice
for disabling non-native ABIs.
System call architectures may also be restricted system-wide via
the SystemCallArchitectures= option in the global configuration.
See systemd-system.conf(5) for details.
ENVIRONMENT
Environment=
Sets environment variables for executed processes. Takes a
space-separated list of variable assignments. This option may be
specified more than once, in which case all listed variables will
be set. If the same variable is set twice, the later setting will
override the earlier setting. If the empty string is assigned to
this option, the list of environment variables is reset, all prior
assignments have no effect. Variable expansion is not performed
inside the strings, 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.
Example:
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
gives three variables "VAR1", "VAR2", "VAR3" with the values "word1
word2", "word3", "$word 5 6".
See environ(7) for details about environment variables.
Note that environment variables are not suitable for passing
secrets (such as passwords, key material, ...) to service
processes. Environment variables set for a unit are exposed to
unprivileged clients via D-Bus IPC, and generally not understood as
being data that requires protection. Moreover, environment
variables are propagated down the process tree, including across
security boundaries (such as setuid/setgid executables), and hence
might leak to processes that should not have access to the secret
data.
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[5] are supported, but not most control characters[6].
"\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[5] are supported, but not most control characters[6].
"\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 environ(7) 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 environ(7) for details about environment variables.
LOGGING AND STANDARD INPUT/OUTPUT
StandardInput=
Controls where file descriptor 0 (STDIN) of the executed processes
is connected to. Takes one of null, tty, tty-force, tty-fail, data,
file:path, socket or fd:name.
If null is selected, standard input will be connected to /dev/null,
i.e. all read attempts by the process will result in immediate EOF.
If tty is selected, standard input is connected to a TTY (as
configured by TTYPath=, see below) and the executed process becomes
the controlling process of the terminal. If the terminal is already
being controlled by another process, the executed process waits
until the current controlling process releases the terminal.
tty-force is similar to tty, but the executed process is forcefully
and immediately made the controlling process of the terminal,
potentially removing previous controlling processes from the
terminal.
tty-fail is similar to tty, but if the terminal already has a
controlling process start-up of the executed process fails.
The data option may be used to configure arbitrary textual or
binary data to pass via standard input to the executed process. The
data to pass is configured via
StandardInputText=/StandardInputData= (see below). Note that the
actual file descriptor type passed (memory file, regular file, UNIX
pipe, ...) might depend on the kernel and available privileges. In
any case, the file descriptor is read-only, and when read returns
the specified data followed by EOF.
The file:path option may be used to connect a specific file system
object to standard input. An absolute path following the ":"
character is expected, which may refer to a regular file, a FIFO or
special file. If an AF_UNIX socket in the file system is specified,
a stream socket is connected to it. The latter is useful for
connecting standard input of processes to arbitrary system
services.
The socket option is valid in socket-activated services only, and
requires the relevant socket unit file (see systemd.socket(5) for
details) to have Accept=yes set, or to specify a single socket
only. If this option is set, standard input will be connected to
the socket the service was activated from, which is primarily
useful for compatibility with daemons designed for use with the
traditional inetd(8) socket activation daemon.
The fd:name option connects standard input to a specific, named
file descriptor provided by a socket unit. The name may be
specified as part of this option, following a ":" character (e.g.
"fd:foobar"). If no name is specified, the name "stdin" is implied
(i.e. "fd" is equivalent to "fd:stdin"). At least one socket unit
defining the specified name must be provided via the Sockets=
option, and the file descriptor name may differ from the name of
its containing socket unit. If multiple matches are found, the
first one will be used. See FileDescriptorName= in
systemd.socket(5) for more details about named file descriptors and
their ordering.
This setting defaults to null.
Note that services which specify DefaultDependencies=no and use
StandardInput= or StandardOutput= with tty/tty-force/tty-fail,
should specify After=systemd-vconsole-setup.service, to make sure
that the tty initialization is finished before they start.
StandardOutput=
Controls where file descriptor 1 (stdout) of the executed processes
is connected to. Takes one of inherit, null, tty, journal, kmsg,
journal+console, kmsg+console, file:path, append:path, socket or
fd:name.
inherit duplicates the file descriptor of standard input for
standard output.
null connects standard output to /dev/null, i.e. everything written
to it will be lost.
tty connects standard output to a tty (as configured via TTYPath=,
see below). If the TTY is used for output only, the executed
process will not become the controlling process of the terminal,
and will not fail or wait for other processes to release the
terminal.
journal connects standard output with the journal, which is
accessible via journalctl(1). Note that everything that is written
to kmsg (see below) is implicitly stored in the journal as well,
the specific option listed below is hence a superset of this one.
(Also note that any external, additional syslog daemons receive
their log data from the journal, too, hence this is the option to
use when logging shall be processed with such a daemon.)
kmsg connects standard output with the kernel log buffer which is
accessible via dmesg(1), in addition to the journal. The journal
daemon might be configured to send all logs to kmsg anyway, in
which case this option is no different from journal.
journal+console and kmsg+console work in a similar way as the two
options above but copy the output to the system console as well.
The file:path option may be used to connect a specific file system
object to standard output. The semantics are similar to the same
option of StandardInput=, see above. If path refers to a regular
file on the filesystem, it is opened (created if it doesn't exist
yet) for writing at the beginning of the file, but without
truncating it. If standard input and output are directed to the
same file path, it is opened only once, for reading as well as
writing and duplicated. This is particularly useful when the
specified path refers to an AF_UNIX socket in the file system, as
in that case only a single stream connection is created for both
input and output.
append:path is similar to file:path above, but it opens the file in
append mode.
socket connects standard output to a socket acquired via socket
activation. The semantics are similar to the same option of
StandardInput=, see above.
The fd:name option connects standard output to a specific, named
file descriptor provided by a socket unit. A name may be specified
as part of this option, following a ":" character (e.g.
"fd:foobar"). If no name is specified, the name "stdout" is implied
(i.e. "fd" is equivalent to "fd:stdout"). At least one socket unit
defining the specified name must be provided via the Sockets=
option, and the file descriptor name may differ from the name of
its containing socket unit. If multiple matches are found, the
first one will be used. See FileDescriptorName= in
systemd.socket(5) for more details about named descriptors and
their ordering.
If the standard output (or error output, see below) of a unit is
connected to the journal or the kernel log buffer, the unit will
implicitly gain a dependency of type After= on
systemd-journald.socket (also see the "Implicit Dependencies"
section above). Also note that in this case stdout (or stderr, see
below) will be an AF_UNIX stream socket, and not a pipe or FIFO
that can be re-opened. This means when executing shell scripts the
construct echo "hello" > /dev/stderr for writing text to stderr
will not work. To mitigate this use the construct echo "hello" >&2
instead, which is mostly equivalent and avoids this pitfall.
This setting defaults to the value set with DefaultStandardOutput=
in systemd-system.conf(5), which defaults to journal. Note that
setting this parameter might result in additional dependencies to
be added to the unit (see above).
StandardError=
Controls where file descriptor 2 (stderr) of the executed processes
is connected to. The available options are identical to those of
StandardOutput=, with some exceptions: if set to inherit the file
descriptor used for standard output is duplicated for standard
error, while fd:name will use a default file descriptor name of
"stderr".
This setting defaults to the value set with DefaultStandardError=
in systemd-system.conf(5), which defaults to inherit. Note that
setting this parameter might result in additional dependencies to
be added to the unit (see above).
StandardInputText=, StandardInputData=
Configures arbitrary textual or binary data to pass via file
descriptor 0 (STDIN) to the executed processes. These settings have
no effect unless StandardInput= is set to data. 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[7]. No escape sequences or specifiers are resolved. Any
whitespace in the encoded version is ignored during decoding.
Note that StandardInputText= and StandardInputData= operate on the
same data buffer, and may be mixed in order to configure both
binary and textual data for the same input stream. The textual or
binary data is joined strictly in the order the settings appear in
the unit file. Assigning an empty string to either will reset the
data buffer.
Please keep in mind that in order to maintain readability long unit
file settings may be split into multiple lines, by suffixing each
line (except for the last) with a "\" character (see
systemd.unit(5) for details). This is particularly useful for large
data configured with these two options. Example:
...
StandardInput=data
StandardInputData=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 emerg (lowest log level,
only highest priority messages), alert, crit, err, warning, notice,
info, debug (highest log level, also lowest priority messages). See
syslog(3) for details. By default no filtering is applied (i.e. the
default maximum log level is debug). Use this option to configure
the logging system to drop log messages of a specific service above
the specified level. For example, set LogLevelMax=info in order to
turn off debug logging of a particularly chatty unit. Note that the
configured level is applied to any log messages written by any of
the processes belonging to this unit, sent via any supported
logging protocol. The filtering is applied early in the logging
pipeline, before any kind of further processing is done. Moreover,
messages which pass through this filter successfully might still be
dropped by filters applied at a later stage in the logging
subsystem. For example, MaxLevelStore= configured in
journald.conf(5) might prohibit messages of higher log levels to be
stored on disk, even though the per-unit LogLevelMax= permitted it
to be processed.
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-
fields(7) for details on the journal field concept. Even though the
underlying journal implementation permits binary field values, this
setting accepts only valid UTF-8 values. To include space
characters in a journal field value, enclose the assignment in
double quotes ("). The usual specifiers are expanded in all
assignments (see below). Note that this setting is not only useful
for attaching additional metadata to log records of a unit, but
given that all fields and values are indexed may also be used to
implement cross-unit log record matching. Assign an empty string to
reset the list.
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.time(7)
for details). The default settings are set by RateLimitIntervalSec=
and RateLimitBurst= configured in journald.conf(5).
LogNamespace=
Run the unit's processes in the specified journal namespace.
Expects a short user-defined string identifying the namespace. If
not used the processes of the service are run in the default
journal namespace, i.e. their log stream is collected and processed
by systemd-journald.service. If this option is used any log data
generated by processes of this unit (regardless if via the
syslog(), journal native logging or stdout/stderr logging) is
collected and processed by an instance of the
systemd-journald@.service template unit, which manages the
specified namespace. The log data is stored in a data store
independent from the default log namespace's data store. See
systemd-journald.service(8) for details about journal namespaces.
Internally, journal namespaces are implemented through Linux mount
namespacing and over-mounting the directory that contains the
relevant AF_UNIX sockets used for logging in the unit's mount
namespace. Since mount namespaces are used this setting disconnects
propagation of mounts from the unit's processes to the host,
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 journalctl(1) output, unless the --namespace= 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
journal or kmsg (or to the same settings in combination with
+console) and only applies to log messages written to stdout or
stderr.
SyslogFacility=
Sets the syslog facility identifier to use when logging. One of
kern, user, mail, daemon, auth, syslog, lpr, news, uucp, cron,
authpriv, ftp, local0, local1, local2, local3, local4, local5,
local6 or local7. See syslog(3) for details. This option is only
useful when StandardOutput= or StandardError= are set to journal or
kmsg (or to the same settings in combination with +console), and
only applies to log messages written to stdout or stderr. Defaults
to daemon.
SyslogLevel=
The default syslog log level to use when logging to the logging
system or the kernel log buffer. One of emerg, alert, crit, err,
warning, notice, info, debug. See syslog(3) for details. This
option is only useful when StandardOutput= or StandardError= are
set to journal or kmsg (or to the same settings in combination with
+console), and only applies to log messages written to stdout or
stderr. Note that individual lines output by executed processes may
be prefixed with a different log level which can be used to
override the default log level specified here. The interpretation
of these prefixes may be disabled with SyslogLevelPrefix=, see
below. For details, see sd-daemon(3). Defaults to info.
SyslogLevelPrefix=
Takes a boolean argument. If true and StandardOutput= or
StandardError= are set to journal or kmsg (or to the same settings
in combination with +console), log lines written by the executed
process that are prefixed with a log level will be processed with
this log level set but the prefix removed. If set to false, the
interpretation of these prefixes is disabled and the logged lines
are passed on as-is. This only applies to log messages written to
stdout or stderr. For details about this prefixing see sd-
daemon(3). Defaults to true.
TTYPath=
Sets the terminal device node to use if standard input, output, or
error are connected to a TTY (see above). Defaults to /dev/console.
TTYReset=
Reset the terminal device specified with TTYPath= before and after
execution. Defaults to "no".
TTYVHangup=
Disconnect all clients which have opened the terminal device
specified with TTYPath= before and after execution. Defaults to
"no".
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".
SYSTEM V COMPATIBILITY
UtmpIdentifier=
Takes a four character identifier string for an utmp(5) and wtmp
entry for this service. This should only be set for services such
as getty implementations (such as agetty(8)) where utmp/wtmp
entries must be created and cleared before and after execution, or
for services that shall be executed as if they were run by a getty
process (see below). If the configured string is longer than four
characters, it is truncated and the terminal four characters are
used. This setting interprets %I style string replacements. This
setting is unset by default, i.e. no utmp/wtmp entries are created
or cleaned up for this service.
UtmpMode=
Takes one of "init", "login" or "user". If UtmpIdentifier= is set,
controls which type of utmp(5)/wtmp entries for this service are
generated. This setting has no effect unless UtmpIdentifier= is set
too. If "init" is set, only an INIT_PROCESS entry is generated and
the invoked process must implement a getty-compatible utmp/wtmp
logic. If "login" is set, first an INIT_PROCESS entry, followed by
a LOGIN_PROCESS entry is generated. In this case, the invoked
process must implement a login(1)-compatible utmp/wtmp logic. If
"user" is set, first an INIT_PROCESS entry, then a LOGIN_PROCESS
entry and finally a USER_PROCESS entry is generated. In this case,
the invoked process may be any process that is suitable to be run
as session leader. Defaults to "init".
ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
Processes started by the service manager are executed with an
environment variable block assembled from multiple sources. Processes
started by the system service manager generally do not inherit
environment variables set for the service manager itself (but this may
be altered via PassEnvironment=), but processes started by the user
service manager instances generally do inherit all environment
variables set for the service manager itself.
For each invoked process the list of environment variables set is
compiled from the following sources:
o Variables globally configured for the service manager, using the
DefaultEnvironment= setting in systemd-system.conf(5), the kernel
command line option systemd.setenv= (see systemd(1)) or via
systemctl set-environment (see systemctl(1)).
o Variables defined by the service manager itself (see the list
below)
o Variables set in the service manager's own environment variable
block (subject to PassEnvironment= for the system service manager)
o Variables set via Environment= in the unit file
o Variables read from files specified via EnvironmentFile= in the
unit file
o Variables set by any PAM modules in case PAMName= is in effect,
cf. pam_env(8)
If 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 select environment variables are set or propagated by the
service manager for each invoked process:
$PATH
Colon-separated list of directories to use when launching
executables. systemd uses a fixed value of
"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system
manager. 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.
$LANG
Locale. Can be set in locale.conf(5) or on the kernel command line
(see systemd(1) and kernel-command-line(7)).
$USER, $LOGNAME, $HOME, $SHELL
User 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 passwd(5).
$INVOCATION_ID
Contains 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_DIR
The directory to use for runtime objects (such as IPC objects) and
volatile state. Set for all services run by the user systemd
instance, as well as any system services that use PAMName= with a
PAM stack that includes pam_systemd. See below and pam_systemd(8)
for more information.
$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY,
$LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY
Contains and absolute paths to the directories defined with
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, and ConfigurationDirectory= when those settings are
used.
$MAINPID
The PID of the unit's main process if it is known. This is only set
for control processes as invoked by ExecReload= and similar.
$MANAGERPID
The PID of the user systemd instance, set for processes spawned by
it.
$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a service for socket
activation. See sd_listen_fds(3).
$NOTIFY_SOCKET
The socket sd_notify() talks to. See sd_notify(3).
$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive notifications. See
sd_watchdog_enabled(3).
$TERM
Terminal type, set only for units connected to a terminal
(StandardInput=tty, StandardOutput=tty, or StandardError=tty). See
termcap(5).
$JOURNAL_STREAM
If the standard output or standard error output of the executed
processes are connected to the journal (for example, by setting
StandardError=journal) $JOURNAL_STREAM contains the device and
inode numbers of the connection file descriptor, formatted in
decimal, separated by a colon (":"). This permits invoked processes
to safely detect whether their standard output or standard error
output are connected to the journal. The device and inode numbers
of the file descriptors should be compared with the values set in
the environment variable to determine whether the process output is
still connected to the journal. Note that it is generally not
sufficient to only check whether $JOURNAL_STREAM is set at all as
services might invoke external processes replacing their standard
output or standard error output, without unsetting the environment
variable.
If both standard output and standard error of the executed
processes are connected to the journal via a stream socket, this
environment variable will contain information about the standard
error stream, as that's usually the preferred destination for log
data. (Note that typically the same stream is used for both
standard output and standard error, hence very likely the
environment variable contains device and inode information matching
both stream file descriptors.)
This environment variable is primarily useful to allow services to
optionally upgrade their used log protocol to the native journal
protocol (using sd_journal_print(3) and other functions) if their
standard output or standard error output is connected to the
journal anyway, thus enabling delivery of structured metadata along
with logged messages.
$SERVICE_RESULT
Only 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:
Table 4. Defined $SERVICE_RESULT values
+------------------+----------------------------+
|Value | Meaning |
+------------------+----------------------------+
|"success" | The service ran |
| | successfully and exited |
| | cleanly. |
+------------------+----------------------------+
|"protocol" | A protocol violation |
| | occurred: the service did |
| | not take the steps |
| | required by its unit |
| | configuration |
| | (specifically what is |
| | configured in its Type= |
| | setting). |
+------------------+----------------------------+
|"timeout" | One of the steps timed |
| | out. |
+------------------+----------------------------+
|"exit-code" | Service process exited |
| | with a non-zero exit code; |
| | see $EXIT_CODE below for |
| | the actual exit code |
| | returned. |
+------------------+----------------------------+
|"signal" | A service process was |
| | terminated abnormally by a |
| | signal, without dumping |
| | core. See $EXIT_CODE below |
| | for the actual signal |
| | causing the termination. |
+------------------+----------------------------+
|"core-dump" | A service process |
| | terminated abnormally with |
| | a signal and dumped core. |
| | See $EXIT_CODE below for |
| | the signal causing the |
| | termination. |
+------------------+----------------------------+
|"watchdog" | Watchdog keep-alive ping |
| | was enabled for the |
| | service, but the deadline |
| | was missed. |
+------------------+----------------------------+
|"start-limit-hit" | A start limit was defined |
| | for the unit and it was |
| | hit, causing the unit to |
| | fail to start. See |
| | systemd.unit(5)'s |
| | StartLimitIntervalSec= and |
| | StartLimitBurst= for |
| | details. |
+------------------+----------------------------+
|"resources" | A catch-all condition in |
| | case a system operation |
| | failed. |
+------------------+----------------------------+
This environment variable is useful to monitor failure or
successful termination of a service. Even though this variable is
available in both ExecStop= and ExecStopPost=, it is usually a
better choice to place monitoring tools in the latter, as the
former is only invoked for services that managed to start up
correctly, and the latter covers both services that failed during
their start-up and those which failed during their runtime.
$EXIT_CODE, $EXIT_STATUS
Only defined for the service unit type, these environment variables
are passed to all ExecStop=, ExecStopPost= processes and contain
exit status/code information of the main process of the service.
For the precise definition of the exit code and status, see
wait(2). $EXIT_CODE is one of "exited", "killed", "dumped".
$EXIT_STATUS contains the numeric exit code formatted as string if
$EXIT_CODE is "exited", and the signal name in all other cases.
Note that these environment variables are only set if the service
manager succeeded to start and identify the main process of the
service.
Table 5. Summary of possible service result variable values
+------------------+------------------+---------------------+
|$SERVICE_RESULT | $EXIT_CODE | $EXIT_STATUS |
+------------------+------------------+---------------------+
|"success" | "killed" | "HUP", "INT", |
| | | "TERM", "PIPE" |
| +------------------+---------------------+
| | "exited" | "0" |
+------------------+------------------+---------------------+
|"protocol" | not set | not set |
| +------------------+---------------------+
| | "exited" | "0" |
+------------------+------------------+---------------------+
|"timeout" | "killed" | "TERM", "KILL" |
| +------------------+---------------------+
| | "exited" | "0", "1", "2", "3", |
| | | ..., "255" |
+------------------+------------------+---------------------+
|"exit-code" | "exited" | "1", "2", "3", ..., |
| | | "255" |
+------------------+------------------+---------------------+
|"signal" | "killed" | "HUP", "INT", |
| | | "KILL", ... |
+------------------+------------------+---------------------+
|"core-dump" | "dumped" | "ABRT", "SEGV", |
| | | "QUIT", ... |
+------------------+------------------+---------------------+
|"watchdog" | "dumped" | "ABRT" |
| +------------------+---------------------+
| | "killed" | "TERM", "KILL" |
| +------------------+---------------------+
| | "exited" | "0", "1", "2", "3", |
| | | ..., "255" |
+------------------+------------------+---------------------+
|"exec-condition" | "exited" | "1", "2", "3", "4", |
| | | ..., "254" |
+------------------+------------------+---------------------+
|"oom-kill" | "killed" | "TERM", "KILL" |
+------------------+------------------+---------------------+
|"start-limit-hit" | not set | not set |
+------------------+------------------+---------------------+
|"resources" | any of the above | any of the above |
+------------------+------------------+---------------------+
|Note: the process may be also terminated by a signal not |
|sent by systemd. In particular the process may send an |
|arbitrary signal to itself in a handler for any of the |
|non-maskable signals. Nevertheless, in the "timeout" and |
|"watchdog" rows above only the signals that systemd sends |
|have been included. Moreover, using SuccessExitStatus= |
|additional exit statuses may be declared to indicate clean |
|termination, which is not reflected by this table. |
+-----------------------------------------------------------+
$PIDFILE
The path to the configured PID file, in case the process is forked
off on behalf of a service that uses the PIDFile= setting, see
systemd.service(5) for details. Service code may use this
environment variable to automatically generate a PID file at the
location configured in the unit file. This field is set to an
absolute path in the file system.
For system services, when PAMName= is enabled and pam_systemd is part
of the selected PAM stack, additional environment variables defined by
systemd may be set for services. Specifically, these are $XDG_SEAT,
$XDG_VTNR, see pam_systemd(8) for details.
PROCESS EXIT CODES
When invoking a unit process the service manager possibly fails to
apply the execution parameters configured with the settings above. In
that case the already created service process will exit with a non-zero
exit code before the configured command line is executed. (Or in other
words, the child process possibly exits with these error codes, after
having been created by the fork(2) system call, but before the matching
execve(2) system call is called.) Specifically, exit codes defined by
the C library, by the LSB specification and by the systemd service
manager itself are used.
The following basic service exit codes are defined by the C library.
Table 6. Basic C library exit codes
+----------+---------------+--------------------+
|Exit Code | Symbolic Name | Description |
+----------+---------------+--------------------+
|0 | EXIT_SUCCESS | Generic success |
| | | code. |
+----------+---------------+--------------------+
|1 | EXIT_FAILURE | Generic failure or |
| | | unspecified error. |
+----------+---------------+--------------------+
The following service exit codes are defined by the LSB
specification[8].
Table 7. LSB service exit codes
+----------+----------------------+--------------------+
|Exit Code | Symbolic Name | Description |
+----------+----------------------+--------------------+
|2 | EXIT_INVALIDARGUMENT | Invalid or excess |
| | | arguments. |
+----------+----------------------+--------------------+
|3 | EXIT_NOTIMPLEMENTED | Unimplemented |
| | | feature. |
+----------+----------------------+--------------------+
|4 | EXIT_NOPERMISSION | The user has |
| | | insufficient |
| | | privileges. |
+----------+----------------------+--------------------+
|5 | EXIT_NOTINSTALLED | The program is not |
| | | installed. |
+----------+----------------------+--------------------+
|6 | EXIT_NOTCONFIGURED | The program is not |
| | | configured. |
+----------+----------------------+--------------------+
|7 | EXIT_NOTRUNNING | The program is not |
| | | running. |
+----------+----------------------+--------------------+
The LSB specification suggests that error codes 200 and above are
reserved for implementations. Some of them are used by the service
manager to indicate problems during process invocation:
Table 8. systemd-specific exit codes
+----------+------------------------------+---------------------------------------------+
|Exit Code | Symbolic Name | Description |
+----------+------------------------------+---------------------------------------------+
|200 | EXIT_CHDIR | Changing to the |
| | | requested working |
| | | directory failed. |
| | | See |
| | | WorkingDirectory= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|201 | EXIT_NICE | Failed to set up |
| | | process scheduling |
| | | priority (nice |
| | | level). See Nice= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|202 | EXIT_FDS | Failed to close |
| | | unwanted file |
| | | descriptors, or to |
| | | adjust passed file |
| | | descriptors. |
+----------+------------------------------+---------------------------------------------+
|203 | EXIT_EXEC | The actual process |
| | | execution failed |
| | | (specifically, the |
| | | execve(2) system |
| | | call). Most likely |
| | | this is caused by a |
| | | missing or |
| | | non-accessible |
| | | executable file. |
+----------+------------------------------+---------------------------------------------+
|204 | EXIT_MEMORY | Failed to perform |
| | | an action due to |
| | | memory shortage. |
+----------+------------------------------+---------------------------------------------+
|205 | EXIT_LIMITS | Failed to adjust |
| | | resource limits. |
| | | See LimitCPU= and |
| | | related settings |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|206 | EXIT_OOM_ADJUST | Failed to adjust |
| | | the OOM setting. |
| | | See OOMScoreAdjust= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|207 | EXIT_SIGNAL_MASK | Failed to set |
| | | process signal |
| | | mask. |
+----------+------------------------------+---------------------------------------------+
|208 | EXIT_STDIN | Failed to set up |
| | | standard input. See |
| | | StandardInput= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|209 | EXIT_STDOUT | Failed to set up |
| | | standard output. |
| | | See StandardOutput= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|210 | EXIT_CHROOT | Failed to change |
| | | root directory |
| | | (chroot(2)). See |
| | | RootDirectory=/RootImage= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|211 | EXIT_IOPRIO | Failed to set up IO |
| | | scheduling priority. See |
| | | IOSchedulingClass=/IOSchedulingPriority= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|212 | EXIT_TIMERSLACK | Failed to set up timer slack. See |
| | | TimerSlackNSec= above. |
+----------+------------------------------+---------------------------------------------+
|213 | EXIT_SECUREBITS | Failed to set process secure bits. See |
| | | SecureBits= above. |
+----------+------------------------------+---------------------------------------------+
|214 | EXIT_SETSCHEDULER | Failed to set up CPU scheduling. See |
| | | CPUSchedulingPolicy=/CPUSchedulingPriority= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|215 | EXIT_CPUAFFINITY | Failed to set up CPU affinity. See |
| | | CPUAffinity= above. |
+----------+------------------------------+---------------------------------------------+
|216 | EXIT_GROUP | Failed to determine or change group |
| | | credentials. See |
| | | Group=/SupplementaryGroups= above. |
+----------+------------------------------+---------------------------------------------+
|217 | EXIT_USER | Failed to determine or change user |
| | | credentials, or to set up user namespacing. |
| | | See User=/PrivateUsers= above. |
+----------+------------------------------+---------------------------------------------+
|218 | EXIT_CAPABILITIES | Failed to drop capabilities, or apply |
| | | ambient capabilities. See |
| | | CapabilityBoundingSet=/AmbientCapabilities= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|219 | EXIT_CGROUP | Setting up the service control group |
| | | failed. |
+----------+------------------------------+---------------------------------------------+
|220 | EXIT_SETSID | Failed to create new process session. |
+----------+------------------------------+---------------------------------------------+
|221 | EXIT_CONFIRM | Execution has been cancelled by the user. |
| | | See the systemd.confirm_spawn= kernel |
| | | command line setting on kernel-command- |
| | | line(7) for details. |
+----------+------------------------------+---------------------------------------------+
|222 | EXIT_STDERR | Failed to set up standard error output. See |
| | | StandardError= above. |
+----------+------------------------------+---------------------------------------------+
|224 | EXIT_PAM | Failed to set up PAM session. See PAMName= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|225 | EXIT_NETWORK | Failed to set up network namespacing. See |
| | | PrivateNetwork= above. |
+----------+------------------------------+---------------------------------------------+
|226 | EXIT_NAMESPACE | Failed to set up mount namespacing. See |
| | | ReadOnlyPaths= and related settings above. |
+----------+------------------------------+---------------------------------------------+
|227 | EXIT_NO_NEW_PRIVILEGES | Failed to disable new privileges. See |
| | | NoNewPrivileges=yes above. |
+----------+------------------------------+---------------------------------------------+
|228 | EXIT_SECCOMP | Failed to apply system call filters. See |
| | | SystemCallFilter= and related settings |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|229 | EXIT_SELINUX_CONTEXT | Determining or changing SELinux context |
| | | failed. See SELinuxContext= above. |
+----------+------------------------------+---------------------------------------------+
|230 | EXIT_PERSONALITY | Failed to set up an execution domain |
| | | (personality). See Personality= above. |
+----------+------------------------------+---------------------------------------------+
|231 | EXIT_APPARMOR_PROFILE | Failed to prepare changing AppArmor |
| | | profile. See AppArmorProfile= above. |
+----------+------------------------------+---------------------------------------------+
|232 | EXIT_ADDRESS_FAMILIES | Failed to restrict address families. See |
| | | RestrictAddressFamilies= above. |
+----------+------------------------------+---------------------------------------------+
|233 | EXIT_RUNTIME_DIRECTORY | Setting up runtime directory failed. See |
| | | RuntimeDirectory= and related settings |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|235 | EXIT_CHOWN | Failed to adjust socket ownership. Used for |
| | | socket units only. |
+----------+------------------------------+---------------------------------------------+
|236 | EXIT_SMACK_PROCESS_LABEL | Failed to set SMACK label. See |
| | | SmackProcessLabel= above. |
+----------+------------------------------+---------------------------------------------+
|237 | EXIT_KEYRING | Failed to set up kernel keyring. |
+----------+------------------------------+---------------------------------------------+
|238 | EXIT_STATE_DIRECTORY | Failed to set up unit's state directory. |
| | | See StateDirectory= above. |
+----------+------------------------------+---------------------------------------------+
|239 | EXIT_CACHE_DIRECTORY | Failed to set up unit's cache directory. |
| | | See CacheDirectory= above. |
+----------+------------------------------+---------------------------------------------+
|240 | EXIT_LOGS_DIRECTORY | Failed to set up unit's logging directory. |
| | | See LogsDirectory= above. |
+----------+------------------------------+---------------------------------------------+
|241 | EXIT_CONFIGURATION_DIRECTORY | Failed to set up unit's configuration |
| | | directory. See ConfigurationDirectory= |
| | | above. |
+----------+------------------------------+---------------------------------------------+
|242 | EXIT_NUMA_POLICY | Failed to set up unit's NUMA memory policy. |
| | | See NUMAPolicy= and NUMAMask=above. |
+----------+------------------------------+---------------------------------------------+
Finally, the BSD operating systems define a set of exit codes,
typically defined on Linux systems too:
Table 9. BSD exit codes
+----------+----------------+---------------------+
|Exit Code | Symbolic Name | Description |
+----------+----------------+---------------------+
|64 | EX_USAGE | Command line usage |
| | | error |
+----------+----------------+---------------------+
|65 | EX_DATAERR | Data format error |
+----------+----------------+---------------------+
|66 | EX_NOINPUT | Cannot open input |
+----------+----------------+---------------------+
|67 | EX_NOUSER | Addressee unknown |
+----------+----------------+---------------------+
|68 | EX_NOHOST | Host name unknown |
+----------+----------------+---------------------+
|69 | EX_UNAVAILABLE | Service unavailable |
+----------+----------------+---------------------+
|70 | EX_SOFTWARE | internal software |
| | | error |
+----------+----------------+---------------------+
|71 | EX_OSERR | System error (e.g., |
| | | can't fork) |
+----------+----------------+---------------------+
|72 | EX_OSFILE | Critical OS file |
| | | missing |
+----------+----------------+---------------------+
|73 | EX_CANTCREAT | Can't create (user) |
| | | output file |
+----------+----------------+---------------------+
|74 | EX_IOERR | Input/output error |
+----------+----------------+---------------------+
|75 | EX_TEMPFAIL | Temporary failure; |
| | | user is invited to |
| | | retry |
+----------+----------------+---------------------+
|76 | EX_PROTOCOL | Remote error in |
| | | protocol |
+----------+----------------+---------------------+
|77 | EX_NOPERM | Permission denied |
+----------+----------------+---------------------+
|78 | EX_CONFIG | Configuration error |
+----------+----------------+---------------------+
SEE ALSO
systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-
system.conf(5), systemd.unit(5), systemd.service(5), systemd.socket(5),
systemd.swap(5), systemd.mount(5), systemd.kill(5), systemd.resource-
control(5), systemd.time(7), systemd.directives(7), tmpfiles.d(5),
exec(3)
NOTES
1. Discoverable Partitions Specification
https://systemd.io/DISCOVERABLE_PARTITIONS
2. User/Group Name Syntax
https://systemd.io/USER_NAMES
3. No New Privileges Flag
https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html
4. proc.txt
https://www.kernel.org/doc/Documentation/filesystems/proc.txt
5. C escapes
https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences
6. most control characters
https://en.wikipedia.org/wiki/Control_character#In_ASCII
7. Base64
https://tools.ietf.org/html/rfc2045#section-6.8
8. LSB specification
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
systemd 245 SYSTEMD.EXEC(5)