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SYSTEMD(1)                                   systemd                                   SYSTEMD(1)



NAME
       systemd, init - systemd system and service manager

SYNOPSIS
       systemd [OPTIONS...]

       init [OPTIONS...] {COMMAND}

DESCRIPTION
       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. See systemd-system.conf(5) for more information.

OPTIONS
       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
           --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. Normally it should not be necessary to pass this
           options, as systemd automatically detects the mode it is started in. This option is
           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
           Dump core on crash.

       --crash-shell
           Run shell on crash.

       --confirm-spawn
           Ask for confirmation when spawning processes.

       --show-status=
           Show terse service status information while booting. 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.

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

       --version
           Print a short version string and exit.

CONCEPTS
       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. Snapshot units can be used to temporarily save the state of the set of systemd units,
           which later may be restored by activating the saved snapshot unit. For more
           information see systemd.snapshot(5).

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

        9. 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).

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

       11. 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).

       12. 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 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
       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).

       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
       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.

       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 often 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+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
       $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
           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
       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 true, systemd dumps core when it crashes. Otherwise, no
           core dump is created. Defaults to true.

       systemd.crash_shell=
           Takes a boolean argument. If true, systemd spawns a shell when it crashes. Otherwise,
           no shell is spawned. Defaults to false, for security reasons, as the shell is not
           protected by any password authentication.

       systemd.crash_chvt=
           Takes an integer argument. If positive systemd activates the specified virtual
           terminal when it crashes. Defaults to -1.

       systemd.confirm_spawn=
           Takes a boolean argument. If true, asks for confirmation when spawning processes.
           Defaults to false.

       systemd.show_status=
           Takes a boolean argument or the constant auto. If true, 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 true, 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.

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

       rescue, single, s, S, 1
           Boot into rescue mode. This is equivalent to systemd.unit=rescue.target 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
       /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/shutdownd
           Used internally by the shutdown(8) tool to implement delayed shutdowns. This is an
           AF_UNIX datagram socket.

       /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
       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
        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/



systemd 219                                                                            SYSTEMD(1)

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