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.
The following options are understood:
Determine startup sequence, dump it and exit. This is an option
useful for debugging only.
Dump understood unit configuration items. This outputs a terse
but complete list of configuration items understood in unit
Set default unit to activate on startup. If not specified,
defaults to default.target.
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.
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.
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.
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
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.
Ask for confirmation when spawning processes. This switch has no
effect when run as user instance.
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.
Set log target. Argument must be one of console, journal, kmsg,
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.
Highlight important log messages. Argument is a boolean value. If
the argument is omitted, it defaults to true.
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.
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.
Override the machine-id set on the hard drive, useful for network
booting or for containers. May not be set to all zeros.
Print a short help text and exit.
Print a short version string and exit.
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
5. Mount units control mount points in the file system, for details
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 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 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.
Note that some but not all interfaces provided by systemd are covered
by the Interface Stability Promise.
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
Systems which invoke systemd in a container or initrd environment
should implement the Container Interface or initrd Interface
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
User unit directories
Similar rules apply for the user unit directories. However, here
the XDG Base Directory specification 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
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 --userstart exit.target.
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
systemd user managers treat this signal the same way as SIGTERM.
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.
When this signal is received the systemd manager will start the
sigpwr.target unit. This is mostly equivalent to systemctl startsigpwr.target.
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 default.target unit. This is
mostly equivalent to systemctl start default.target.
Enters rescue mode, starts the rescue.target unit. This is mostly
equivalent to systemctl isolate rescue.target.
Enters emergency mode, starts the emergency.service unit. This is
mostly equivalent to systemctl isolate emergency.service.
Halts the machine, starts the halt.target unit. This is mostly
equivalent to systemctl start halt.target.
Powers off the machine, starts the poweroff.target unit. This is
mostly equivalent to systemctl start poweroff.target.
Reboots the machine, starts the reboot.target unit. This is
mostly equivalent to systemctl start reboot.target.
Reboots the machine via kexec, starts the kexec.target unit. This
is mostly equivalent to systemctl start kexec.target.
Immediately halts the machine.
Immediately powers off the machine.
Immediately reboots the machine.
Immediately reboots the machine with kexec.
Enables display of status messages on the console, as controlled
via systemd.show_status=1 on the kernel command line.
Disables display of status messages on the console, as controlled
via systemd.show_status=0 on the kernel command line.
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.
Immediately exits the manager (only available for --user
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.
systemd reads the log level from this environment variable. This
can be overridden with --log-level=.
systemd reads the log target from this environment variable. This
can be overridden with --log-target=.
Controls whether systemd highlights important log messages. This
can be overridden with --log-color=.
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 to find its
Controls where systemd looks for unit files.
Controls where systemd looks for SysV init scripts.
Controls where systemd looks for SysV init script runlevel link
The value must be a boolean. Controls whether colorized output
should be generated. This can be specified to override the
decision that systemd makes based on $TERM and what the console
is connected to.
$LISTEN_PID, $LISTEN_FDS, $LISTEN_FDNAMES
Set by systemd for supervised processes during socket-based
activation. See sd_listen_fds(3) for more information.
Set by systemd for supervised processes for status and start-up
completion notification. See sd_notify(3) for more information.
When run as system instance systemd parses a number of kernel command
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.
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.
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.
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.
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
Takes a boolean argument. If yes, the system manager (PID 1) asks
for confirmation when spawning processes. Defaults to no.
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=,
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.
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,
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.
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.
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.
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
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=,
Set the system locale to use. This overrides the settings in
/etc/locale.conf. For more information, see locale.conf(5) and
For other kernel command line parameters understood by components of
the core OS, please refer to kernel-command-line(7).
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
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.
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
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2016-09-01. 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
systemd 231 SYSTEMD(1)