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