Provided by: systemd_229-4ubuntu21.31_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.
AUTOMATIC DEPENDENCIES
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 output standard output or error output is connected to any other sink but null, tty and
socket automatically acquire dependencies of type After= on journald.socket.
OPTIONS
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[1] 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=.
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=
These settings set both soft and hard limits of various resources for executed processes. See
setrlimit(2) for details. The resource limit is possible to specify in two formats, value to set soft
and hard limits to the same value, or 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 (=1024), M (=1024*1024) and so on for G, T, P and E 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.
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, on top of what Capabilities= does. 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.
Capabilities=
Controls the capabilities(7) set for the executed process. Take a capability string describing the
effective, permitted and inherited capability sets as documented in cap_from_text(3). Note that these
capability sets are usually influenced (and filtered) by the capabilities attached to the executed
file. Due to that CapabilityBoundingSet= is probably a much more useful setting.
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. 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.
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 and this option is used, 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 and this option is used, 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 and this option is used, 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 x86 and x86-64. This 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).
ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
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).
SEE ALSO
systemd(1), systemctl(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. proc.txt
https://www.kernel.org/doc/Documentation/filesystems/proc.txt