NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONCEPTS | DIRECTORIES | SIGNALS | ENVIRONMENT | KERNEL COMMAND LINE | SOCKETS AND FIFOS | SEE ALSO | NOTES | COLOPHON

SYSTEMD(1)                         systemd                        SYSTEMD(1)

NAME         top

       systemd, init - systemd system and service manager

SYNOPSIS         top

       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.

       For compatibility with SysV, if systemd is called as init and a PID
       that 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.

OPTIONS         top

       The following options are understood:

       --test
           Determine startup sequence, dump it and exit. This is an option
           useful for debugging only.

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

       --unit=
           Set default unit to activate on startup. If not specified,
           defaults to default.target.

       --system, --user
           For --system, tell systemd to run a system instance, even if the
           process ID is not 1, i.e. systemd is not run as init process.
           --user does the opposite, running a user instance even if the
           process ID is 1. Normally, it should not be necessary to pass
           these options, as systemd automatically detects the mode it is
           started in. These options are hence of little use except for
           debugging. Note that it is not supported booting and maintaining
           a full system with systemd running in --system mode, but PID not
           1. In practice, passing --system explicitly is only useful in
           conjunction with --test.

       --dump-core
           Enable core dumping on crash. This switch has no effect when
           running as user instance. This setting may also be enabled during
           boot on the kernel command line via the systemd.dump_core=
           option, see below.

       --crash-vt=VT
           Switch to a specific virtual console (VT) on crash. Takes a
           positive integer in the range 1–63, or a boolean argument. If an
           integer is passed, selects which VT to switch to. If yes, the VT
           kernel messages are written to is selected. If no, no VT switch
           is attempted. This switch has no effect when running as user
           instance. This setting may also be enabled during boot, on the
           kernel command line via the systemd.crash_vt= option, see below.

       --crash-shell
           Run a shell on crash. This switch has no effect when running as
           user instance. This setting may also be enabled during boot, on
           the kernel command line via the systemd.crash_shell= option, see
           below.

       --crash-reboot
           Automatically reboot the system on crash. This switch has no
           effect when running as user instance. This setting may also be
           enabled during boot, on the kernel command line via the
           systemd.crash_reboot= option, see below.

       --confirm-spawn
           Ask for confirmation when spawning processes. This switch has no
           effect when run as user instance.

       --show-status=
           Show terse service status information while booting. This switch
           has no effect when run as user instance. Takes a boolean argument
           which may be omitted which is interpreted as true.

       --log-target=
           Set log target. Argument must be one of console, journal, kmsg,
           journal-or-kmsg, null.

       --log-level=
           Set log level. As argument this accepts a numerical log level or
           the well-known syslog(3) symbolic names (lowercase): emerg,
           alert, crit, err, warning, notice, info, debug.

       --log-color=
           Highlight important log messages. Argument is a boolean value. If
           the argument is omitted, it defaults to true.

       --log-location=
           Include code location in log messages. This is mostly relevant
           for debugging purposes. Argument is a boolean value. If the
           argument is omitted it defaults to true.

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

       --machine-id=
           Override the machine-id set on the hard drive, useful for network
           booting or for containers. May not be set to all zeros.

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

       --version
           Print a short version string and exit.

CONCEPTS         top

       systemd provides a dependency system between various entities called
       "units" of 12 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, 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, or an
       operation timed out). 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 systemd.service(5).

        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 systemd.target(5).

        4. Device units expose kernel devices in systemd and may be used to
           implement device-based activation. For details, see
           systemd.device(5).

        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
           systemd.automount(5).

        7. Timer units are useful for triggering activation of other units
           based on timers. You may find details in systemd.timer(5).

        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 systemd.scope(5).

       Units are named as their configuration files. Some units have special
       semantics. A detailed list is available in systemd.special(7).

       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 default.target 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 graphical.target (for fully-featured boots into
       the UI) or multi-user.target (for limited console-only boots for use
       in embedded or server environments, or similar; a subset of
       graphical.target). 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.

       Processes systemd spawns are placed in individual Linux control
       groups named after the unit which they belong to in the private
       systemd hierarchy. (see cgroups.txt[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/systemd/), 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.

       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 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
       systemd.generator(7).

       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

       SIGTERM
           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 daemon-reexec.

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

       SIGINT
           Upon receiving this signal the systemd system manager will start
           the ctrl-alt-del.target unit. This is mostly equivalent to
           systemctl start ctl-alt-del.target. 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 2s is a relatively safe way to trigger an
           immediate reboot.

           systemd user managers treat this signal the same way as SIGTERM.

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

           This signal is ignored by systemd user managers.

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

       SIGUSR1
           When this signal is received the systemd manager will try to
           reconnect to the D-Bus bus.

       SIGUSR2
           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.

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

       SIGRTMIN+0
           Enters default mode, starts the default.target unit. This is
           mostly equivalent to systemctl start default.target.

       SIGRTMIN+1
           Enters rescue mode, starts the rescue.target unit. This is mostly
           equivalent to systemctl isolate rescue.target.

       SIGRTMIN+2
           Enters emergency mode, starts the emergency.service unit. This is
           mostly equivalent to systemctl isolate emergency.service.

       SIGRTMIN+3
           Halts the machine, starts the halt.target unit. This is mostly
           equivalent to systemctl start halt.target.

       SIGRTMIN+4
           Powers off the machine, starts the poweroff.target unit. This is
           mostly equivalent to systemctl start poweroff.target.

       SIGRTMIN+5
           Reboots the machine, starts the reboot.target unit. This is
           mostly equivalent to systemctl start reboot.target.

       SIGRTMIN+6
           Reboots the machine via kexec, starts the kexec.target unit. This
           is mostly equivalent to systemctl start kexec.target.

       SIGRTMIN+13
           Immediately halts the machine.

       SIGRTMIN+14
           Immediately powers off the machine.

       SIGRTMIN+15
           Immediately reboots the machine.

       SIGRTMIN+16
           Immediately reboots the machine with kexec.

       SIGRTMIN+20
           Enables display of status messages on the console, as controlled
           via systemd.show_status=1 on the kernel command line.

       SIGRTMIN+21
           Disables display of status messages on the console, as controlled
           via systemd.show_status=0 on the kernel command line.

       SIGRTMIN+22, SIGRTMIN+23
           Sets the log level to "debug" (or "info" on SIGRTMIN+23), as
           controlled via systemd.log_level=debug (or systemd.log_level=info
           on SIGRTMIN+23) on the kernel command line.

       SIGRTMIN+24
           Immediately exits the manager (only available for --user
           instances).

       SIGRTMIN+26, SIGRTMIN+27, SIGRTMIN+28
           Sets the log level to "journal-or-kmsg" (or "console" on
           SIGRTMIN+27, "kmsg" on SIGRTMIN+28), as controlled via
           systemd.log_target=journal-or-kmsg (or systemd.log_target=console
           on SIGRTMIN+27 or systemd.log_target=kmsg on SIGRTMIN+28) on the
           kernel command line.

ENVIRONMENT         top

       $SYSTEMD_LOG_LEVEL
           systemd reads the log level from this environment variable. This
           can be overridden with --log-level=.

       $SYSTEMD_LOG_TARGET
           systemd reads the log target from this environment variable. This
           can be overridden with --log-target=.

       $SYSTEMD_LOG_COLOR
           Controls whether systemd highlights important log messages. This
           can be overridden with --log-color=.

       $SYSTEMD_LOG_LOCATION
           Controls whether systemd prints the code location along with log
           messages. This can be overridden with --log-location=.

       $XDG_CONFIG_HOME, $XDG_CONFIG_DIRS, $XDG_DATA_HOME, $XDG_DATA_DIRS
           The systemd user manager uses these variables in accordance to
           the XDG Base Directory specification[6] to find its
           configuration.

       $SYSTEMD_UNIT_PATH
           Controls where systemd looks for unit files.

       $SYSTEMD_SYSVINIT_PATH
           Controls where systemd looks for SysV init scripts.

       $SYSTEMD_SYSVRCND_PATH
           Controls where systemd looks for SysV init script runlevel link
           farms.

       $SYSTEMD_COLORS
           Controls whether colorized output should be generated.

       $LISTEN_PID, $LISTEN_FDS, $LISTEN_FDNAMES
           Set by systemd for supervised processes during socket-based
           activation. See sd_listen_fds(3) for more information.

       $NOTIFY_SOCKET
           Set by systemd for supervised processes for status and start-up
           completion notification. See sd_notify(3) for more information.

KERNEL COMMAND LINE         top

       When run as system instance systemd parses a number of kernel command
       line arguments[7]:

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

       systemd.dump_core=
           Takes a boolean argument. If yes, the systemd manager (PID 1)
           dumps core when it crashes. Otherwise, no core dump is created.
           Defaults to yes.

       systemd.crash_chvt=
           Takes a positive integer, or a boolean argument. If a positive
           integer (in the range 1–63) is specified, the system manager (PID
           1) will activate the specified virtual terminal (VT) when it
           crashes. Defaults to no, meaning that no such switch is
           attempted. If set to yes, the VT the kernel messages are written
           to is selected.

       systemd.crash_shell=
           Takes a boolean argument. If yes, the system manager (PID 1)
           spawns a shell when it crashes, after a 10s delay. Otherwise, no
           shell is spawned. Defaults to no, for security reasons, as the
           shell is not protected by password authentication.

       systemd.crash_reboot=
           Takes a boolean argument. If yes, the system manager (PID 1) will
           reboot the machine automatically when it crashes, after a 10s
           delay. Otherwise, the system will hang indefinitely. Defaults to
           no, in order to avoid a reboot loop. If combined with
           systemd.crash_shell=, the system is rebooted after the shell
           exits.

       systemd.confirm_spawn=
           Takes a boolean argument. If yes, the system manager (PID 1) asks
           for confirmation when spawning processes. Defaults to no.

       systemd.show_status=
           Takes a boolean argument or the constant auto. If yes, the
           systemd manager (PID 1) shows terse service status updates on the
           console during bootup.  auto behaves like false until a service
           fails or there is a significant delay in boot. Defaults to yes,
           unless quiet is passed as kernel command line option, in which
           case it defaults to auto.

       systemd.log_target=, systemd.log_level=, systemd.log_color=,
       systemd.log_location=
           Controls log output, with the same effect as the
           $SYSTEMD_LOG_TARGET, $SYSTEMD_LOG_LEVEL, $SYSTEMD_LOG_COLOR,
           $SYSTEMD_LOG_LOCATION environment variables described above.

       systemd.default_standard_output=, systemd.default_standard_error=
           Controls default standard output and error output for services,
           with the same effect as the --default-standard-output= and
           --default-standard-error= command line arguments described above,
           respectively.

       systemd.setenv=
           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 variables.

       systemd.machine_id=
           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.

       quiet
           Turn off status output at boot, much like
           systemd.show_status=false 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.

       debug
           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.

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

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

       2, 3, 4, 5
           Boot into the specified legacy SysV runlevel. These are
           equivalent to systemd.unit=runlevel2.target,
           systemd.unit=runlevel3.target, systemd.unit=runlevel4.target, and
           systemd.unit=runlevel5.target, respectively, and provided for
           compatibility reasons and to be easier to type.

       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=, locale.LC_MEASUREMENT=,
       locale.LC_IDENTIFICATION=
           Set the system locale to use. This overrides the settings in
           /etc/locale.conf. For more information, see locale.conf(5) and
           locale(7).

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

SOCKETS AND FIFOS         top

       /run/systemd/notify
           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).

       /run/systemd/private
           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.

       /dev/initctl
           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.

SEE ALSO         top

       The systemd Homepage[8], systemd-system.conf(5), locale.conf(5),
       systemctl(1), journalctl(1), systemd-notify(1), daemon(7),
       sd-daemon(3), systemd.unit(5), systemd.special(5), pkg-config(1),
       kernel-command-line(7), bootup(7), systemd.directives(7)

NOTES         top

        1. cgroups.txt
           https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

        2. Original Design Document
           http://0pointer.de/blog/projects/systemd.html

        3. Interface Stability Promise
           http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise

        4. Container Interface
           http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface

        5. initrd Interface
           http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface

        6. XDG Base Directory specification
           http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

        7. If run inside a Linux container these arguments may be passed as
           command line arguments 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 instead.

        8. systemd Homepage
           http://www.freedesktop.org/wiki/Software/systemd/

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 2016-08-07.  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 231                                                       SYSTEMD(1)