systemd.exec — Execution environment configuration
,
service
.service
,
socket
.socket
,
mount
.mountswap
.swap
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.
A few execution parameters result in additional, automatic dependencies to be added.
Units with WorkingDirectory=
or
RootDirectory=
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
.
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
.
WorkingDirectory=
¶Takes an absolute directory path, 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. Note that setting this parameter might result in
additional dependencies to be added to the unit (see
above).
RootDirectory=
¶Takes an absolute directory path. 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).
User=
, Group=
¶Sets the Unix user or group that the processes are executed as, respectively. Takes a single user or group name or ID as argument. If no group is set, the default group of the user is chosen.
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.
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.
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 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.
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.
UMask=
¶Controls the file mode creation mask. Takes an access mode in octal notation. See umask(2) for details. Defaults to 0022.
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 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 from the systemd system 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 set. If the empty string is assigned to this option, the list of environment variables is reset, all prior assignments have no effect. Variables that are not set in the system manager will not be passed and will be silently ignored.
Variables passed from this setting are overridden by those passed
from 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.
StandardInput=
¶Controls where file descriptor 0 (STDIN) of
the executed processes is connected to. Takes one of
null
,
tty
,
tty-force
,
tty-fail
or
socket
.
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 socket
option is only valid in
socket-activated services, and only when the socket
configuration file (see
systemd.socket(5)
for details) specifies a single socket only. If this option is
set, standard input will be connected to the socket the
service was activated from, which is primarily useful for
compatibility with daemons designed for use with the
traditional
inetd(8)
daemon.
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
or
socket
.
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.
socket
connects standard output to a
socket acquired via socket activation. The semantics are
similar to the same option of
StandardInput=
.
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 automatic dependencies section above).
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 one exception: if set to inherit
the
file descriptor used for standard output is duplicated for
standard error. 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).
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
".
SyslogIdentifier=
¶Sets the process name 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
syslog
, journal
or
kmsg
(or to the same settings in combination
with +console
).
SyslogFacility=
¶Sets the syslog facility to use when logging
to syslog. 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
syslog
. Defaults to
daemon
.
SyslogLevel=
¶The default syslog level to use when logging to
syslog 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
syslog
or kmsg
. Note that
individual lines output by the daemon might be prefixed with a
different log level which can be used to override the default
log level specified here. The interpretation of these prefixes
may be disabled with SyslogLevelPrefix=
,
see below. For details, see
sd-daemon(3).
Defaults to
info
.
SyslogLevelPrefix=
¶Takes a boolean argument. If true and
StandardOutput=
or
StandardError=
are set to
syslog
, kmsg
or
journal
, log lines written by the executed
process that are prefixed with a log level will be passed on
to syslog with this log level set but the prefix removed. If
set to false, the interpretation of these prefixes is disabled
and the logged lines are passed on as-is. For details about
this prefixing see
sd-daemon(3).
Defaults to true.
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.
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=
.
Table 1. Limit directives and their equivalent with ulimit
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 |
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. If
not set, no PAM session will be opened for the executed
processes. See
pam(8)
for details.
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 as read by cap_from_name(3),
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. 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.
AmbientCapabilities=
¶Controls which capabilities to include in the
ambient capability set for the executed process. Takes a
whitespace-separated list of capability names as read by
cap_from_name(3),
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.
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.
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. See
capabilities(7)
for details.
ReadWriteDirectories=
, ReadOnlyDirectories=
, InaccessibleDirectories=
¶Sets up a new file system namespace for
executed processes. These options may be used to limit access
a process might have to the main file system hierarchy. Each
setting takes a space-separated list of absolute directory
paths. Directories listed in
ReadWriteDirectories=
are accessible from
within the namespace with the same access rights as from
outside. Directories listed in
ReadOnlyDirectories=
are accessible for
reading only, writing will be refused even if the usual file
access controls would permit this. Directories listed in
InaccessibleDirectories=
will be made
inaccessible for processes inside the namespace, and may not
countain any other mountpoints, including those specified by
ReadWriteDirectories=
or
ReadOnlyDirectories=
.
Note that restricting access with these options does not extend
to submounts of a directory that are created later on. These
options may be specified more than once, in which case all
directories listed will have limited access from within the
namespace. If the empty string is assigned to this option, the
specific list is reset, and all prior assignments have no
effect.
Paths in
ReadOnlyDirectories=
and
InaccessibleDirectories=
may be prefixed with
"-
", in which case
they will be ignored when they do not
exist. Note that using this
setting will disconnect propagation of
mounts from the service to the host
(propagation in the opposite direction
continues to work). This means that
this setting may not be used for
services which shall be able to
install mount points in the main mount
namespace.
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. 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.
PrivateDevices=
¶Takes a boolean argument. If true, sets up a
new /dev namespace 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
. This is useful to securely turn
off physical device access by the executed process. Defaults
to false. Enabling this option will also remove
CAP_MKNOD
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 /dev namespace 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
.
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
securely turn off network access by the executed process.
Defaults to false. It is possible to run two or more units
within the same private network namespace by using the
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).
ProtectSystem=
¶Takes a boolean argument or
"full
". 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. This setting ensures that
any modification of the vendor-supplied operating system (and
optionally its configuration) is prohibited for the service.
It is recommended to enable this setting for all long-running
services, unless they are involved with system updates or need
to modify the operating system in other ways. Note however
that processes retaining the CAP_SYS_ADMIN capability can undo
the effect of this setting. This setting is hence particularly
useful for daemons which have this capability removed, for
example with CapabilityBoundingSet=
.
Defaults to off.
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. Note however that
processes retaining the CAP_SYS_ADMIN capability can undo the
effect of this setting. This setting is hence particularly
useful for daemons which have this capability removed, for
example with CapabilityBoundingSet=
.
Defaults to off.
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 or unmounts. See
mount(2)
for details. Defaults to shared
. Use
shared
to ensure that mounts and unmounts are
propagated from the host to the container 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. 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=
,
ReadOnlyDirectories=
,
InaccessibleDirectories=
and
ReadWriteDirectories=
) require that mount
and unmount propagation from the unit's file system namespace
is disabled, and hence downgrade shared
to
slave
.
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
".
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. 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.
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.
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.
NoNewPrivileges=
¶Takes a boolean argument. If true, ensures that the service process and all its children can never gain new privileges. This option is more powerful than the respective secure bits flags (see above), as it also prohibits UID changes of any kind. This is the simplest, most effective way to ensure that a process and its children can never elevate privileges again.
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). If running in
user mode, or in system mode, but without the
CAP_SYS_ADMIN
capabiblity (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
,
rt_sigreturn
,
sigreturn
,
exit_group
, exit
system calls are implicitly whitelisted and do not need to be
listed explicitly. This option may be specified more than once,
in which case the filter masks are merged. If the empty string
is assigned, the filter is reset, all prior assignments will
have no effect.
If you specify both types of this option (i.e.
whitelisting and blacklisting), the first encountered will
take precedence and will dictate the default action
(termination or approval of a system call). Then the next
occurrences of this option will add or delete the listed
system calls from the set of the filtered system calls,
depending of its type and the default action. (For example, if
you have started with a whitelisting of
read
and write
, and
right after it add a blacklisting of
write
, then write
will be removed from the set.)
SystemCallErrorNumber=
¶Takes an "errno
" error number
name to return when the system call filter configured with
SystemCallFilter=
is triggered, instead of
terminating the process immediately. Takes an error name such
as EPERM
, EACCES
or
EUCLEAN
. When this setting is not used,
or when the empty string is assigned, the process will be
terminated immediately when the filter is
triggered.
SystemCallArchitectures=
¶Takes a space-separated list of architecture
identifiers to include in the system call filter. The known
architecture identifiers are x86
,
x86-64
, x32
,
arm
as well as the special identifier
native
. Only system calls of the
specified architectures will be permitted to processes of this
unit. This is an effective way to disable compatibility with
non-native architectures for processes, for example to
prohibit execution of 32-bit x86 binaries on 64-bit x86-64
systems. The special 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
capabiblity (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 architecture system
call filtering is applied.
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 and is ignored (but works
correctly on x86-64). If running in user mode, or in system
mode, but without the CAP_SYS_ADMIN
capabiblity (e.g. setting User=nobody
),
NoNewPrivileges=yes
is implied. By
default, no restriction applies, all address families are
accessible to processes. If assigned the empty string, any
previous list changes are undone.
Use this option to limit exposure of processes to remote
systems, in particular via exotic network protocols. Note that
in most cases, the local AF_UNIX
address
family should be included in the configured whitelist as it is
frequently used for local communication, including for
syslog(2)
logging.
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.
RuntimeDirectory=
, RuntimeDirectoryMode=
¶Takes a list of directory names. If set, one
or more directories by the specified names will be created
below /run
(for system services) or below
$XDG_RUNTIME_DIR
(for user services) when
the unit is started, and removed when the unit is stopped. The
directories will have the access mode specified in
RuntimeDirectoryMode=
, and will be owned by
the user and group specified in User=
and
Group=
. Use this to manage one or more
runtime directories of the unit and bind their lifetime to the
daemon runtime. The specified directory names must be
relative, and may not include a "/
", i.e.
must refer to simple directories to create or remove. This is
particularly useful for unprivileged daemons that cannot
create runtime directories in /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).
Processes started by the system are executed in a clean environment in which select variables listed below are set. System processes started by systemd do not inherit variables from PID 1, but processes started by user systemd instances inherit all environment variables from the user systemd instance.
$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).
$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 units 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).
Additional variables may be configured by the following
means: for processes spawned in specific units, use the
Environment=
, EnvironmentFile=
and PassEnvironment=
options above; to specify
variables globally, use DefaultEnvironment=
(see
systemd-system.conf(5))
or the kernel option systemd.setenv=
(see
systemd(1)).
Additional variables may also be set through PAM,
cf. pam_env(8).