systemd(1) — Linux manual page


SYSTEMD(1)                       systemd                      SYSTEMD(1)

NAME         top

       systemd, init - systemd system and service manager

SYNOPSIS         top

       /usr/lib/systemd/systemd [OPTIONS...]

       init [OPTIONS...] {COMMAND}

DESCRIPTION         top

       systemd is a system and service manager for Linux operating
       systems. When run as first process on boot (as PID 1), it acts as
       init system that brings up and maintains userspace services.
       Separate instances are started for logged-in users to start their

       systemd is usually not invoked directly by the user, but is
       installed as the /sbin/init symlink and started during early
       boot. The user manager instances are started automatically
       through the user@.service(5) service.

       For compatibility with SysV, if the binary is called as init and
       is not the first process on the machine (PID is not 1), it will
       execute telinit and pass all command line arguments unmodified.
       That means init and telinit are mostly equivalent when invoked
       from normal login sessions. See telinit(8) for more information.

       When run as a system instance, systemd interprets the
       configuration file system.conf and the files in system.conf.d
       directories; when run as a user instance, systemd interprets the
       configuration file user.conf and the files in user.conf.d
       directories. See systemd-system.conf(5) for more information.

CONCEPTS         top

       systemd provides a dependency system between various entities
       called "units" of 11 different types. Units encapsulate various
       objects that are relevant for system boot-up and maintenance. The
       majority of units are configured in unit configuration files,
       whose syntax and basic set of options is described in
       systemd.unit(5), however some are created automatically from
       other configuration files, dynamically from system state or
       programmatically at runtime. Units may be "active" (meaning
       started, bound, plugged in, ..., depending on the unit type, see
       below), or "inactive" (meaning stopped, unbound, unplugged, ...),
       as well as in the process of being activated or deactivated, i.e.
       between the two states (these states are called "activating",
       "deactivating"). A special "failed" state is available as well,
       which is very similar to "inactive" and is entered when the
       service failed in some way (process returned error code on exit,
       or crashed, an operation timed out, or after too many restarts).
       If this state is entered, the cause will be logged, for later
       reference. Note that the various unit types may have a number of
       additional substates, which are mapped to the five generalized
       unit states described here.

       The following unit types are available:

        1. Service units, which start and control daemons and the
           processes they consist of. For details, see

        2. Socket units, which encapsulate local IPC or network sockets
           in the system, useful for socket-based activation. For
           details about socket units, see systemd.socket(5), for
           details on socket-based activation and other forms of
           activation, see daemon(7).

        3. Target units are useful to group units, or provide well-known
           synchronization points during boot-up, see

        4. Device units expose kernel devices in systemd and may be used
           to implement device-based activation. For details, see

        5. Mount units control mount points in the file system, for
           details see systemd.mount(5).

        6. Automount units provide automount capabilities, for on-demand
           mounting of file systems as well as parallelized boot-up. See

        7. Timer units are useful for triggering activation of other
           units based on timers. You may find details in

        8. Swap units are very similar to mount units and encapsulate
           memory swap partitions or files of the operating system. They
           are described in systemd.swap(5).

        9. Path units may be used to activate other services when file
           system objects change or are modified. See systemd.path(5).

       10. Slice units may be used to group units which manage system
           processes (such as service and scope units) in a hierarchical
           tree for resource management purposes. See systemd.slice(5).

       11. Scope units are similar to service units, but manage foreign
           processes instead of starting them as well. See

       Units are named as their configuration files. Some units have
       special semantics. A detailed list is available in

       systemd knows various kinds of dependencies, including positive
       and negative requirement dependencies (i.e.  Requires= and
       Conflicts=) as well as ordering dependencies (After= and
       Before=). NB: ordering and requirement dependencies are
       orthogonal. If only a requirement dependency exists between two
       units (e.g.  foo.service requires bar.service), but no ordering
       dependency (e.g.  foo.service after bar.service) and both are
       requested to start, they will be started in parallel. It is a
       common pattern that both requirement and ordering dependencies
       are placed between two units. Also note that the majority of
       dependencies are implicitly created and maintained by systemd. In
       most cases, it should be unnecessary to declare additional
       dependencies manually, however it is possible to do this.

       Application programs and units (via dependencies) may request
       state changes of units. In systemd, these requests are
       encapsulated as 'jobs' and maintained in a job queue. Jobs may
       succeed or can fail, their execution is ordered based on the
       ordering dependencies of the units they have been scheduled for.

       On boot systemd activates the target unit whose
       job is to activate on-boot services and other on-boot units by
       pulling them in via dependencies. Usually, the unit name is just
       an alias (symlink) for either (for
       fully-featured boots into the UI) or (for
       limited console-only boots for use in embedded or server
       environments, or similar; a subset of However,
       it is at the discretion of the administrator to configure it as
       an alias to any other target unit. See systemd.special(7) for
       details about these target units.

       On first boot, systemd will enable or disable units according to
       preset policy. See systemd.preset(5) and "First Boot Semantics"
       in machine-id(5).

       systemd only keeps a minimal set of units loaded into memory.
       Specifically, the only units that are kept loaded into memory are
       those for which at least one of the following conditions is true:

        1. It is in an active, activating, deactivating or failed state
           (i.e. in any unit state except for "inactive")

        2. It has a job queued for it

        3. It is a dependency of at least one other unit that is loaded
           into memory

        4. It has some form of resource still allocated (e.g. a service
           unit that is inactive but for which a process is still
           lingering that ignored the request to be terminated)

        5. It has been pinned into memory programmatically by a D-Bus

       systemd will automatically and implicitly load units from disk —
       if they are not loaded yet — as soon as operations are requested
       for them. Thus, in many respects, the fact whether a unit is
       loaded or not is invisible to clients. Use systemctl list-units
       --all to comprehensively list all units currently loaded. Any
       unit for which none of the conditions above applies is promptly
       unloaded. Note that when a unit is unloaded from memory its
       accounting data is flushed out too. However, this data is
       generally not lost, as a journal log record is generated
       declaring the consumed resources whenever a unit shuts down.

       Processes systemd spawns are placed in individual Linux control
       groups named after the unit which they belong to in the private
       systemd hierarchy. (see Control Groups v2[1] for more information
       about control groups, or short "cgroups"). systemd uses this to
       effectively keep track of processes. Control group information is
       maintained in the kernel, and is accessible via the file system
       hierarchy (beneath /sys/fs/cgroup/), or in tools such as
       systemd-cgls(1) or ps(1) (ps xawf -eo pid,user,cgroup,args is
       particularly useful to list all processes and the systemd units
       they belong to.).

       systemd is compatible with the SysV init system to a large
       degree: SysV init scripts are supported and simply read as an
       alternative (though limited) configuration file format. The SysV
       /dev/initctl interface is provided, and compatibility
       implementations of the various SysV client tools are available.
       In addition to that, various established Unix functionality such
       as /etc/fstab or the utmp database are supported.

       systemd has a minimal transaction system: if a unit is requested
       to start up or shut down it will add it and all its dependencies
       to a temporary transaction. Then, it will verify if the
       transaction is consistent (i.e. whether the ordering of all units
       is cycle-free). If it is not, systemd will try to fix it up, and
       removes non-essential jobs from the transaction that might remove
       the loop. Also, systemd tries to suppress non-essential jobs in
       the transaction that would stop a running service. Finally it is
       checked whether the jobs of the transaction contradict jobs that
       have already been queued, and optionally the transaction is
       aborted then. If all worked out and the transaction is consistent
       and minimized in its impact it is merged with all already
       outstanding jobs and added to the run queue. Effectively this
       means that before executing a requested operation, systemd will
       verify that it makes sense, fixing it if possible, and only
       failing if it really cannot work.

       Note that transactions are generated independently of a unit's
       state at runtime, hence, for example, if a start job is requested
       on an already started unit, it will still generate a transaction
       and wake up any inactive dependencies (and cause propagation of
       other jobs as per the defined relationships). This is because the
       enqueued job is at the time of execution compared to the target
       unit's state and is marked successful and complete when both
       satisfy. However, this job also pulls in other dependencies due
       to the defined relationships and thus leads to, in our example,
       start jobs for any of those inactive units getting queued as

       systemd contains native implementations of various tasks that
       need to be executed as part of the boot process. For example, it
       sets the hostname or configures the loopback network device. It
       also sets up and mounts various API file systems, such as /sys/
       or /proc/.

       For more information about the concepts and ideas behind systemd,
       please refer to the Original Design Document[2].

       Note that some but not all interfaces provided by systemd are
       covered by the Interface Portability and Stability Promise[3].

       Units may be generated dynamically at boot and system manager
       reload time, for example based on other configuration files or
       parameters passed on the kernel command line. For details, see

       The D-Bus API of systemd is described in
       org.freedesktop.systemd1(5) and org.freedesktop.LogControl1(5).

       Systems which invoke systemd in a container or initrd environment
       should implement the Container Interface[4] or initrd
       Interface[5] specifications, respectively.

DIRECTORIES         top

       System unit directories
           The systemd system manager reads unit configuration from
           various directories. Packages that want to install unit files
           shall place them in the directory returned by pkg-config
           systemd --variable=systemdsystemunitdir. Other directories
           checked are /usr/local/lib/systemd/system and
           /usr/lib/systemd/system. User configuration always takes
           precedence.  pkg-config systemd
           --variable=systemdsystemconfdir returns the path of the
           system configuration directory. Packages should alter the
           content of these directories only with the enable and disable
           commands of the systemctl(1) tool. Full list of directories
           is provided in systemd.unit(5).

       User unit directories
           Similar rules apply for the user unit directories. However,
           here the XDG Base Directory specification[6] is followed to
           find units. Applications should place their unit files in the
           directory returned by pkg-config systemd
           --variable=systemduserunitdir. Global configuration is done
           in the directory reported by pkg-config systemd
           --variable=systemduserconfdir. The enable and disable
           commands of the systemctl(1) tool can handle both global
           (i.e. for all users) and private (for one user)
           enabling/disabling of units. Full list of directories is
           provided in systemd.unit(5).

       SysV init scripts directory
           The location of the SysV init script directory varies between
           distributions. If systemd cannot find a native unit file for
           a requested service, it will look for a SysV init script of
           the same name (with the .service suffix removed).

       SysV runlevel link farm directory
           The location of the SysV runlevel link farm directory varies
           between distributions. systemd will take the link farm into
           account when figuring out whether a service shall be enabled.
           Note that a service unit with a native unit configuration
           file cannot be started by activating it in the SysV runlevel
           link farm.

SIGNALS         top

       The service listens to various UNIX process signals that can be
       used to request various actions asynchronously. The signal
       handling is enabled very early during boot, before any further
       processes are invoked. However, a supervising container manager
       or similar that intends to request these operations via this
       mechanism must take into consideration that this functionality is
       not available during the earliest initialization phase. An
       sd_notify() notification message carrying the
       X_SYSTEMD_SIGNALS_LEVEL=2 field is emitted once the signal
       handlers are enabled, see below. This may be used to schedule
       submission of these signals correctly.

           Upon receiving this signal the systemd system manager
           serializes its state, reexecutes itself and deserializes the
           saved state again. This is mostly equivalent to systemctl

           systemd user managers will start the unit when
           this signal is received. This is mostly equivalent to
           systemctl --user start

           Upon receiving this signal the systemd system manager will
           start the unit. This is mostly equivalent
           to systemctl start
           --job-mode=replace-irreversibly. If this signal is received
           more than 7 times per 2s, an immediate reboot is triggered.
           Note that pressing Ctrl+Alt+Del on the console will trigger
           this signal. Hence, if a reboot is hanging, pressing
           Ctrl+Alt+Del more than 7 times in 2 seconds is a relatively
           safe way to trigger an immediate reboot.

           systemd user managers treat this signal the same way as

           When this signal is received the systemd system manager will
           start the unit. This is mostly equivalent to
           systemctl start

           This signal is ignored by systemd user managers.

           When this signal is received the systemd manager will start
           the unit. This is mostly equivalent to
           systemctl start

           When this signal is received the systemd manager will try to
           reconnect to the D-Bus bus.

           When this signal is received the systemd manager will log its
           complete state in human-readable form. The data logged is the
           same as printed by systemd-analyze dump.

           Reloads the complete daemon configuration. This is mostly
           equivalent to systemctl daemon-reload.

           Enters default mode, starts the unit. This is
           mostly equivalent to systemctl isolate

           Enters rescue mode, starts the unit. This is
           mostly equivalent to systemctl isolate

           Enters emergency mode, starts the emergency.service unit.
           This is mostly equivalent to systemctl isolate

           Halts the machine, starts the unit. This is
           mostly equivalent to systemctl start

           Powers off the machine, starts the unit. This
           is mostly equivalent to systemctl start

           Reboots the machine, starts the unit. This is
           mostly equivalent to systemctl start

           Reboots the machine via kexec, starts the unit.
           This is mostly equivalent to systemctl start

           Reboots userspace, starts the unit. This
           is mostly equivalent to systemctl start

           Added in version 254.

           Immediately halts the machine.

           Immediately powers off the machine.

           Immediately reboots the machine.

           Immediately reboots the machine with kexec.

           Immediately reboots the userspace.

           Added in version 254.

           Enables display of status messages on the console, as
           controlled via systemd.show_status=1 on the kernel command

           Disables display of status messages on the console, as
           controlled via systemd.show_status=0 on the kernel command

           Sets the service manager's log level to "debug", in a fashion
           equivalent to systemd.log_level=debug on the kernel command

           Restores the log level to its configured value. The
           configured value is derived from – in order of priority – the
           value specified with systemd.log-level= on the kernel command
           line, or the value specified with LogLevel= in the
           configuration file, or the built-in default of "info".

           Added in version 239.

           Immediately exits the manager (only available for --user

           Added in version 195.

           Upon receiving this signal the systemd manager will reexecute
           itself. This is mostly equivalent to systemctl daemon-reexec
           except that it will be done asynchronously.

           The systemd system manager treats this signal the same way as

           Added in version 250.

           Restores the log target to its configured value. The
           configured value is derived from – in order of priority – the
           value specified with systemd.log-target= on the kernel
           command line, or the value specified with LogTarget= in the
           configuration file, or the built-in default.

           Added in version 239.

           Sets the log target to "console" on SIGRTMIN+27 (or "kmsg" on
           SIGRTMIN+28), in a fashion equivalent to
           systemd.log_target=console (or systemd.log_target=kmsg on
           SIGRTMIN+28) on the kernel command line.

           Added in version 239.

ENVIRONMENT         top

       The environment block for the system manager is initially set by
       the kernel. (In particular, "key=value" assignments on the kernel
       command line are turned into environment variables for PID 1).
       For the user manager, the system manager sets the environment as
       described in the "Environment Variables in Spawned Processes"
       section of systemd.exec(5). The DefaultEnvironment= setting in
       the system manager applies to all services including
       user@.service. Additional entries may be configured (as for any
       other service) through the Environment= and EnvironmentFile=
       settings for user@.service (see systemd.exec(5)). Also,
       additional environment variables may be set through the
       ManagerEnvironment= setting in systemd-system.conf(5) and

       Some of the variables understood by systemd:

           The maximum log level of emitted messages (messages with a
           higher log level, i.e. less important ones, will be
           suppressed). Takes a comma-separated list of values. A value
           may be either one of (in order of decreasing importance)
           emerg, alert, crit, err, warning, notice, info, debug, or an
           integer in the range 0...7. See syslog(3) for more
           information. Each value may optionally be prefixed with one
           of console, syslog, kmsg or journal followed by a colon to
           set the maximum log level for that specific log target (e.g.
           SYSTEMD_LOG_LEVEL=debug,console:info specifies to log at
           debug level except when logging to the console which should
           be at info level). Note that the global maximum log level
           takes priority over any per target maximum log levels.

           This can be overridden with --log-level=.

           A boolean. If true, messages written to the tty will be
           colored according to priority.

           This can be overridden with --log-color=.

           A boolean. If true, console log messages will be prefixed
           with a timestamp.

           This can be overridden with --log-time=.

           Added in version 246.

           A boolean. If true, messages will be prefixed with a filename
           and line number in the source code where the message

           This can be overridden with --log-location=.

           A boolean. If true, messages will be prefixed with the
           current numerical thread ID (TID).

           Added in version 247.

           The destination for log messages. One of console (log to the
           attached tty), console-prefixed (log to the attached tty but
           with prefixes encoding the log level and "facility", see
           syslog(3), kmsg (log to the kernel circular log buffer),
           journal (log to the journal), journal-or-kmsg (log to the
           journal if available, and to kmsg otherwise), auto (determine
           the appropriate log target automatically, the default), null
           (disable log output).

           This can be overridden with --log-target=.

           Whether to ratelimit kmsg or not. Takes a boolean. Defaults
           to "true". If disabled, systemd will not ratelimit messages
           written to kmsg.

           Added in version 254.

           The systemd user manager uses these variables in accordance
           to the XDG Base Directory specification[6] to find its

           Controls where systemd looks for unit files and generators.

           These variables may contain a list of paths, separated by
           colons (":"). When set, if the list ends with an empty
           component ("...:"), this list is prepended to the usual set
           of paths. Otherwise, the specified list replaces the usual
           set of paths.

           Pager to use when --no-pager is not given; overrides $PAGER.
           If neither $SYSTEMD_PAGER nor $PAGER are set, a set of
           well-known pager implementations are tried in turn, including
           less(1) and more(1), until one is found. If no pager
           implementation is discovered no pager is invoked. Setting
           this environment variable to an empty string or the value
           "cat" is equivalent to passing --no-pager.

           Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER (as
           well as $PAGER) will be silently ignored.

           Override the options passed to less (by default "FRSXMK").

           Users might want to change two options in particular:

               This option instructs the pager to exit immediately when
               Ctrl+C is pressed. To allow less to handle Ctrl+C itself
               to switch back to the pager command prompt, unset this

               If the value of $SYSTEMD_LESS does not include "K", and
               the pager that is invoked is less, Ctrl+C will be ignored
               by the executable, and needs to be handled by the pager.

               This option instructs the pager to not send termcap
               initialization and deinitialization strings to the
               terminal. It is set by default to allow command output to
               remain visible in the terminal even after the pager
               exits. Nevertheless, this prevents some pager
               functionality from working, in particular paged output
               cannot be scrolled with the mouse.

           Note that setting the regular $LESS environment variable has
           no effect for less invocations by systemd tools.

           See less(1) for more discussion.

           Override the charset passed to less (by default "utf-8", if
           the invoking terminal is determined to be UTF-8 compatible).

           Note that setting the regular $LESSCHARSET environment
           variable has no effect for less invocations by systemd tools.

           Takes a boolean argument. When true, the "secure" mode of the
           pager is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE
           is not set at all, secure mode is enabled if the effective
           UID is not the same as the owner of the login session, see
           geteuid(2) and sd_pid_get_owner_uid(3). In secure mode,
           LESSSECURE=1 will be set when invoking the pager, and the
           pager shall disable commands that open or create new files or
           start new subprocesses. When $SYSTEMD_PAGERSECURE is not set
           at all, pagers which are not known to implement secure mode
           will not be used. (Currently only less(1) implements secure

           Note: when commands are invoked with elevated privileges, for
           example under sudo(8) or pkexec(1), care must be taken to
           ensure that unintended interactive features are not enabled.
           "Secure" mode for the pager may be enabled automatically as
           describe above. Setting SYSTEMD_PAGERSECURE=0 or not removing
           it from the inherited environment allows the user to invoke
           arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER
           variables are to be honoured, $SYSTEMD_PAGERSECURE must be
           set too. It might be reasonable to completely disable the
           pager using --no-pager instead.

           Takes a boolean argument. When true, systemd and related
           utilities will use colors in their output, otherwise the
           output will be monochrome. Additionally, the variable can
           take one of the following special values: "16", "256" to
           restrict the use of colors to the base 16 or 256 ANSI colors,
           respectively. This can be specified to override the automatic
           decision based on $TERM and what the console is connected to.

           The value must be a boolean. Controls whether clickable links
           should be generated in the output for terminal emulators
           supporting this. This can be specified to override the
           decision that systemd makes based on $TERM and other

           Set by systemd for supervised processes during socket-based
           activation. See sd_listen_fds(3) for more information.

           Set by service manager for its services for status and
           readiness notifications. Also consumed by service manager for
           notifying supervising container managers or service managers
           up the stack about its own progress. See sd_notify(3) and the
           relevant section below for more information.

       For further environment variables understood by systemd and its
       various components, see Known Environment Variables[7].


       When run as the system instance, systemd parses a number of
       options listed below. They can be specified as kernel command
       line arguments which are parsed from a number of sources
       depending on the environment in which systemd is executed. If run
       inside a Linux container, these options are parsed from the
       command line arguments passed to systemd itself, next to any of
       the command line options listed in the Options section above. If
       run outside of Linux containers, these arguments are parsed from
       /proc/cmdline and from the "SystemdOptions" EFI variable (on EFI
       systems) instead. Options from /proc/cmdline have higher

       Note: use of "SystemdOptions" is deprecated.

       The following variables are understood:

       systemd.unit=, rd.systemd.unit=
           Overrides the unit to activate on boot. Defaults to
  This may be used to temporarily boot into a
           different boot unit, for example or
           emergency.service. See systemd.special(7) for details about
           these units. The option prefixed with "rd."  is honored only
           in the initrd, while the one that is not prefixed only in the
           main system.

           Takes a boolean argument or enables the option if specified
           without an argument. If enabled, the systemd manager (PID 1)
           dumps core when it crashes. Otherwise, no core dump is
           created. Defaults to enabled.

           Added in version 233.

           Takes a positive integer, or a boolean argument. Can be also
           specified without an argument, with the same effect as a
           positive boolean. If a positive integer (in the range 1–63)
           is specified, the system manager (PID 1) will activate the
           specified virtual terminal when it crashes. Defaults to
           disabled, meaning that no such switch is attempted. If set to
           enabled, the virtual terminal the kernel messages are written
           to is used instead.

           Added in version 233.

           Takes a boolean argument or enables the option if specified
           without an argument. If enabled, the system manager (PID 1)
           spawns a shell when it crashes, after a 10s delay. Otherwise,
           no shell is spawned. Defaults to disabled, for security
           reasons, as the shell is not protected by password

           Added in version 233.

           Takes one of "freeze", "reboot" or "poweroff". Defaults to
           "freeze". If set to "freeze", the system will hang
           indefinitely when the system manager (PID 1) crashes. If set
           to "reboot", the system manager (PID 1) will reboot the
           machine automatically when it crashes, after a 10s delay. If
           set to "poweroff", the system manager (PID 1) will power off
           the machine immediately when it crashes. If combined with
           systemd.crash_shell, the configured crash action is executed
           after the shell exits.

           Added in version 256.

           Takes a boolean argument or a path to the virtual console
           where the confirmation messages should be emitted. Can be
           also specified without an argument, with the same effect as a
           positive boolean. If enabled, the system manager (PID 1) asks
           for confirmation when spawning processes using /dev/console.
           If a path or a console name (such as "ttyS0") is provided,
           the virtual console pointed to by this path or described by
           the give name will be used instead. Defaults to disabled.

           Added in version 233.

           Takes a boolean argument. If disabled, all service runtime
           watchdogs (WatchdogSec=) and emergency actions (e.g.
           OnFailure= or StartLimitAction=) are ignored by the system
           manager (PID 1); see systemd.service(5). Defaults to enabled,
           i.e. watchdogs and failure actions are processed normally.
           The hardware watchdog is not affected by this option.

           Added in version 237.

           Takes a boolean argument or the constants error and auto. Can
           be also specified without an argument, with the same effect
           as a positive boolean. If enabled, the systemd manager (PID
           1) shows terse service status updates on the console during
           bootup. With error, only messages about failures are shown,
           but boot is otherwise quiet.  auto behaves like false until
           there is a significant delay in boot. Defaults to enabled,
           unless quiet is passed as kernel command line option, in
           which case it defaults to error. If specified overrides the
           system manager configuration file option ShowStatus=, see

           Added in version 233.

           Takes name, description or combined as the value. If name,
           the system manager will use unit names in status messages. If
           combined, the system manager will use unit names and
           description in status messages. When specified, overrides the
           system manager configuration file option StatusUnitFormat=,
           see systemd-system.conf(5).

           Added in version 243.

       systemd.log_color, systemd.log_level=, systemd.log_location,
       systemd.log_target=, systemd.log_time, systemd.log_tid,
           Controls log output, with the same effect as the
           $SYSTEMD_LOG_RATELIMIT_KMSG environment variables described
           above.  systemd.log_color, systemd.log_location,
           systemd.log_time, systemd.log_tid and
           systemd.log_ratelimit_kmsg can be specified without an
           argument, with the same effect as a positive boolean.

       systemd.default_standard_output=, systemd.default_standard_error=
           Controls default standard output and error output for
           services and sockets. That is, controls the default for
           StandardOutput= and StandardError= (see systemd.exec(5) for
           details). Takes one of inherit, null, tty, journal,
           journal+console, kmsg, kmsg+console. If the argument is
           omitted systemd.default-standard-output= defaults to journal
           and systemd.default-standard-error= to inherit.

           Takes a string argument in the form VARIABLE=VALUE. May be
           used to set default environment variables to add to forked
           child processes. May be used more than once to set multiple

           Takes a 32 character hex value to be used for setting the
           machine-id. Intended mostly for network booting where the
           same machine-id is desired for every boot.

           Added in version 229.

       systemd.set_credential=, systemd.set_credential_binary=
           Sets a system credential, which can then be propagated to
           system services using the ImportCredential= or
           LoadCredential= setting, see systemd.exec(5) for details.
           Takes a pair of credential name and value, separated by a
           colon. The systemd.set_credential= parameter expects the
           credential value in literal text form, the
           systemd.set_credential_binary= parameter takes binary data
           encoded in Base64. Note that the kernel command line is
           typically accessible by unprivileged programs in
           /proc/cmdline. Thus, this mechanism is not suitable for
           transferring sensitive data. Use it only for data that is not
           sensitive (e.g. public keys/certificates, rather than private
           keys), or in testing/debugging environments.

           For further information see System and Service Credentials[8]

           Added in version 251.

           Takes a boolean argument. If false disables importing
           credentials from the kernel command line, the DMI/SMBIOS OEM
           string table, the qemu_fw_cfg subsystem or the EFI kernel

           Added in version 251.

           Turn off status output at boot, much like
           systemd.show_status=no would. Note that this option is also
           read by the kernel itself and disables kernel log output.
           Passing this option hence turns off the usual output from
           both the system manager and the kernel.

           Added in version 186.

           Turn on debugging output. This is equivalent to
           systemd.log_level=debug. Note that this option is also read
           by the kernel itself and enables kernel debug output. Passing
           this option hence turns on the debug output from both the
           system manager and the kernel.

           Added in version 205.

       emergency, rd.emergency, -b
           Boot into emergency mode. This is equivalent to
 , respectively, and provided
           for compatibility reasons and to be easier to type.

           Added in version 186.

       rescue, rd.rescue, single, s, S, 1
           Boot into rescue mode. This is equivalent to
           respectively, and provided for compatibility reasons and to
           be easier to type.

           Added in version 186.

       2, 3, 4, 5
           Boot into the specified legacy SysV runlevel. These are
           equivalent to,
           and, respectively, and provided
           for compatibility reasons and to be easier to type.

           Added in version 186.

       locale.LANG=, locale.LANGUAGE=, locale.LC_CTYPE=,
       locale.LC_NUMERIC=, locale.LC_TIME=, locale.LC_COLLATE=,
       locale.LC_MONETARY=, locale.LC_MESSAGES=, locale.LC_PAPER=,
       locale.LC_NAME=, locale.LC_ADDRESS=, locale.LC_TELEPHONE=,
           Set the system locale to use. This overrides the settings in
           /etc/locale.conf. For more information, see locale.conf(5)
           and locale(7).

           Added in version 186.

       For other kernel command line parameters understood by components
       of the core OS, please refer to kernel-command-line(7).


       During initialization the service manager will import credentials
       from various sources into the system's set of credentials, which
       can then be propagated into services and consumed by generators:

       •   When the service manager first initializes it will read
           system credentials from SMBIOS Type 11 vendor strings
           io.systemd.credential:name=value, and

       •   At the same time it will import credentials from QEMU
           "fw_cfg". (Note that the SMBIOS mechanism is generally
           preferred, because it is faster and generic.)

       •   Credentials may be passed via the kernel command line, using
           the systemd.set-credential= parameter, see above.

       •   Credentials may be passed from the UEFI environment via

       •   When the service manager is invoked during the initrd → host
           transition it will import all files in
           /run/credentials/@initrd/ as system credentials.

       Invoke systemd-creds(1) as follows to see the list of credentials
       passed into the system:

           # systemd-creds --system list

       For further information see System and Service Credentials[8]

       The service manager when run as PID 1 consumes the following
       system credentials:

           Contains a AF_VSOCK or AF_UNIX address where to send a
           READY=1 notification message when the service manager has
           completed booting. See sd_notify(3) and the next section for
           more information. Note that in case the hypervisor does not
           support SOCK_DGRAM over AF_VSOCK, SOCK_SEQPACKET will be
           tried instead. The credential payload for AF_VSOCK should be
           a string in the form "vsock:CID:PORT".  "vsock-stream",
           "vsock-dgram" and "vsock-seqpacket" can be used instead of
           "vsock" to force usage of the corresponding socket type.

           This feature is useful for machine managers or other
           processes on the host to receive a notification via VSOCK
           when a virtual machine has finished booting.

           Added in version 254.

           Takes a 128bit hexadecimal ID to initialize /etc/machine-id
           from, if the file is not set up yet. See machine-id(5) for

           Added in version 254.

       For a list of system credentials various other components of
       systemd consume, see systemd.system-credentials(7).


       The service manager implements a readiness notification protocol
       both between the manager and its services (i.e. down the stack),
       and between the manager and a potential supervisor further up the
       stack (the latter could be a machine or container manager, or in
       case of a per-user service manager the system service manager
       instance). The basic protocol (and the suggested API for it) is
       described in sd_notify(3).

       The notification socket the service manager (including PID 1)
       uses for reporting readiness to its own supervisor is set via the
       usual $NOTIFY_SOCKET environment variable (see above). Since this
       is directly settable only for container managers and for the
       per-user instance of the service manager, an additional mechanism
       to configure this is available, in particular intended for use in
       VM environments: the vmm.notify_socket system credential (see
       above) may be set to a suitable socket (typically an AF_VSOCK
       one) via SMBIOS Type 11 vendor strings. For details see above.

       The notification protocol from the service manager up the stack
       towards a supervisor supports a number of extension fields that
       allow a supervisor to learn about specific properties of the
       system and track its boot progress. Specifically the following
       fields are sent:

       •   An X_SYSTEMD_HOSTNAME=...  message will be sent out once the
           initial hostname for the system has been determined. Note
           that during later runtime the hostname might be changed again
           programmatically, and (currently) no further notifications
           are sent out in that case.

           Added in version 256.

       •   An X_SYSTEMD_MACHINE_ID=...  message will be sent out once
           the machine ID of the system has been determined. See
           machine-id(5) for details.

           Added in version 256.

       •   An X_SYSTEMD_SIGNALS_LEVEL=...  message will be sent out once
           the service manager installed the various UNIX process signal
           handlers described above. The field's value is an unsigned
           integer formatted as decimal string, and indicates the
           supported UNIX process signal feature level of the service
           manager. Currently, only a single feature level is defined:

           •   X_SYSTEMD_SIGNALS_LEVEL=2 covers the various UNIX process
               signals documented above – which are a superset of those
               supported by the historical SysV init system.

           Signals sent to PID 1 before this message is sent might not
           be handled correctly yet. A consumer of these messages should
           parse the value as an unsigned integer indication the level
           of support. For now only the mentioned level 2 is defined,
           but later on additional levels might be defined with higher
           integers, that will implement a superset of the currently
           defined behaviour.

           Added in version 256.

           messages will be sent out for each target unit as it becomes
           active or stops being active. This is useful to track boot
           progress and functionality. For example, once the
  unit is reported started SSH access is
           typically available, see systemd.special(7) for details.

           Added in version 256.

       •   An X_SYSTEMD_SHUTDOWN=...  message will be sent out very
           shortly before the system shuts down. The value is one of the
           strings "reboot", "halt", "poweroff", "kexec" and indicates
           which kind of shutdown is being executed.

           Added in version 256.

       •   An X_SYSTEMD_REBOOT_PARAMETER=...  message will also be sent
           out very shortly before the system shuts down. Its value is
           the reboot argument as configured with systemctl

           Added in version 256.

       Note that these extension fields are sent in addition to the
       regular "READY=1" and "RELOADING=1" notifications.

OPTIONS         top

       systemd is only very rarely invoked directly, since it is started
       early and is already running by the time users may interact with
       it. Normally, tools like systemctl(1) are used to give commands
       to the manager. Since systemd is usually not invoked directly,
       the options listed below are mostly useful for debugging and
       special purposes.

   Introspection and debugging options
       Those options are used for testing and introspection, and systemd
       may be invoked with them at any time:

           Dump understood unit configuration items. This outputs a
           terse but complete list of configuration items understood in
           unit definition files.

           Dump exposed bus properties. This outputs a terse but
           complete list of properties exposed on D-Bus.

           Added in version 239.

           Determine the initial start-up transaction (i.e. the list of
           jobs enqueued at start-up), dump it and exit — without
           actually executing any of the determined jobs. This option is
           useful for debugging only. Note that during regular service
           manager start-up additional units not shown by this operation
           may be started, because hardware, socket, bus or other kinds
           of activation might add additional jobs as the transaction is
           executed. Use --system to request the initial transaction of
           the system service manager (this is also the implied
           default), combine with --user to request the initial
           transaction of the per-user service manager instead.

       --system, --user
           When used in conjunction with --test, selects whether to
           calculate the initial transaction for the system instance or
           for a per-user instance. These options have no effect when
           invoked without --test, as during regular (i.e. non---test)
           invocations the service manager will automatically detect
           whether it shall operate in system or per-user mode, by
           checking whether the PID it is run as is 1 or not. Note that
           it is not supported booting and maintaining a system with the
           service manager running in --system mode but with a PID other
           than 1.

       -h, --help
           Print a short help text and exit.

           Print a short version string and exit.

   Options that duplicate kernel command line settings
       Those options correspond directly to options listed above in
       "Kernel Command Line". Both forms may be used equivalently for
       the system manager, but it is recommended to use the forms listed
       above in this context, because they are properly namespaced. When
       an option is specified both on the kernel command line and as a
       normal command line argument, the latter has higher precedence.

       When systemd is used as a user manager, the kernel command line
       is ignored and only the options described below are understood.
       Nevertheless, systemd is usually started in this mode through the
       user@.service(5) service, which is shared between all users. It
       may be more convenient to use configuration files to modify
       settings (see systemd-user.conf(5)), or environment variables.
       See the "Environment" section above for a discussion of how the
       environment block is set.

           Set default unit to activate on startup. If not specified,
           defaults to See systemd.unit= above.

           Enable core dumping on crash. This switch has no effect when
           running as user instance. Same as systemd.dump_core= above.

           Switch to a specific virtual console (VT) on crash. This
           switch has no effect when running as user instance. Same as
           systemd.crash_chvt= above (but not the different spelling!).

           Added in version 227.

           Run a shell on crash. This switch has no effect when running
           as user instance. See systemd.crash_shell= above.

           Specify what to do when the system manager (PID 1) crashes.
           This switch has no effect when systemd is running as user
           instance. See systemd.crash_action= above.

           Added in version 256.

           Ask for confirmation when spawning processes. This switch has
           no effect when run as user instance. See
           systemd.confirm_spawn above.

           Show terse unit status information on the console during
           boot-up and shutdown. See systemd.show_status above.

           Added in version 244.

           Highlight important log messages. See systemd.log_color

           Added in version 244.

           Set log level. See systemd.log_level above.

           Include code location in log messages. See
           systemd.log_location above.

           Added in version 244.

           Set log target. See systemd.log_target above.

           Prefix console messages with timestamp. See systemd.log_time

           Added in version 246.

           Override the machine-id set on the hard drive. See
           systemd.machine_id= above.

           Added in version 229.

           Globally enable/disable all service watchdog timeouts and
           emergency actions. See systemd.service_watchdogs above.

           Added in version 237.

       --default-standard-output=, --default-standard-error=
           Sets the default output or error output for all services and
           sockets, respectively. See systemd.default_standard_output=
           and systemd.default_standard_error= above.


           Daemon status notification socket. This is an AF_UNIX
           datagram socket and is used to implement the daemon
           notification logic as implemented by sd_notify(3).

           Used internally as communication channel between systemctl(1)
           and the systemd process. This is an AF_UNIX stream socket.
           This interface is private to systemd and should not be used
           in external projects.

           Limited compatibility support for the SysV client interface,
           as implemented by the systemd-initctl.service unit. This is a
           named pipe in the file system. This interface is obsolete and
           should not be used in new applications.

HISTORY         top

       systemd 252
           Kernel command-line arguments
           systemd.unified_cgroup_hierarchy and
           systemd.legacy_systemd_cgroup_controller were deprecated.
           Please switch to the unified cgroup hierarchy.

           Added in version 252.

SEE ALSO         top

       The systemd Homepage[9], systemd-system.conf(5), locale.conf(5),
       systemctl(1), journalctl(1), systemd-notify(1), daemon(7),
       sd-daemon(3), org.freedesktop.systemd1(5), systemd.unit(5),
       systemd.special(7), pkg-config(1), kernel-command-line(7),
       bootup(7), systemd.directives(7)

NOTES         top

        1. Control Groups v2

        2. Original Design Document

        3. Interface Portability and Stability Promise

        4. Container Interface

        5. initrd Interface

        6. XDG Base Directory specification

        7. Known Environment Variables

        8. System and Service Credentials

        9. systemd Homepage

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover 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

systemd 257~devel                                             SYSTEMD(1)

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