NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | OPTIONS | ENVIRONMENT VARIABLES IN SPAWNED PROCESSES | SEE ALSO | NOTES | COLOPHON

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

NAME         top

       systemd.exec - Execution environment configuration

SYNOPSIS         top

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

DESCRIPTION         top

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

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

       In addition, options which control resources through Linux Control
       Groups (cgroups) are listed in systemd.resource-control(5). Those
       options complement options listed here.

AUTOMATIC DEPENDENCIES         top

       A few execution parameters result in additional, automatic
       dependencies to be added.

       Units with WorkingDirectory=, RootDirectory= or RootImage= set
       automatically gain dependencies of type Requires= and After= on all
       mount units required to access the specified paths. This is
       equivalent to having them listed explicitly in RequiresMountsFor=.

       Similar, units with PrivateTmp= enabled automatically get mount unit
       dependencies for all mounts required to access /tmp and /var/tmp.
       They will also gain an automatic After= dependency on
       systemd-tmpfiles-setup.service(8).

       Units whose standard output or error output is connected to journal,
       syslog or kmsg (or their combinations with console output, see below)
       automatically acquire dependencies of type After= on
       systemd-journald.socket.

OPTIONS         top

       WorkingDirectory=
           Takes a directory path relative to the service's root directory
           specified by RootDirectory=, or the special value "~". Sets the
           working directory for executed processes. If set to "~", the home
           directory of the user specified in User= is used. If not set,
           defaults to the root directory when systemd is running as a
           system instance and the respective user's home directory if run
           as user. If the setting is prefixed with the "-" character, a
           missing working directory is not considered fatal. If
           RootDirectory=/RootImage= is not set, then WorkingDirectory= is
           relative to the root of the system running the service manager.
           Note that setting this parameter might result in additional
           dependencies to be added to the unit (see above).

       RootDirectory=
           Takes a directory path relative to the host's root directory
           (i.e. the root of the system running the service manager). Sets
           the root directory for executed processes, with the chroot(2)
           system call. If this is used, it must be ensured that the process
           binary and all its auxiliary files are available in the chroot()
           jail. Note that setting this parameter might result in additional
           dependencies to be added to the unit (see above).

           The MountAPIVFS= and PrivateUsers= settings are particularly
           useful in conjunction with RootDirectory=. For details, see
           below.

       RootImage=
           Takes a path to a block device node or regular file as argument.
           This call is similar to RootDirectory= however mounts a file
           system hierarchy from a block device node or loopback file
           instead of a directory. The device node or file system image file
           needs to contain a file system without a partition table, or a
           file system within an MBR/MS-DOS or GPT partition table with only
           a single Linux-compatible partition, or a set of file systems
           within a GPT partition table that follows the Discoverable
           Partitions Specification[1].

       MountAPIVFS=
           Takes a boolean argument. If on, a private mount namespace for
           the unit's processes is created and the API file systems /proc,
           /sys, and /dev are mounted inside of it, unless they are already
           mounted. Note that this option has no effect unless used in
           conjunction with RootDirectory=/RootImage= as these three mounts
           are generally mounted in the host anyway, and unless the root
           directory is changed, the private mount namespace will be a 1:1
           copy of the host's, and include these three mounts. Note that the
           /dev file system of the host is bind mounted if this option is
           used without PrivateDevices=. To run the service with a private,
           minimal version of /dev/, combine this option with
           PrivateDevices=.

       User=, Group=
           Set the UNIX user or group that the processes are executed as,
           respectively. Takes a single user or group name, or numeric ID as
           argument. For system services (services run by the system service
           manager, i.e. managed by PID 1) and for user services of the root
           user (services managed by root's instance of systemd --user), the
           default is "root", but User= may be used to specify a different
           user. For user services of any other user, switching user
           identity is not permitted, hence the only valid setting is the
           same user the user's service manager is running as. If no group
           is set, the default group of the user is used. This setting does
           not affect commands whose command line is prefixed with "+".

       DynamicUser=
           Takes a boolean parameter. If set, a UNIX user and group pair is
           allocated dynamically when the unit is started, and released as
           soon as it is stopped. The user and group will not be added to
           /etc/passwd or /etc/group, but are managed transiently during
           runtime. The nss-systemd(8) glibc NSS module provides integration
           of these dynamic users/groups into the system's user and group
           databases. The user and group name to use may be configured via
           User= and Group= (see above). If these options are not used and
           dynamic user/group allocation is enabled for a unit, the name of
           the dynamic user/group is implicitly derived from the unit name.
           If the unit name without the type suffix qualifies as valid user
           name it is used directly, otherwise a name incorporating a hash
           of it is used. If a statically allocated user or group of the
           configured name already exists, it is used and no dynamic
           user/group is allocated. Dynamic users/groups are allocated from
           the UID/GID range 61184...65519. It is recommended to avoid this
           range for regular system or login users. At any point in time
           each UID/GID from this range is only assigned to zero or one
           dynamically allocated users/groups in use. However, UID/GIDs are
           recycled after a unit is terminated. Care should be taken that
           any processes running as part of a unit for which dynamic
           users/groups are enabled do not leave files or directories owned
           by these users/groups around, as a different unit might get the
           same UID/GID assigned later on, and thus gain access to these
           files or directories. If DynamicUser= is enabled, RemoveIPC=,
           PrivateTmp= are implied. This ensures that the lifetime of IPC
           objects and temporary files created by the executed processes is
           bound to the runtime of the service, and hence the lifetime of
           the dynamic user/group. Since /tmp and /var/tmp are usually the
           only world-writable directories on a system this ensures that a
           unit making use of dynamic user/group allocation cannot leave
           files around after unit termination. Moreover
           ProtectSystem=strict and ProtectHome=read-only are implied, thus
           prohibiting the service to write to arbitrary file system
           locations. In order to allow the service to write to certain
           directories, they have to be whitelisted using ReadWritePaths=,
           but care must be taken so that UID/GID recycling doesn't create
           security issues involving files created by the service. Use
           RuntimeDirectory= (see below) in order to assign a writable
           runtime directory to a service, owned by the dynamic user/group
           and removed automatically when the unit is terminated. Defaults
           to off.

       SupplementaryGroups=
           Sets the supplementary Unix groups the processes are executed as.
           This takes a space-separated list of group names or IDs. This
           option may be specified more than once, in which case all listed
           groups are set as supplementary groups. When the empty string is
           assigned, the list of supplementary groups is reset, and all
           assignments prior to this one will have no effect. In any way,
           this option does not override, but extends the list of
           supplementary groups configured in the system group database for
           the user. This does not affect commands prefixed with "+".

       RemoveIPC=
           Takes a boolean parameter. If set, all System V and POSIX IPC
           objects owned by the user and group the processes of this unit
           are run as are removed when the unit is stopped. This setting
           only has an effect if at least one of User=, Group= and
           DynamicUser= are used. It has no effect on IPC objects owned by
           the root user. Specifically, this removes System V semaphores, as
           well as System V and POSIX shared memory segments and message
           queues. If multiple units use the same user or group the IPC
           objects are removed when the last of these units is stopped. This
           setting is implied if DynamicUser= is set.

       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[2] for
           details.

       IOSchedulingClass=
           Sets the I/O scheduling class for executed processes. Takes an
           integer between 0 and 3 or one of the strings none, realtime,
           best-effort or idle. See ioprio_set(2) for details.

       IOSchedulingPriority=
           Sets the I/O scheduling priority for executed processes. Takes an
           integer between 0 (highest priority) and 7 (lowest priority). The
           available priorities depend on the selected I/O scheduling class
           (see above). See ioprio_set(2) for details.

       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 or the equals sign to a
           variable, use double quotes (") for the assignment.

           Example:

               Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

           gives three variables "VAR1", "VAR2", "VAR3" with the values
           "word1 word2", "word3", "$word 5 6".

           See environ(7) for details about environment variables.

       EnvironmentFile=
           Similar to Environment= but reads the environment variables from
           a text file. The text file should contain new-line-separated
           variable assignments. Empty lines, lines without an "="
           separator, or lines starting with ; or # will be ignored, which
           may be used for commenting. A line ending with a backslash will
           be concatenated with the following one, allowing multiline
           variable definitions. The parser strips leading and trailing
           whitespace from the values of assignments, unless you use double
           quotes (").

           The argument passed should be an absolute filename or wildcard
           expression, optionally prefixed with "-", which indicates that if
           the file does not exist, it will not be read and no error or
           warning message is logged. This option may be specified more than
           once in which case all specified files are read. If the empty
           string is assigned to this option, the list of file to read is
           reset, all prior assignments have no effect.

           The files listed with this directive will be read shortly before
           the process is executed (more specifically, after all processes
           from a previous unit state terminated. This means you can
           generate these files in one unit state, and read it with this
           option in the next).

           Settings from these files override settings made with
           Environment=. If the same variable is set twice from these files,
           the files will be read in the order they are specified and the
           later setting will override the earlier setting.

       PassEnvironment=
           Pass environment variables 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, socket or fd.

           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.

           The fd option connects the input stream to a single file
           descriptor provided by a socket unit. A custom named file
           descriptor can be specified as part of this option, after a ":"
           (e.g.  "fd:foobar"). If no name is specified, "stdin" is assumed
           (i.e.  "fd" is equivalent to "fd:stdin"). At least one socket
           unit defining such name must be explicitly provided via the
           Sockets= option, and file descriptor name may differ from the
           name of its containing socket unit. If multiple matches are
           found, the first one will be used. See FileDescriptorName= in
           systemd.socket(5) for more details about named descriptors and
           ordering.

           This setting defaults to null.

       StandardOutput=
           Controls where file descriptor 1 (STDOUT) of the executed
           processes is connected to. Takes one of inherit, null, tty,
           journal, syslog, kmsg, journal+console, syslog+console,
           kmsg+console, socket or fd.

           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=.

           The fd option connects the output stream to a single file
           descriptor provided by a socket unit. A custom named file
           descriptor can be specified as part of this option, after a ":"
           (e.g.  "fd:foobar"). If no name is specified, "stdout" is assumed
           (i.e.  "fd" is equivalent to "fd:stdout"). At least one socket
           unit defining such name must be explicitly provided via the
           Sockets= option, and file descriptor name may differ from the
           name of its containing socket unit. If multiple matches are
           found, the first one will be used. See FileDescriptorName= in
           systemd.socket(5) for more details about named descriptors and
           ordering.

           If the standard output (or error output, see below) of a unit is
           connected to the journal, syslog or the kernel log buffer, the
           unit will implicitly gain a dependency of type After= on
           systemd-journald.socket (also see the automatic dependencies
           section above).

           This setting defaults to the value set with
           DefaultStandardOutput= in systemd-system.conf(5), which defaults
           to journal. Note that setting this parameter might result in
           additional dependencies to be added to the unit (see above).

       StandardError=
           Controls where file descriptor 2 (STDERR) of the executed
           processes is connected to. The available options are identical to
           those of StandardOutput=, with some exceptions: if set to inherit
           the file descriptor used for standard output is duplicated for
           standard error, while fd operates on the error stream and will
           look by default for a descriptor named "stderr".

           This setting defaults to the value set with DefaultStandardError=
           in systemd-system.conf(5), which defaults to inherit. Note that
           setting this parameter might result in additional dependencies to
           be added to the unit (see above).

       TTYPath=
           Sets the terminal device node to use if standard input, output,
           or error are connected to a TTY (see above). Defaults to
           /dev/console.

       TTYReset=
           Reset the terminal device specified with TTYPath= before and
           after execution. Defaults to "no".

       TTYVHangup=
           Disconnect all clients which have opened the terminal device
           specified with TTYPath= before and after execution. Defaults to
           "no".

       TTYVTDisallocate=
           If the terminal device specified with TTYPath= is a virtual
           console terminal, try to deallocate the TTY before and after
           execution. This ensures that the screen and scrollback buffer is
           cleared. Defaults to "no".

       SyslogIdentifier=
           Sets the process name to prefix log lines sent to the logging
           system or the kernel log buffer with. If not set, defaults to the
           process name of the executed process. This option is only useful
           when StandardOutput= or StandardError= are set to syslog, journal
           or kmsg (or to the same settings in combination with +console).

       SyslogFacility=
           Sets the syslog facility to use when logging to syslog. One of
           kern, user, mail, daemon, auth, syslog, lpr, news, uucp, cron,
           authpriv, ftp, local0, local1, local2, local3, local4, local5,
           local6 or local7. See syslog(3) for details. This option is only
           useful when StandardOutput= or StandardError= are set to syslog.
           Defaults to daemon.

       SyslogLevel=
           The default syslog level to use when logging to syslog or the
           kernel log buffer. One of emerg, alert, crit, err, warning,
           notice, info, debug. See syslog(3) for details. This option is
           only useful when StandardOutput= or StandardError= are set to
           syslog or kmsg. Note that individual lines output by the daemon
           might be prefixed with a different log level which can be used to
           override the default log level specified here. The interpretation
           of these prefixes may be disabled with SyslogLevelPrefix=, see
           below. For details, see sd-daemon(3). Defaults to info.

       SyslogLevelPrefix=
           Takes a boolean argument. If true and StandardOutput= or
           StandardError= are set to syslog, kmsg or journal, log lines
           written by the executed process that are prefixed with a log
           level will be passed on to syslog with this log level set but the
           prefix removed. If set to false, the interpretation of these
           prefixes is disabled and the logged lines are passed on as-is.
           For details about this prefixing see sd-daemon(3). Defaults to
           true.

       TimerSlackNSec=
           Sets the timer slack in nanoseconds for the executed processes.
           The timer slack controls the accuracy of wake-ups triggered by
           timers. See prctl(2) for more information. Note that in contrast
           to most other time span definitions this parameter takes an
           integer value in nano-seconds if no unit is specified. The usual
           time units are understood too.

       LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=,
       LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=,
       LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=,
       LimitRTPRIO=, LimitRTTIME=
           Set soft and hard limits on various resources for executed
           processes. See setrlimit(2) for details on the resource limit
           concept. Resource limits may be specified in two formats: either
           as single value to set a specific soft and hard limit to the same
           value, or as colon-separated pair soft:hard to set both limits
           individually (e.g.  "LimitAS=4G:16G"). Use the string infinity to
           configure no limit on a specific resource. The multiplicative
           suffixes K, M, G, T, P and E (to the base 1024) may be used for
           resource limits measured in bytes (e.g. LimitAS=16G). For the
           limits referring to time values, the usual time units ms, s, min,
           h and so on may be used (see systemd.time(7) for details). Note
           that if no time unit is specified for LimitCPU= the default unit
           of seconds is implied, while for LimitRTTIME= the default unit of
           microseconds is implied. Also, note that the effective
           granularity of the limits might influence their enforcement. For
           example, time limits specified for LimitCPU= will be rounded up
           implicitly to multiples of 1s. For LimitNICE= the value may be
           specified in two syntaxes: if prefixed with "+" or "-", the value
           is understood as regular Linux nice value in the range -20..19.
           If not prefixed like this the value is understood as raw resource
           limit parameter in the range 0..40 (with 0 being equivalent to
           1).

           Note that most process resource limits configured with these
           options are per-process, and processes may fork in order to
           acquire a new set of resources that are accounted independently
           of the original process, and may thus escape limits set. Also
           note that LimitRSS= is not implemented on Linux, and setting it
           has no effect. Often it is advisable to prefer the resource
           controls listed in systemd.resource-control(5) over these
           per-process limits, as they apply to services as a whole, may be
           altered dynamically at runtime, and are generally more
           expressive. For example, MemoryLimit= is a more powerful (and
           working) replacement for LimitRSS=.

           For system units these resource limits may be chosen freely. For
           user units however (i.e. units run by a per-user instance of
           systemd(1)), these limits are bound by (possibly more
           restrictive) per-user limits enforced by the OS.

           Resource limits not configured explicitly for a unit default to
           the value configured in the various DefaultLimitCPU=,
           DefaultLimitFSIZE=, ... options available in
           systemd-system.conf(5), and – if not configured there – the
           kernel or per-user defaults, as defined by the OS (the latter
           only for user services, see above).

           Table 1. Resource limit directives, their equivalent ulimit shell
           commands and the unit used
           ┌─────────────────┬───────────────────┬─────────────────────┐
           │Directive        ulimit equivalent │ Unit                │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitCPU=        │ ulimit -t         │ Seconds             │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitFSIZE=      │ ulimit -f         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitDATA=       │ ulimit -d         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitSTACK=      │ ulimit -s         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitCORE=       │ ulimit -c         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitRSS=        │ ulimit -m         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitNOFILE=     │ ulimit -n         │ Number of File      │
           │                 │                   │ Descriptors         │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitAS=         │ ulimit -v         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitNPROC=      │ ulimit -u         │ Number of Processes │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitMEMLOCK=    │ ulimit -l         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitLOCKS=      │ ulimit -x         │ Number of Locks     │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitSIGPENDING= │ ulimit -i         │ Number of Queued    │
           │                 │                   │ Signals             │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitMSGQUEUE=   │ ulimit -q         │ Bytes               │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitNICE=       │ ulimit -e         │ Nice Level          │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitRTPRIO=     │ ulimit -r         │ Realtime Priority   │
           ├─────────────────┼───────────────────┼─────────────────────┤
           │LimitRTTIME=     │ No equivalent     │ Microseconds        │
           └─────────────────┴───────────────────┴─────────────────────┘

       PAMName=
           Sets the PAM service name to set up a session as. If set, the
           executed process will be registered as a PAM session under the
           specified service name. This is only useful in conjunction with
           the User= setting, and is otherwise ignored. If not set, no PAM
           session will be opened for the executed processes. See pam(8) for
           details.

           Note that for each unit making use of this option a PAM session
           handler process will be maintained as part of the unit and stays
           around as long as the unit is active, to ensure that appropriate
           actions can be taken when the unit and hence the PAM session
           terminates. This process is named "(sd-pam)" and is an immediate
           child process of the unit's main process.

       CapabilityBoundingSet=
           Controls which capabilities to include in the capability bounding
           set for the executed process. See capabilities(7) for details.
           Takes a whitespace-separated list of capability names, e.g.
           CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities
           listed will be included in the bounding set, all others are
           removed. If the list of capabilities is prefixed with "~", all
           but the listed capabilities will be included, the effect of the
           assignment inverted. Note that this option also affects the
           respective capabilities in the effective, permitted and
           inheritable capability sets. If this option is not used, the
           capability bounding set is not modified on process execution,
           hence no limits on the capabilities of the process are enforced.
           This option may appear more than once, in which case the bounding
           sets are merged. If the empty string is assigned to this option,
           the bounding set is reset to the empty capability set, and all
           prior settings have no effect. If set to "~" (without any further
           argument), the bounding set is reset to the full set of available
           capabilities, also undoing any previous settings. This does not
           affect commands prefixed with "+".

       AmbientCapabilities=
           Controls which capabilities to include in the ambient capability
           set for the executed process. Takes a whitespace-separated list
           of capability names, e.g.  CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
           CAP_SYS_PTRACE. This option may appear more than once in which
           case the ambient capability sets are merged. If the list of
           capabilities is prefixed with "~", all but the listed
           capabilities will be included, the effect of the assignment
           inverted. If the empty string is assigned to this option, the
           ambient capability set is reset to the empty capability set, and
           all prior settings have no effect. If set to "~" (without any
           further argument), the ambient capability set is reset to the
           full set of available capabilities, also undoing any previous
           settings. Note that adding capabilities to ambient capability set
           adds them to the process's inherited capability set.

           Ambient capability sets are useful if you want to execute a
           process as a non-privileged user but still want to give it some
           capabilities. Note that in this case option keep-caps is
           automatically added to SecureBits= to retain the capabilities
           over the user change.  AmbientCapabilities= does not affect
           commands prefixed with "+".

       SecureBits=
           Controls the secure bits set for the executed process. Takes a
           space-separated combination of options from the following list:
           keep-caps, keep-caps-locked, no-setuid-fixup,
           no-setuid-fixup-locked, noroot, and noroot-locked. This option
           may appear more than once, in which case the secure bits are
           ORed. If the empty string is assigned to this option, the bits
           are reset to 0. This does not affect commands prefixed with "+".
           See capabilities(7) for details.

       ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=
           Sets up a new file system namespace for executed processes. These
           options may be used to limit access a process might have to the
           file system hierarchy. Each setting takes a space-separated list
           of paths relative to the host's root directory (i.e. the system
           running the service manager). Note that if paths contain
           symlinks, they are resolved relative to the root directory set
           with RootDirectory=/RootImage=.

           Paths listed in ReadWritePaths= are accessible from within the
           namespace with the same access modes as from outside of it. Paths
           listed in ReadOnlyPaths= are accessible for reading only, writing
           will be refused even if the usual file access controls would
           permit this. Nest ReadWritePaths= inside of ReadOnlyPaths= in
           order to provide writable subdirectories within read-only
           directories. Use ReadWritePaths= in order to whitelist specific
           paths for write access if ProtectSystem=strict is used. Paths
           listed in InaccessiblePaths= will be made inaccessible for
           processes inside the namespace (along with everything below them
           in the file system hierarchy).

           Note that restricting access with these options does not extend
           to submounts of a directory that are created later on.
           Non-directory paths may be specified as well. These options may
           be specified more than once, in which case all paths listed will
           have limited access from within the namespace. If the empty
           string is assigned to this option, the specific list is reset,
           and all prior assignments have no effect.

           Paths in ReadWritePaths=, ReadOnlyPaths= and InaccessiblePaths=
           may be prefixed with "-", in which case they will be ignored when
           they do not exist. If prefixed with "+" the paths are taken
           relative to the root directory of the unit, as configured with
           RootDirectory=/RootImage=, instead of relative to the root
           directory of the host (see above). When combining "-" and "+" on
           the same path make sure to specify "-" first, and "+" second.

           Note that using this setting will disconnect propagation of
           mounts from the service to the host (propagation in the opposite
           direction continues to work). This means that this setting may
           not be used for services which shall be able to install mount
           points in the main mount namespace. Note that the effect of these
           settings may be undone by privileged processes. In order to set
           up an effective sandboxed environment for a unit it is thus
           recommended to combine these settings with either
           CapabilityBoundingSet=~CAP_SYS_ADMIN or SystemCallFilter=~@mount.

       BindPaths=, BindReadOnlyPaths=
           Configures unit-specific bind mounts. A bind mount makes a
           particular file or directory available at an additional place in
           the unit's view of the file system. Any bind mounts created with
           this option are specific to the unit, and are not visible in the
           host's mount table. This option expects a whitespace separated
           list of bind mount definitions. Each definition consists of a
           colon-separated triple of source path, destination path and
           option string, where the latter two are optional. If only a
           source path is specified the source and destination is taken to
           be the same. The option string may be either "rbind" or "norbind"
           for configuring a recursive or non-recursive bind mount. If the
           destination path is omitted, the option string must be omitted
           too.

           BindPaths= creates regular writable bind mounts (unless the
           source file system mount is already marked read-only), while
           BindReadOnlyPaths= creates read-only bind mounts. These settings
           may be used more than once, each usage appends to the unit's list
           of bind mounts. If the empty string is assigned to either of
           these two options the entire list of bind mounts defined prior to
           this is reset. Note that in this case both read-only and regular
           bind mounts are reset, regardless which of the two settings is
           used.

           This option is particularly useful when RootDirectory=/RootImage=
           is used. In this case the source path refers to a path on the
           host file system, while the destination path refers to a path
           below the root directory of the unit.

       PrivateTmp=
           Takes a boolean argument. If true, sets up a new file system
           namespace for the executed processes and mounts private /tmp and
           /var/tmp directories inside it that is not shared by processes
           outside of the namespace. This is useful to secure access to
           temporary files of the process, but makes sharing between
           processes via /tmp or /var/tmp impossible. If this is enabled,
           all temporary files created by a service in these directories
           will be removed after the service is stopped. Defaults to false.
           It is possible to run two or more units within the same private
           /tmp and /var/tmp namespace by using the JoinsNamespaceOf=
           directive, see systemd.unit(5) for details. This setting is
           implied if DynamicUser= is set. For this setting the same
           restrictions regarding mount propagation and privileges apply as
           for ReadOnlyPaths= and related calls, see above. Enabling this
           setting has the side effect of adding Requires= and After=
           dependencies on all mount units necessary to access /tmp and
           /var/tmp. Moreover an implicitly After= ordering on
           systemd-tmpfiles-setup.service(8) is added.

       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,
           system memory /dev/mem, system ports /dev/port and others. This
           is useful to securely turn off physical device access by the
           executed process. Defaults to false. Enabling this option will
           install a system call filter to block low-level I/O system calls
           that are grouped in the @raw-io set, will also remove CAP_MKNOD
           and CAP_SYS_RAWIO from the capability bounding set for the unit
           (see above), and set DevicePolicy=closed (see
           systemd.resource-control(5) for details). Note that using this
           setting will disconnect propagation of mounts from the service to
           the host (propagation in the opposite direction continues to
           work). This means that this setting may not be used for services
           which shall be able to install mount points in the main mount
           namespace. The /dev namespace will be mounted read-only and
           'noexec'. The latter may break old programs which try to set up
           executable memory by using mmap(2) of /dev/zero instead of using
           MAP_ANON. This setting is implied if DynamicUser= is set. For
           this setting the same restrictions regarding mount propagation
           and privileges apply as for ReadOnlyPaths= and related calls, see
           above. If turned on and if running in user mode, or in system
           mode, but without the CAP_SYS_ADMIN capability (e.g. setting
           User=), NoNewPrivileges=yes is implied.

       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).

       PrivateUsers=
           Takes a boolean argument. If true, sets up a new user namespace
           for the executed processes and configures a minimal user and
           group mapping, that maps the "root" user and group as well as the
           unit's own user and group to themselves and everything else to
           the "nobody" user and group. This is useful to securely detach
           the user and group databases used by the unit from the rest of
           the system, and thus to create an effective sandbox environment.
           All files, directories, processes, IPC objects and other
           resources owned by users/groups not equaling "root" or the unit's
           own will stay visible from within the unit but appear owned by
           the "nobody" user and group. If this mode is enabled, all unit
           processes are run without privileges in the host user namespace
           (regardless if the unit's own user/group is "root" or not).
           Specifically this means that the process will have zero process
           capabilities on the host's user namespace, but full capabilities
           within the service's user namespace. Settings such as
           CapabilityBoundingSet= will affect only the latter, and there's
           no way to acquire additional capabilities in the host's user
           namespace. Defaults to off.

           This setting is particularly useful in conjunction with
           RootDirectory=/RootImage=, as the need to synchronize the user
           and group databases in the root directory and on the host is
           reduced, as the only users and groups who need to be matched are
           "root", "nobody" and the unit's own user and group.

       ProtectSystem=
           Takes a boolean argument or the special values "full" or
           "strict". If true, mounts the /usr and /boot directories
           read-only for processes invoked by this unit. If set to "full",
           the /etc directory is mounted read-only, too. If set to "strict"
           the entire file system hierarchy is mounted read-only, except for
           the API file system subtrees /dev, /proc and /sys (protect these
           directories using PrivateDevices=, ProtectKernelTunables=,
           ProtectControlGroups=). This setting ensures that any
           modification of the vendor-supplied operating system (and
           optionally its configuration, and local mounts) is prohibited for
           the service. It is recommended to enable this setting for all
           long-running services, unless they are involved with system
           updates or need to modify the operating system in other ways. If
           this option is used, ReadWritePaths= may be used to exclude
           specific directories from being made read-only. This setting is
           implied if DynamicUser= is set. For this setting the same
           restrictions regarding mount propagation and privileges apply as
           for ReadOnlyPaths= and related calls, see above. Defaults to off.

       ProtectHome=
           Takes a boolean argument or "read-only". If true, the directories
           /home, /root and /run/user are made inaccessible and empty for
           processes invoked by this unit. If set to "read-only", the three
           directories are made read-only instead. It is recommended to
           enable this setting for all long-running services (in particular
           network-facing ones), to ensure they cannot get access to private
           user data, unless the services actually require access to the
           user's private data. This setting is implied if DynamicUser= is
           set. For this setting the same restrictions regarding mount
           propagation and privileges apply as for ReadOnlyPaths= and
           related calls, see above.

       ProtectKernelTunables=
           Takes a boolean argument. If true, kernel variables accessible
           through /proc/sys, /sys, /proc/sysrq-trigger,
           /proc/latency_stats, /proc/acpi, /proc/timer_stats, /proc/fs and
           /proc/irq will be made read-only to all processes of the unit.
           Usually, tunable kernel variables should be initialized only at
           boot-time, for example with the sysctl.d(5) mechanism. Few
           services need to write to these at runtime; it is hence
           recommended to turn this on for most services. For this setting
           the same restrictions regarding mount propagation and privileges
           apply as for ReadOnlyPaths= and related calls, see above.
           Defaults to off. If turned on and if running in user mode, or in
           system mode, but without the CAP_SYS_ADMIN capability (e.g.
           services for which User= is set), NoNewPrivileges=yes is implied.
           Note that this option does not prevent indirect changes to kernel
           tunables effected by IPC calls to other processes. However,
           InaccessiblePaths= may be used to make relevant IPC file system
           objects inaccessible. If ProtectKernelTunables= is set,
           MountAPIVFS=yes is implied.

       ProtectKernelModules=
           Takes a boolean argument. If true, explicit module loading will
           be denied. This allows to turn off module load and unload
           operations on modular kernels. It is recommended to turn this on
           for most services that do not need special file systems or extra
           kernel modules to work. Default to off. Enabling this option
           removes CAP_SYS_MODULE from the capability bounding set for the
           unit, and installs a system call filter to block module system
           calls, also /usr/lib/modules is made inaccessible. For this
           setting the same restrictions regarding mount propagation and
           privileges apply as for ReadOnlyPaths= and related calls, see
           above. Note that limited automatic module loading due to user
           configuration or kernel mapping tables might still happen as side
           effect of requested user operations, both privileged and
           unprivileged. To disable module auto-load feature please see
           sysctl.d(5)kernel.modules_disabled mechanism and
           /proc/sys/kernel/modules_disabled documentation. If turned on and
           if running in user mode, or in system mode, but without the
           CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied.

       ProtectControlGroups=
           Takes a boolean argument. If true, the Linux Control Groups (‐
           cgroups(7)) hierarchies accessible through /sys/fs/cgroup will be
           made read-only to all processes of the unit. Except for container
           managers no services should require write access to the control
           groups hierarchies; it is hence recommended to turn this on for
           most services. For this setting the same restrictions regarding
           mount propagation and privileges apply as for ReadOnlyPaths= and
           related calls, see above. Defaults to off. If
           ProtectControlGroups= is set, MountAPIVFS=yes is implied.

       MountFlags=
           Takes a mount propagation flag: shared, slave or private, which
           control whether mounts in the file system namespace set up for
           this unit's processes will receive or propagate mounts and
           unmounts. See mount(2) for details. Defaults to shared. Use
           shared to ensure that mounts and unmounts are propagated from
           systemd's namespace to the service's namespace and vice versa.
           Use slave to run processes so that none of their mounts and
           unmounts will propagate to the host. Use private to also ensure
           that no mounts and unmounts from the host will propagate into the
           unit processes' namespace. If this is set to slave or private,
           any mounts created by spawned processes will be unmounted after
           the completion of the current command line of ExecStartPre=,
           ExecStartPost=, ExecStart=, and ExecStopPost=. Note that slave
           means that file systems mounted on the host might stay mounted
           continuously in the unit's namespace, and thus keep the device
           busy. Note that the file system namespace related options
           (PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
           ProtectKernelTunables=, ProtectControlGroups=, ReadOnlyPaths=,
           InaccessiblePaths=, ReadWritePaths=) require that mount and
           unmount propagation from the unit's file system namespace is
           disabled, and hence downgrade shared to slave.

       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. This does not affect commands prefixed with "+".
           See setexeccon(3) for details.

       AppArmorProfile=
           Takes a profile name as argument. The process executed by the
           unit will switch to this profile when started. Profiles must
           already be loaded in the kernel, or the unit will fail. This
           result in a non operation if AppArmor is not enabled. If prefixed
           by "-", all errors will be ignored. This does not affect commands
           prefixed with "+".

       SmackProcessLabel=
           Takes a SMACK64 security label as argument. The process executed
           by the unit will be started under this label and SMACK will
           decide whether the process is allowed to run or not, based on it.
           The process will continue to run under the label specified here
           unless the executable has its own SMACK64EXEC label, in which
           case the process will transition to run under that label. When
           not specified, the label that systemd is running under is used.
           This directive is ignored if SMACK is disabled.

           The value may be prefixed by "-", in which case all errors will
           be ignored. An empty value may be specified to unset previous
           assignments. This does not affect commands prefixed with "+".

       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
           through execve() (e.g. via setuid or setgid bits, or filesystem
           capabilities). This is the simplest and most effective way to
           ensure that a process and its children can never elevate
           privileges again. Defaults to false, but certain settings force
           NoNewPrivileges=yes, ignoring the value of this setting. This is
           the case when SystemCallFilter=, SystemCallArchitectures=,
           RestrictAddressFamilies=, RestrictNamespaces=, PrivateDevices=,
           ProtectKernelTunables=, ProtectKernelModules=,
           MemoryDenyWriteExecute=, or RestrictRealtime= are specified.

       SystemCallFilter=
           Takes a space-separated list of system call names. If this
           setting is used, all system calls executed by the unit processes
           except for the listed ones will result in immediate process
           termination with the SIGSYS signal (whitelisting). If the first
           character of the list is "~", the effect is inverted: only the
           listed system calls will result in immediate process termination
           (blacklisting). If running in user mode, or in system mode, but
           without the CAP_SYS_ADMIN capability (e.g. setting User=nobody),
           NoNewPrivileges=yes is implied. This feature makes use of the
           Secure Computing Mode 2 interfaces of the kernel ('seccomp
           filtering') and is useful for enforcing a minimal sandboxing
           environment. Note that the execve, exit, exit_group, getrlimit,
           rt_sigreturn, sigreturn system calls and the system calls for
           querying time and sleeping are implicitly whitelisted and do not
           need to be listed explicitly. This option may be specified more
           than once, in which case the filter masks are merged. If the
           empty string is assigned, the filter is reset, all prior
           assignments will have no effect. This does not affect commands
           prefixed with "+".

           Note that on systems supporting multiple ABIs (such as
           x86/x86-64) it is recommended to turn off alternative ABIs for
           services, so that they cannot be used to circumvent the
           restrictions of this option. Specifically, it is recommended to
           combine this option with SystemCallArchitectures=native or
           similar.

           Note that strict system call filters may impact execution and
           error handling code paths of the service invocation.
           Specifically, access to the execve system call is required for
           the execution of the service binary — if it is blocked service
           invocation will necessarily fail. Also, if execution of the
           service binary fails for some reason (for example: missing
           service executable), the error handling logic might require
           access to an additional set of system calls in order to process
           and log this failure correctly. It might be necessary to
           temporarily disable system call filters in order to simplify
           debugging of such failures.

           If you specify both types of this option (i.e. whitelisting and
           blacklisting), the first encountered will take precedence and
           will dictate the default action (termination or approval of a
           system call). Then the next occurrences of this option will add
           or delete the listed system calls from the set of the filtered
           system calls, depending of its type and the default action. (For
           example, if you have started with a whitelisting of read and
           write, and right after it add a blacklisting of write, then write
           will be removed from the set.)

           As the number of possible system calls is large, predefined sets
           of system calls are provided. A set starts with "@" character,
           followed by name of the set.

           Table 2. Currently predefined system call sets
           ┌───────────────┬───────────────────────────┐
           │Set            Description               │
           ├───────────────┼───────────────────────────┤
           │@basic-io      │ System calls for basic    │
           │               │ I/O: reading, writing,    │
           │               │ seeking, file descriptor  │
           │               │ duplication and closing   │
           │               │ (read(2), write(2), and   │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@clock         │ System calls for changing │
           │               │ the system clock (‐       │
           │               │ adjtimex(2),              │
           │               │ settimeofday(2), and      │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@cpu-emulation │ System calls for CPU      │
           │               │ emulation functionality   │
           │               │ (vm86(2) and related      │
           │               │ calls)                    │
           ├───────────────┼───────────────────────────┤
           │@debug         │ Debugging, performance    │
           │               │ monitoring and tracing    │
           │               │ functionality (ptrace(2), │
           │               │ perf_event_open(2) and    │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@file-system   │ File system operations:   │
           │               │ opening, creating files   │
           │               │ and directories for read  │
           │               │ and write, renaming and   │
           │               │ removing them, reading    │
           │               │ file properties, or       │
           │               │ creating hard and         │
           │               │ symbolic links.           │
           ├───────────────┼───────────────────────────┤
           │@io-event      │ Event loop system calls   │
           │               │ (poll(2), select(2),      │
           │               │ epoll(7), eventfd(2) and  │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@ipc           │ Pipes, SysV IPC, POSIX    │
           │               │ Message Queues and other  │
           │               │ IPC (mq_overview(7),      │
           │               │ svipc(7))                 │
           ├───────────────┼───────────────────────────┤
           │@keyring       │ Kernel keyring access (‐  │
           │               │ keyctl(2) and related     │
           │               │ calls)                    │
           ├───────────────┼───────────────────────────┤
           │@module        │ Loading and unloading of  │
           │               │ kernel modules (‐         │
           │               │ init_module(2),           │
           │               │ delete_module(2) and      │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@mount         │ Mounting and unmounting   │
           │               │ of file systems (‐        │
           │               │ mount(2), chroot(2), and  │
           │               │ related calls)            │
           ├───────────────┼───────────────────────────┤
           │@network-io    │ Socket I/O (including     │
           │               │ local AF_UNIX):           │
           │               │ socket(7), unix(7)        │
           ├───────────────┼───────────────────────────┤
           │@obsolete      │ Unusual, obsolete or      │
           │               │ unimplemented (‐          │
           │               │ create_module(2),         │
           │               │ gtty(2), ...)             │
           ├───────────────┼───────────────────────────┤
           │@privileged    │ All system calls which    │
           │               │ need super-user           │
           │               │ capabilities (‐           │
           │               │ capabilities(7))          │
           ├───────────────┼───────────────────────────┤
           │@process       │ Process control,          │
           │               │ execution, namespaceing   │
           │               │ operations (clone(2),     │
           │               │ kill(2), namespaces(7),   │
           │               │ ...                       │
           ├───────────────┼───────────────────────────┤
           │@raw-io        │ Raw I/O port access (‐    │
           │               │ ioperm(2), iopl(2),       │
           │               │ pciconfig_read(), ...)    │
           ├───────────────┼───────────────────────────┤
           │@reboot        │ System calls for          │
           │               │ rebooting and reboot      │
           │               │ preparation (reboot(2),   │
           │               │ kexec(), ...)             │
           ├───────────────┼───────────────────────────┤
           │@resources     │ System calls for changing │
           │               │ resource limits, memory   │
           │               │ and scheduling parameters │
           │               │ (setrlimit(2),            │
           │               │ setpriority(2), ...)      │
           ├───────────────┼───────────────────────────┤
           │@swap          │ System calls for          │
           │               │ enabling/disabling swap   │
           │               │ devices (swapon(2),       │
           │               │ swapoff(2))               │
           └───────────────┴───────────────────────────┘
           Note, that as new system calls are added to the kernel,
           additional system calls might be added to the groups above.
           Contents of the sets may also change between systemd versions. In
           addition, the list of system calls depends on the kernel version
           and architecture for which systemd was compiled. Use
           systemd-analyze syscall-filter to list the actual list of system
           calls in each filter.

           It is recommended to combine the file system namespacing related
           options with SystemCallFilter=~@mount, in order to prohibit the
           unit's processes to undo the mappings. Specifically these are the
           options PrivateTmp=, PrivateDevices=, ProtectSystem=,
           ProtectHome=, ProtectKernelTunables=, ProtectControlGroups=,
           ReadOnlyPaths=, InaccessiblePaths= and ReadWritePaths=.

       SystemCallErrorNumber=
           Takes an "errno" error number 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 the same as for ConditionArchitecture= described
           in systemd.unit(5), as well as x32, mips64-n32, mips64-le-n32,
           and the special identifier native. Only system calls of the
           specified architectures will be permitted to processes of this
           unit. This is an effective way to disable compatibility with
           non-native architectures for processes, for example to prohibit
           execution of 32-bit x86 binaries on 64-bit x86-64 systems. The
           special native identifier implicitly maps to the native
           architecture of the system (or more strictly: to the architecture
           the system manager is compiled for). If running in user mode, or
           in system mode, but without the CAP_SYS_ADMIN capability (e.g.
           setting User=nobody), NoNewPrivileges=yes is implied. Note that
           setting this option to a non-empty list implies that native is
           included too. By default, this option is set to the empty list,
           i.e. no system call architecture filtering is applied.

           Note that system call filtering is not equally effective on all
           architectures. For example, on x86 filtering of network
           socket-related calls is not possible, due to ABI limitations — a
           limitation that x86-64 does not have, however. On systems
           supporting multiple ABIs at the same time — such as x86/x86-64 —
           it is hence recommended to limit the set of permitted system call
           architectures so that secondary ABIs may not be used to
           circumvent the restrictions applied to the native ABI of the
           system. In particular, setting SystemCallFilter=native is a good
           choice for disabling non-native ABIs.

           System call architectures may also be restricted system-wide via
           the SystemCallArchitectures= option in the global configuration.
           See systemd-system.conf(5) for details.

       RestrictAddressFamilies=
           Restricts the set of socket address families accessible to the
           processes of this unit. Takes a space-separated list of address
           family names to whitelist, such as AF_UNIX, AF_INET or AF_INET6.
           When prefixed with ~ the listed address families will be applied
           as blacklist, otherwise as whitelist. Note that this restricts
           access to the socket(2) system call only. Sockets passed into the
           process by other means (for example, by using socket activation
           with socket units, see systemd.socket(5)) are unaffected. Also,
           sockets created with socketpair() (which creates connected
           AF_UNIX sockets only) are unaffected. Note that this option has
           no effect on 32-bit x86, s390, s390x, mips, mips-le, ppc, ppc-le,
           pcc64, ppc64-le and is ignored (but works correctly on other
           ABIs, including x86-64). Note that on systems supporting multiple
           ABIs (such as x86/x86-64) it is recommended to turn off
           alternative ABIs for services, so that they cannot be used to
           circumvent the restrictions of this option. Specifically, it is
           recommended to combine this option with
           SystemCallArchitectures=native or similar. If running in user
           mode, or in system mode, but without the CAP_SYS_ADMIN capability
           (e.g. setting User=nobody), NoNewPrivileges=yes is implied. By
           default, no restrictions apply, all address families are
           accessible to processes. If assigned the empty string, any
           previous address familiy restriction changes are undone. This
           setting does not affect commands prefixed with "+".

           Use this option to limit exposure of processes to remote access,
           in particular via exotic and sensitive network protocols, such as
           AF_PACKET. Note that in most cases, the local AF_UNIX address
           family should be included in the configured whitelist as it is
           frequently used for local communication, including for syslog(2)
           logging.

       RestrictNamespaces=
           Restricts access to Linux namespace functionality for the
           processes of this unit. For details about Linux namespaces, see
           namespaces(7). Either takes a boolean argument, or a
           space-separated list of namespace type identifiers. If false (the
           default), no restrictions on namespace creation and switching are
           made. If true, access to any kind of namespacing is prohibited.
           Otherwise, a space-separated list of namespace type identifiers
           must be specified, consisting of any combination of: cgroup, ipc,
           net, mnt, pid, user and uts. Any namespace type listed is made
           accessible to the unit's processes, access to namespace types not
           listed is prohibited (whitelisting). By prepending the list with
           a single tilda character ("~") the effect may be inverted: only
           the listed namespace types will be made inaccessible, all
           unlisted ones are permitted (blacklisting). If the empty string
           is assigned, the default namespace restrictions are applied,
           which is equivalent to false. Internally, this setting limits
           access to the unshare(2), clone(2) and setns(2) system calls,
           taking the specified flags parameters into account. Note that —
           if this option is used — in addition to restricting creation and
           switching of the specified types of namespaces (or all of them,
           if true) access to the setns() system call with a zero flags
           parameter is prohibited. This setting is only supported on x86,
           x86-64, mips, mips-le, mips64, mips64-le, mips64-n32,
           mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces no
           restrictions on other architectures. If running in user mode, or
           in system mode, but without the CAP_SYS_ADMIN capability (e.g.
           setting User=), NoNewPrivileges=yes is implied.

       Personality=
           Controls which kernel architecture uname(2) shall report, when
           invoked by unit processes. Takes one of the architecture
           identifiers x86, x86-64, ppc, ppc-le, ppc64, ppc64-le, s390 or
           s390x. Which personality architectures are supported depends on
           the system architecture. Usually the 64bit versions of the
           various system architectures support their immediate 32bit
           personality architecture counterpart, but no others. For example,
           x86-64 systems support the x86-64 and x86 personalities but no
           others. The personality feature is useful when running 32-bit
           services on a 64-bit host system. If not specified, the
           personality is left unmodified and thus reflects the personality
           of the host system's kernel.

       RuntimeDirectory=
           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).

       RuntimeDirectoryMode=
           Specifies the access mode of the directories specified in
           RuntimeDirectory= as an octal number. Defaults to 0755. See
           "Permissions" in path_resolution(7) for a discussion of the
           meaning of permission bits.

       MemoryDenyWriteExecute=
           Takes a boolean argument. If set, attempts to create memory
           mappings that are writable and executable at the same time, or to
           change existing memory mappings to become executable, or mapping
           shared memory segments as executable are prohibited.
           Specifically, a system call filter is added that rejects mmap(2)
           system calls with both PROT_EXEC and PROT_WRITE set, mprotect(2)
           system calls with PROT_EXEC set and shmat(2) system calls with
           SHM_EXEC set. Note that this option is incompatible with programs
           and libraries that generate program code dynamically at runtime,
           including JIT execution engines, executable stacks, and code
           "trampoline" feature of various C compilers. This option improves
           service security, as it makes harder for software exploits to
           change running code dynamically. Note that this feature is fully
           available on x86-64, and partially on x86. Specifically, the
           shmat() protection is not available on x86. Note that on systems
           supporting multiple ABIs (such as x86/x86-64) it is recommended
           to turn off alternative ABIs for services, so that they cannot be
           used to circumvent the restrictions of this option. Specifically,
           it is recommended to combine this option with
           SystemCallArchitectures=native or similar. If running in user
           mode, or in system mode, but without the CAP_SYS_ADMIN capability
           (e.g. setting User=), NoNewPrivileges=yes is implied.

       RestrictRealtime=
           Takes a boolean argument. If set, any attempts to enable realtime
           scheduling in a process of the unit are refused. This restricts
           access to realtime task scheduling policies such as SCHED_FIFO,
           SCHED_RR or SCHED_DEADLINE. See sched(7) for details about these
           scheduling policies. If running in user mode, or in system mode,
           but without the CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied. Realtime scheduling policies may
           be used to monopolize CPU time for longer periods of time, and
           may hence be used to lock up or otherwise trigger
           Denial-of-Service situations on the system. It is hence
           recommended to restrict access to realtime scheduling to the few
           programs that actually require them. Defaults to off.

ENVIRONMENT VARIABLES IN SPAWNED PROCESSES         top

       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).

       $INVOCATION_ID
           Contains a randomized, unique 128bit ID identifying each runtime
           cycle of the unit, formatted as 32 character hexadecimal string.
           A new ID is assigned each time the unit changes from an inactive
           state into an activating or active state, and may be used to
           identify this specific runtime cycle, in particular in data
           stored offline, such as the journal. The same ID is passed to all
           processes run as part of the unit.

       $XDG_RUNTIME_DIR
           The directory for volatile state. Set for the user systemd
           instance, and also in user sessions. See pam_systemd(8).

       $XDG_SESSION_ID, $XDG_SEAT, $XDG_VTNR
           The identifier of the session, the seat name, and virtual
           terminal of the session. Set by pam_systemd(8) for login
           sessions.  $XDG_SEAT and $XDG_VTNR will only be set when attached
           to a seat and a tty.

       $MAINPID
           The PID of the unit's main process if it is known. This is only
           set for control processes as invoked by ExecReload= and similar.

       $MANAGERPID
           The PID of the user systemd instance, set for processes spawned
           by it.

       $LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
           Information about file descriptors passed to a service for socket
           activation. See sd_listen_fds(3).

       $NOTIFY_SOCKET
           The socket sd_notify() talks to. See sd_notify(3).

       $WATCHDOG_PID, $WATCHDOG_USEC
           Information about watchdog keep-alive notifications. See
           sd_watchdog_enabled(3).

       $TERM
           Terminal type, set only for units connected to a terminal
           (StandardInput=tty, StandardOutput=tty, or StandardError=tty).
           See termcap(5).

       $JOURNAL_STREAM
           If the standard output or standard error output of the executed
           processes are connected to the journal (for example, by setting
           StandardError=journal) $JOURNAL_STREAM contains the device and
           inode numbers of the connection file descriptor, formatted in
           decimal, separated by a colon (":"). This permits invoked
           processes to safely detect whether their standard output or
           standard error output are connected to the journal. The device
           and inode numbers of the file descriptors should be compared with
           the values set in the environment variable to determine whether
           the process output is still connected to the journal. Note that
           it is generally not sufficient to only check whether
           $JOURNAL_STREAM is set at all as services might invoke external
           processes replacing their standard output or standard error
           output, without unsetting the environment variable.

           This environment variable is primarily useful to allow services
           to optionally upgrade their used log protocol to the native
           journal protocol (using sd_journal_print(3) and other functions)
           if their standard output or standard error output is connected to
           the journal anyway, thus enabling delivery of structured metadata
           along with logged messages.

       $SERVICE_RESULT
           Only defined for the service unit type, this environment variable
           is passed to all ExecStop= and ExecStopPost= processes, and
           encodes the service "result". Currently, the following values are
           defined: "protocol" (in case of a protocol violation; if a
           service did not take the steps required by its unit
           configuration), "timeout" (in case of an operation timeout),
           "exit-code" (if a service process exited with a non-zero exit
           code; see $EXIT_CODE below for the actual exit code returned),
           "signal" (if a service process was terminated abnormally by a
           signal; see $EXIT_CODE below for the actual signal used for the
           termination), "core-dump" (if a service process terminated
           abnormally and dumped core), "watchdog" (if the watchdog
           keep-alive ping was enabled for the service but it missed the
           deadline), or "resources" (a catch-all condition in case a system
           operation failed).

           This environment variable is useful to monitor failure or
           successful termination of a service. Even though this variable is
           available in both ExecStop= and ExecStopPost=, it is usually a
           better choice to place monitoring tools in the latter, as the
           former is only invoked for services that managed to start up
           correctly, and the latter covers both services that failed during
           their start-up and those which failed during their runtime.

       $EXIT_CODE, $EXIT_STATUS
           Only defined for the service unit type, these environment
           variables are passed to all ExecStop=, ExecStopPost= processes
           and contain exit status/code information of the main process of
           the service. For the precise definition of the exit code and
           status, see wait(2).  $EXIT_CODE is one of "exited", "killed",
           "dumped".  $EXIT_STATUS contains the numeric exit code formatted
           as string if $EXIT_CODE is "exited", and the signal name in all
           other cases. Note that these environment variables are only set
           if the service manager succeeded to start and identify the main
           process of the service.

           Table 3. Summary of possible service result variable values
           ┌──────────────────┬────────────────────┬─────────────────────┐
           │$SERVICE_RESULT$EXIT_CODE$EXIT_STATUS        │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"protocol"        │ not set            │ not set             │
           │                  ├────────────────────┼─────────────────────┤
           │                  │ "exited"           │ "0"                 │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"timeout"         │ "killed"           │ "TERM", "KILL"      │
           │                  ├────────────────────┼─────────────────────┤
           │                  │ "exited"           │ "0", "1", "2", "3", │
           │                  │                    │ ..., "255"          │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"exit-code"       │ "exited"           │ "0", "1", "2", "3", │
           │                  │                    │ ..., "255"          │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"signal"          │ "killed"           │ "HUP", "INT",       │
           │                  │                    │ "KILL", ...         │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"core-dump"       │ "dumped"           │ "ABRT", "SEGV",     │
           │                  │                    │ "QUIT", ...         │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"watchdog"        │ "dumped"           │ "ABRT"              │
           │                  ├────────────────────┼─────────────────────┤
           │                  │ "killed"           │ "TERM", "KILL"      │
           │                  ├────────────────────┼─────────────────────┤
           │                  │ "exited"           │ "0", "1", "2", "3", │
           │                  │                    │ ..., "255"          │
           ├──────────────────┼────────────────────┼─────────────────────┤
           │"resources"       │ any of the above   │ any of the above    │
           ├──────────────────┴────────────────────┼─────────────────────┤
           │Note: the process may be also          │                     │
           │terminated by a signal not sent by     │                     │
           │systemd. In particular the process may │                     │
           │send an arbitrary signal to itself in  │                     │
           │a handler for any of the non-maskable  │                     │
           │signals. Nevertheless, in the          │                     │
           │"timeout" and "watchdog" rows above    │                     │
           │only the signals that systemd sends    │                     │
           │have been included.                    │                     │
           └───────────────────────────────────────┴─────────────────────┘

       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         top

       systemd(1), systemctl(1), systemd-analyze(1), journalctl(8),
       systemd.unit(5), systemd.service(5), systemd.socket(5),
       systemd.swap(5), systemd.mount(5), systemd.kill(5),
       systemd.resource-control(5), systemd.time(7), systemd.directives(7),
       tmpfiles.d(5), exec(3)

NOTES         top

        1. Discoverable Partitions Specification
           https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/

        2. proc.txt
           https://www.kernel.org/doc/Documentation/filesystems/proc.txt

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see 
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository 
       ⟨https://github.com/systemd/systemd.git⟩ on 2017-09-15.  If you dis‐
       cover any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

systemd 234                                                  SYSTEMD.EXEC(5)

Pages that refer to this page: systemd(1)systemd-run(1)sd_bus_creds_get_pid(3)sd_id128_get_machine(3)systemd.kill(5)systemd.mount(5)systemd.resource-control(5)systemd.service(5)systemd.socket(5)systemd.swap(5)systemd-system.conf(5)systemd.unit(5)tmpfiles.d(5)daemon(7)systemd.directives(7)systemd.index(7)systemd.journal-fields(7)nss-systemd(8)systemd-coredump(8)