<root
SYSTEMD.EXEC(5)                            systemd.exec                           SYSTEMD.EXEC(5)

NAME
       systemd.exec - Execution environment configuration

SYNOPSIS
       service.service, socket.socket, mount.mount, swap.swap

DESCRIPTION
       Unit configuration files for services, sockets, mount points, and swap devices share a
       subset of configuration options which define the execution environment of spawned
       processes.

       This man page lists the configuration options shared by these four unit types. See
       systemd.unit(5) for the common options of all unit configuration files, and
       systemd.service(5), systemd.socket(5), systemd.swap(5), and systemd.mount(5) for more
       information on the specific unit configuration files. The execution specific configuration
       options are configured in the [Service], [Socket], [Mount], or [Swap] sections, depending
       on the unit type.

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

systemd 229                                                                       SYSTEMD.EXEC(5)

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