SYSTEMD(1) systemd SYSTEMD(1)
NAME
systemd, init - systemd system and service manager
SYNOPSIS
/lib/systemd/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. Separate instances are
started for logged-in users to start their services.
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
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, 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 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.
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 some sort 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 call
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 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.
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 our example, start jobs for any of those inactive units
getting queued as well.
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 /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
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 --job-mode=replace-irreversibly.
SIGINT
Upon receiving this signal the systemd system manager will start
the ctrl-alt-del.target unit. This is mostly equivalent to
systemctl start ctrl-alt-del.target
--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 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 isolate 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
--job-mode=replace-irreversibly.
SIGRTMIN+4
Powers off the machine, starts the poweroff.target unit. This is
mostly equivalent to systemctl start poweroff.target
--job-mode=replace-irreversibly.
SIGRTMIN+5
Reboots the machine, starts the reboot.target unit. This is mostly
equivalent to systemctl start reboot.target
--job-mode=replace-irreversibly.
SIGRTMIN+6
Reboots the machine via kexec, starts the kexec.target unit. This
is mostly equivalent to systemctl start kexec.target
--job-mode=replace-irreversibly.
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
Sets the service manager's log level to "debug", in a fashion
equivalent to systemd.log_level=debug on the kernel command line.
SIGRTMIN+23
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".
SIGRTMIN+24
Immediately exits the manager (only available for --user
instances).
SIGRTMIN+26
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.
SIGRTMIN+27, SIGRTMIN+28
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.
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_PAGER
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.
$SYSTEMD_LESS
Override the options passed to less (by default "FRSXMK").
Users might want to change two options in particular:
K
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 option.
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.
X
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.
See less(1) for more discussion.
$SYSTEMD_LESSCHARSET
Override the charset passed to less (by default "utf-8", if the
invoking terminal is determined to be UTF-8 compatible).
$SYSTEMD_COLORS
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.
$SYSTEMD_URLIFY
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 conditions.
$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.
For further environment variables understood by systemd and its various
components, see Known Environment Variables[7].
KERNEL COMMAND LINE
When run as the system instance systemd parses a number of options
listed below. They can be specified as kernel command line
arguments[8], or through the "SystemdOptions" EFI variable (on EFI
systems). The kernel command line has higher priority. Following
variables are understood:
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 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.
systemd.crash_chvt
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 (VT) when it crashes. Defaults to disabled, meaning that
no such switch is attempted. If set to enabled, the VT the kernel
messages are written to is selected.
systemd.crash_shell
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 authentication.
systemd.crash_reboot
Takes a boolean argument or enables the option if specified without
an argument. If enabled, 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 disabled,
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 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.
systemd.service_watchdogs=
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.
systemd.show_status
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 systemd-system.conf(5).
systemd.status_unit_format=
Takes either name or description as the value. If name, the system
manager will use unit names in status messages. If specified,
overrides the system manager configuration file option
StatusUnitFormat=, see systemd-system.conf(5).
systemd.log_target=, systemd.log_level=, systemd.log_location=,
systemd.log_color
Controls log output, with the same effect as the
$SYSTEMD_LOG_TARGET, $SYSTEMD_LOG_LEVEL, $SYSTEMD_LOG_LOCATION,
$SYSTEMD_LOG_COLOR environment variables described above.
systemd.log_color 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.
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.
systemd.unified_cgroup_hierarchy
When specified without an argument or with a true argument, enables
the usage of unified cgroup hierarchy[9] (a.k.a. cgroups-v2). When
specified with a false argument, fall back to hybrid or full legacy
cgroup hierarchy.
If this option is not specified, the default behaviour is
determined during compilation (the -Ddefault-hierarchy= meson
option). If the kernel does not support unified cgroup hierarchy,
the legacy hierarchy will be used even if this option is specified.
systemd.legacy_systemd_cgroup_controller
Takes effect if the full unified cgroup hierarchy is not used (see
previous option). When specified without an argument or with a true
argument, disables the use of "hybrid" cgroup hierarchy (i.e. a
cgroups-v2 tree used for systemd, and legacy cgroup hierarchy[10],
a.k.a. cgroups-v1, for other controllers), and forces a full
"legacy" mode. When specified with a false argument, enables the
use of "hybrid" hierarchy.
If this option is not specified, the default behaviour is
determined during compilation (the -Ddefault-hierarchy= meson
option). If the kernel does not support unified cgroup hierarchy,
the legacy hierarchy will be used even if this option is specified.
quiet
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.
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).
OPTIONS
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-configuration-items
Dump understood unit configuration items. This outputs a terse but
complete list of configuration items understood in unit definition
files.
--dump-bus-properties
Dump exposed bus properties. This outputs a terse but complete list
of properties exposed on D-Bus.
--test
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.
--version
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 a user manager, the kernel command line is ignored
and the options described are understood. Nevertheless, systemd is
usually started in this mode through the user@.service(5) service,
which is shared between all users, and it may be more convenient to use
configuration files to modify settings, see systemd-user.conf(5), or a
drop-in that specifies one of the environment variables listed above in
"Environment, see systemd.unit(5).
--unit=
Set default unit to activate on startup. If not specified, defaults
to default.target. See systemd.unit= above.
--dump-core
Enable core dumping on crash. This switch has no effect when
running as user instance. Same as systemd.dump_core= above.
--crash-vt=VT
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!).
--crash-shell
Run a shell on crash. This switch has no effect when running as
user instance. See systemd.crash_shell= above.
--crash-reboot
Automatically reboot the system on crash. This switch has no effect
when running as user instance. See systemd.crash_reboot above.
--confirm-spawn
Ask for confirmation when spawning processes. This switch has no
effect when run as user instance. See systemd.confirm_spawn above.
--show-status
Show terse unit status information is shown on the console during
boot-up and shutdown. See systemd.show_status above.
--log-target=
Set log target. See systemd.log_target above.
--log-level=
Set log level. See systemd.log_level above.
--log-color
Highlight important log messages. See systemd.log_color above.
--log-location
Include code location in log messages. See systemd.log_location
above.
--machine-id=
Override the machine-id set on the hard drive. See
systemd.machine_id= above.
--service-watchdogs
Globally enable/disable all service watchdog timeouts and emergency
actions. See systemd.service_watchdogs above.
--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.
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/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[11], 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/cgroup-v1/cgroups.txt
2. Original Design Document
http://0pointer.de/blog/projects/systemd.html
3. Interface Stability Promise
https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise
4. Container Interface
https://systemd.io/CONTAINER_INTERFACE
5. initrd Interface
https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface
6. XDG Base Directory specification
http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
7. Known Environment Variables
https://systemd.io/ENVIRONMENT
8. 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.
9. unified cgroup hierarchy
https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html
10. legacy cgroup hierarchy
https://www.kernel.org/doc/Documentation/cgroup-v1/
11. systemd Homepage
https://www.freedesktop.org/wiki/Software/systemd/
systemd 245 SYSTEMD(1)