Provided by: systemd_237-3ubuntu10.57_amd64 
NAME
systemd.exec - Execution environment configuration
SYNOPSIS
service.service, socket.socket, mount.mount, swap.swap
DESCRIPTION
Unit configuration files for services, sockets, mount points, and swap devices share a
subset of configuration options which define the execution environment of spawned
processes.
This man page lists the configuration options shared by these four unit types. See
systemd.unit(5) for the common options of all unit configuration files, and
systemd.service(5), systemd.socket(5), systemd.swap(5), and systemd.mount(5) for more
information on the specific unit configuration files. The execution specific configuration
options are configured in the [Service], [Socket], [Mount], or [Swap] sections, depending
on the unit type.
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:
• 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=.
• 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).
• Units whose standard output or error output is connected to journal, syslog or kmsg
(or their combinations with console output, see below) automatically acquire
dependencies of type After= on systemd-journald.socket.
PATHS
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.
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].
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=.
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.
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.
CREDENTIALS
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 restrictions on the user/group name syntax are enforced: the specified name
must 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 or "_" (i.e. numbers and "-" are not permitted
as first character). The user/group name must have at least one character, and at most
31. These restrictions are enforced in order to avoid ambiguities and to ensure
user/group names and unit files remain portable among Linux systems.
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.
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=, PrivateTmp= are implied. 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 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). 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
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 AND,
or by OR 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=, 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[2].
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
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, MemoryLimit=
is a more powerful (and working) replacement for LimitRSS=.
For system units these resource limits may be chosen freely. For user units however
(i.e. units run by a per-user instance of systemd(1)), these limits are bound by
(possibly more restrictive) per-user limits enforced by the OS.
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 above).
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 the system service manager and to inherit for the user service
manager.
OOMScoreAdjust=
Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes
an integer between -1000 (to disable OOM killing for this process) and 1000 (to make
killing of this process under memory pressure very likely). See proc.txt[3] 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. 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.
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. 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). See ioprio_set(2) for details.
SANDBOXING
ProtectSystem=
Takes a boolean argument or the special values "full" or "strict". If true, mounts the
/usr and /boot directories 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. For this setting the same
restrictions regarding mount propagation and privileges apply as for ReadOnlyPaths=
and related calls, see below. Defaults to off.
ProtectHome=
Takes a boolean argument or "read-only". 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. 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. For this setting the same restrictions regarding mount propagation and privileges
apply as for ReadOnlyPaths= and related calls, see below.
RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=,
ConfigurationDirectory=
These options take a whitespace-separated list of directory names. The specified
directory names must be relative, and may not include "." or "..". If set, one or
more directories by the specified names will be created (including their parents)
below /run (or $XDG_RUNTIME_DIR for user services), /var/lib (or $XDG_CONFIG_HOME for
user services), /var/cache (or $XDG_CACHE_HOME for user services), /var/log (or
$XDG_CONFIG_HOME/log for user services), or /etc (or $XDG_CONFIG_HOME for user
services), respectively, when the unit is started.
In case of RuntimeDirectory= the lowest 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).
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.
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.
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).
Note that restricting access with these options does not extend to submounts of a
directory that are created later on. 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 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. 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.
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.
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.
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, this includes AF_NETLINK and AF_UNIX. The latter has
the effect that AF_UNIX sockets in the abstract socket namespace will become
unavailable to the processes (however, those located in the file system will continue
to be accessible).
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.
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.
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.
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.
ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading will be denied. This allows
to turn off module load and unload operations 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.
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.
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 familiy 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. 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.
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. 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.
MountFlags=
Takes a mount propagation flag: shared, slave or private, which control whether mounts
in the file system namespace set up for this unit's processes will receive or
propagate mounts and unmounts. See mount(2) for details. Defaults to shared. Use
shared to ensure that mounts and unmounts are propagated from systemd's namespace to
the service's namespace and vice versa. Use slave to run processes so that none of
their mounts and unmounts will propagate to the host. Use private to also ensure that
no mounts and unmounts from the host will propagate into the unit processes'
namespace. If this is set to slave or private, any mounts created by spawned processes
will be unmounted after the completion of the current command line of ExecStartPre=,
ExecStartPost=, ExecStart=, and ExecStopPost=. Note that slave means that file systems
mounted on the host might stay mounted continuously in the unit's namespace, and thus
keep the device busy. Note that the file system namespace related options
(PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=, ProtectKernelTunables=,
ProtectControlGroups=, ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=) require
that mount and unmount propagation from the unit's file system namespace is disabled,
and hence downgrade shared to slave.
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). 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. 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=. 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 2. 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) │
├───────────────┼──────────────────────────────────┤
│@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.
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=,
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. 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. Only system calls of the specified architectures will be
permitted to processes of this unit. This is an effective way to disable compatibility
with non-native architectures for processes, for example to prohibit execution of
32-bit x86 binaries on 64-bit x86-64 systems. The special native identifier implicitly
maps to the native architecture of the system (or more strictly: to the architecture
the system manager is compiled for). If running in user mode, or in system mode, but
without the CAP_SYS_ADMIN capability (e.g. setting User=nobody), NoNewPrivileges=yes
is implied. Note that setting this option to a non-empty list implies that native is
included too. By default, this option is set to the empty list, i.e. no system call
architecture filtering is applied.
Note that 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.
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 (").
The argument passed should be an absolute filename or wildcard expression, optionally
prefixed with "-", which indicates that if the file does not exist, it will not be
read and no error or warning message is logged. This option may be specified more than
once in which case all specified files are read. If the empty string is assigned to
this option, the list of file to read is reset, all prior assignments have no effect.
The files listed with this directive will be read shortly before the process is
executed (more specifically, after all processes from a previous unit state
terminated. This means you can generate these files in one unit state, and read it
with this option in the next).
Settings from these files override settings made with Environment=. If the same
variable is set twice from these files, the files will be read in the order they are
specified and the later setting will override the earlier setting.
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=.
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.
StandardOutput=
Controls where file descriptor 1 (STDOUT) of the executed processes is connected to.
Takes one of inherit, null, tty, journal, syslog, kmsg, journal+console,
syslog+console, kmsg+console, file: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 syslog or kmsg (see below) is
implicitly stored in the journal as well, the specific two options listed below are
hence supersets of this one.
syslog connects standard output to the syslog(3) system syslog service, in addition to
the journal. Note that the journal daemon is usually configured to forward everything
it receives to syslog anyway, in which case this option is no different from journal.
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, syslog+console and kmsg+console work in a similar way as the three
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 StandardInputText=, see above.
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 particular 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.
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, syslog 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 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[4]. 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 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.
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, syslog 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, syslog 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, syslog 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, syslog 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:
• 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)).
• Variables defined by the service manager itself (see the list below)
• Variables set in the service manager's own environment variable block (subject to
PassEnvironment= for the system service manager)
• Variables set via Environment= in the unit file
• Variables read from files specified via EnvironmentFile= in the unit file
• 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 by the service manager itself 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:/sbin:/bin.
$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 for volatile state. Set for the user systemd instance, and also in user
sessions. See pam_systemd(8).
$XDG_SESSION_ID, $XDG_SEAT, $XDG_VTNR
The identifier of the session, the seat name, and virtual terminal of the session. Set
by pam_systemd(8) for login sessions. $XDG_SEAT and $XDG_VTNR will only be set when
attached to a seat and a tty.
$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 3. 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 $EXIT_CODE is "exited", and the
signal name in all other cases. Note that these environment variables are only set if
the service manager succeeded to start and identify the main process of the service.
Table 4. Summary of possible service result variable values
┌──────────────────────┬─────────────────────┬─────────────────────────────┐
│$SERVICE_RESULT │$EXIT_CODE │ $EXIT_STATUS │
├──────────────────────┼─────────────────────┼─────────────────────────────┤
│"success" │"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" │
├──────────────────────┼─────────────────────┼─────────────────────────────┤
│"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. │
└──────────────────────────────────────────────────────────────────────────┘
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 5. 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[5].
Table 6. 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 7. 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. │
└──────────┴──────────────────────────────┴─────────────────────────────────────────────┘
SEE ALSO
systemd(1), systemctl(1), systemd-analyze(1), journalctl(8), 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://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/
2. No New Privileges Flag
https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html
3. proc.txt
https://www.kernel.org/doc/Documentation/filesystems/proc.txt
4. Base64
https://tools.ietf.org/html/rfc2045#section-6.8
5. LSB specification
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html