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NAME | SYNOPSIS | DESCRIPTION | CONCEPTS | DIRECTORIES | SIGNALS | ENVIRONMENT | KERNEL COMMAND LINE | SYSTEM CREDENTIALS | READINESS PROTOCOL | OPTIONS | SOCKETS AND FIFOS | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD(1) systemd SYSTEMD(1)
systemd, init - systemd system and service manager
/usr/lib/systemd/systemd [OPTIONS...]
init [OPTIONS...] {COMMAND}
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 [email protected](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.
systemd provides a dependency system between various entities
called "units" of 11 different types. Units encapsulate various
objects that are relevant for system boot-up and maintenance. The
majority of units are configured in unit configuration files,
whose syntax and basic set of options is described in
systemd.unit(5), however some are created automatically from
other configuration files, dynamically from system state or
programmatically at runtime. Units may be "active" (meaning
started, bound, plugged in, ..., depending on the unit type, see
below), or "inactive" (meaning stopped, unbound, unplugged, ...),
as well as in the process of being activated or deactivated, i.e.
between the two states (these states are called "activating",
"deactivating"). A special "failed" state is available as well,
which is very similar to "inactive" and is entered when the
service failed in some way (process returned error code on exit,
or crashed, an operation timed out, or after too many restarts).
If this state is entered, the cause will be logged, for later
reference. Note that the various unit types may have a number of
additional substates, which are mapped to the five generalized
unit states described here.
The following unit types are available:
1. Service units, which start and control daemons and the
processes they consist of. For details, see
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.
On first boot, systemd will enable or disable units according to
preset policy. See systemd.preset(5) and "First Boot Semantics"
in machine-id(5).
systemd only keeps a minimal set of units loaded into memory.
Specifically, the only units that are kept loaded into memory are
those for which at least one of the following conditions is true:
1. It is in an active, activating, deactivating or failed state
(i.e. in any unit state except for "inactive")
2. It has a job queued for it
3. It is a dependency of at least one other unit that is loaded
into memory
4. It has some form of resource still allocated (e.g. a service
unit that is inactive but for which a process is still
lingering that ignored the request to be terminated)
5. It has been pinned into memory programmatically by a D-Bus
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 Control Groups v2[1] for more information
about control groups, or short "cgroups"). systemd uses this to
effectively keep track of processes. Control group information is
maintained in the kernel, and is accessible via the file system
hierarchy (beneath /sys/fs/cgroup/), or in tools such as
systemd-cgls(1) or ps(1) (ps xawf -eo pid,user,cgroup,args is
particularly useful to list all processes and the systemd units
they belong to.).
systemd is compatible with the SysV init system to a large
degree: SysV init scripts are supported and simply read as an
alternative (though limited) configuration file format. The SysV
/dev/initctl interface is provided, and compatibility
implementations of the various SysV client tools are available.
In addition to that, various established Unix functionality such
as /etc/fstab or the utmp database are supported.
systemd has a minimal transaction system: if a unit is requested
to start up or shut down it will add it and all its dependencies
to a temporary transaction. Then, it will verify if the
transaction is consistent (i.e. whether the ordering of all units
is cycle-free). If it is not, systemd will try to fix it up, and
removes non-essential jobs from the transaction that might remove
the loop. Also, systemd tries to suppress non-essential jobs in
the transaction that would stop a running service. Finally it is
checked whether the jobs of the transaction contradict jobs that
have already been queued, and optionally the transaction is
aborted then. If all worked out and the transaction is consistent
and minimized in its impact it is merged with all already
outstanding jobs and added to the run queue. Effectively this
means that before executing a requested operation, systemd will
verify that it makes sense, fixing it if possible, and only
failing if it really cannot work.
Note that transactions are generated independently of a unit's
state at runtime, hence, for example, if a start job is requested
on an already started unit, it will still generate a transaction
and wake up any inactive dependencies (and cause propagation of
other jobs as per the defined relationships). This is because the
enqueued job is at the time of execution compared to the target
unit's state and is marked successful and complete when both
satisfy. However, this job also pulls in other dependencies due
to the defined relationships and thus leads to, in our example,
start jobs for any of those inactive units getting queued as
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 Portability and Stability Promise[3].
Units may be generated dynamically at boot and system manager
reload time, for example based on other configuration files or
parameters passed on the kernel command line. For details, see
systemd.generator(7).
The D-Bus API of systemd is described in
org.freedesktop.systemd1(5) and org.freedesktop.LogControl1(5).
Systems which invoke systemd in a container or initrd environment
should implement the Container Interface[4] or initrd
Interface[5] specifications, respectively.
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.
The service listens to various UNIX process signals that can be
used to request various actions asynchronously. The signal
handling is enabled very early during boot, before any further
processes are invoked. However, a supervising container manager
or similar that intends to request these operations via this
mechanism must take into consideration that this functionality is
not available during the earliest initialization phase. An
sd_notify() notification message carrying the
X_SYSTEMD_SIGNALS_LEVEL=2 field is emitted once the signal
handlers are enabled, see below. This may be used to schedule
submission of these signals correctly.
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+7
Reboots userspace, starts the soft-reboot.target unit. This
is mostly equivalent to systemctl start soft-reboot.target
--job-mode=replace-irreversibly.
Added in version 254.
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+17
Immediately reboots the userspace.
Added in version 254.
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".
Added in version 239.
SIGRTMIN+24
Immediately exits the manager (only available for --user
instances).
Added in version 195.
SIGRTMIN+25
Upon receiving this signal the systemd manager will reexecute
itself. This is mostly equivalent to systemctl daemon-reexec
except that it will be done asynchronously.
The systemd system manager treats this signal the same way as
SIGTERM.
Added in version 250.
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.
Added in version 239.
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.
Added in version 239.
The environment block for the system manager is initially set by
the kernel. (In particular, "key=value" assignments on the kernel
command line are turned into environment variables for PID 1).
For the user manager, the system manager sets the environment as
described in the "Environment Variables in Spawned Processes"
section of systemd.exec(5). The DefaultEnvironment= setting in
the system manager applies to all services including
[email protected]. Additional entries may be configured (as for any
other service) through the Environment= and EnvironmentFile=
settings for [email protected] (see systemd.exec(5)). Also,
additional environment variables may be set through the
ManagerEnvironment= setting in systemd-system.conf(5) and
systemd-user.conf(5).
Some of the variables understood by systemd:
$SYSTEMD_LOG_LEVEL
The maximum log level of emitted messages (messages with a
higher log level, i.e. less important ones, will be
suppressed). Takes a comma-separated list of values. A value
may be either one of (in order of decreasing importance)
emerg, alert, crit, err, warning, notice, info, debug, or an
integer in the range 0...7. See syslog(3) for more
information. Each value may optionally be prefixed with one
of console, syslog, kmsg or journal followed by a colon to
set the maximum log level for that specific log target (e.g.
SYSTEMD_LOG_LEVEL=debug,console:info specifies to log at
debug level except when logging to the console which should
be at info level). Note that the global maximum log level
takes priority over any per target maximum log levels.
This can be overridden with --log-level=.
$SYSTEMD_LOG_COLOR
A boolean. If true, messages written to the tty will be
colored according to priority.
This can be overridden with --log-color=.
$SYSTEMD_LOG_TIME
A boolean. If true, console log messages will be prefixed
with a timestamp.
This can be overridden with --log-time=.
Added in version 246.
$SYSTEMD_LOG_LOCATION
A boolean. If true, messages will be prefixed with a filename
and line number in the source code where the message
originates.
This can be overridden with --log-location=.
$SYSTEMD_LOG_TID
A boolean. If true, messages will be prefixed with the
current numerical thread ID (TID).
Added in version 247.
$SYSTEMD_LOG_TARGET
The destination for log messages. One of console (log to the
attached tty), console-prefixed (log to the attached tty but
with prefixes encoding the log level and "facility", see
syslog(3), kmsg (log to the kernel circular log buffer),
journal (log to the journal), journal-or-kmsg (log to the
journal if available, and to kmsg otherwise), auto (determine
the appropriate log target automatically, the default), null
(disable log output).
This can be overridden with --log-target=.
$SYSTEMD_LOG_RATELIMIT_KMSG
Whether to ratelimit kmsg or not. Takes a boolean. Defaults
to "true". If disabled, systemd will not ratelimit messages
written to kmsg.
Added in version 254.
$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, $SYSTEMD_GENERATOR_PATH,
$SYSTEMD_ENVIRONMENT_GENERATOR_PATH
Controls where systemd looks for unit files and generators.
These variables may contain a list of paths, separated by
colons (":"). When set, if the list ends with an empty
component ("...:"), this list is prepended to the usual set
of paths. Otherwise, the specified list replaces the usual
set of paths.
$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.
Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER (as
well as $PAGER) will be silently ignored.
$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.
Note that setting the regular $LESS environment variable has
no effect for less invocations by systemd tools.
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).
Note that setting the regular $LESSCHARSET environment
variable has no effect for less invocations by systemd tools.
$SYSTEMD_PAGERSECURE
Takes a boolean argument. When true, the "secure" mode of the
pager is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE
is not set at all, secure mode is enabled if the effective
UID is not the same as the owner of the login session, see
geteuid(2) and sd_pid_get_owner_uid(3). In secure mode,
LESSSECURE=1 will be set when invoking the pager, and the
pager shall disable commands that open or create new files or
start new subprocesses. When $SYSTEMD_PAGERSECURE is not set
at all, pagers which are not known to implement secure mode
will not be used. (Currently only less(1) implements secure
mode.)
Note: when commands are invoked with elevated privileges, for
example under sudo(8) or pkexec(1), care must be taken to
ensure that unintended interactive features are not enabled.
"Secure" mode for the pager may be enabled automatically as
describe above. Setting SYSTEMD_PAGERSECURE=0 or not removing
it from the inherited environment allows the user to invoke
arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER
variables are to be honoured, $SYSTEMD_PAGERSECURE must be
set too. It might be reasonable to completely disable the
pager using --no-pager instead.
$SYSTEMD_COLORS
Takes a boolean argument. When true, systemd and related
utilities will use colors in their output, otherwise the
output will be monochrome. Additionally, the variable can
take one of the following special values: "16", "256" to
restrict the use of colors to the base 16 or 256 ANSI colors,
respectively. This can be specified to override the automatic
decision based on $TERM and what the console is connected to.
$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 service manager for its services for status and
readiness notifications. Also consumed by service manager for
notifying supervising container managers or service managers
up the stack about its own progress. See sd_notify(3) and the
relevant section below for more information.
For further environment variables understood by systemd and its
various components, see Known Environment Variables[7].
When run as the system instance, systemd parses a number of
options listed below. They can be specified as kernel command
line arguments which are parsed from a number of sources
depending on the environment in which systemd is executed. If run
inside a Linux container, these options are parsed from the
command line arguments passed to systemd itself, next to any of
the command line options listed in the Options section above. If
run outside of Linux containers, these arguments are parsed from
/proc/cmdline and from the "SystemdOptions" EFI variable (on EFI
systems) instead. Options from /proc/cmdline have higher
priority.
Note: use of "SystemdOptions" is deprecated.
The following variables are understood:
systemd.unit=, rd.systemd.unit=
Overrides the unit to activate on boot. Defaults to
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 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.
Added in version 233.
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 when it crashes. Defaults to
disabled, meaning that no such switch is attempted. If set to
enabled, the virtual terminal the kernel messages are written
to is used instead.
Added in version 233.
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.
Added in version 233.
systemd.crash_action=
Takes one of "freeze", "reboot" or "poweroff". Defaults to
"freeze". If set to "freeze", the system will hang
indefinitely when the system manager (PID 1) crashes. If set
to "reboot", the system manager (PID 1) will reboot the
machine automatically when it crashes, after a 10s delay. If
set to "poweroff", the system manager (PID 1) will power off
the machine immediately when it crashes. If combined with
systemd.crash_shell, the configured crash action is executed
after the shell exits.
Added in version 256.
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.
Added in version 233.
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.
Added in version 237.
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).
Added in version 233.
systemd.status_unit_format=
Takes name, description or combined as the value. If name,
the system manager will use unit names in status messages. If
combined, the system manager will use unit names and
description in status messages. When specified, overrides the
system manager configuration file option StatusUnitFormat=,
see systemd-system.conf(5).
Added in version 243.
systemd.log_color, systemd.log_level=, systemd.log_location,
systemd.log_target=, systemd.log_time, systemd.log_tid,
systemd.log_ratelimit_kmsg
Controls log output, with the same effect as the
$SYSTEMD_LOG_COLOR, $SYSTEMD_LOG_LEVEL,
$SYSTEMD_LOG_LOCATION, $SYSTEMD_LOG_TARGET,
$SYSTEMD_LOG_TIME, $SYSTEMD_LOG_TID and
$SYSTEMD_LOG_RATELIMIT_KMSG environment variables described
above. systemd.log_color, systemd.log_location,
systemd.log_time, systemd.log_tid and
systemd.log_ratelimit_kmsg can be specified without an
argument, with the same effect as a positive boolean.
systemd.default_standard_output=, systemd.default_standard_error=
Controls default standard output and error output for
services and sockets. That is, controls the default for
StandardOutput= and StandardError= (see systemd.exec(5) for
details). Takes one of inherit, null, tty, journal,
journal+console, kmsg, kmsg+console. If the argument is
omitted systemd.default-standard-output= defaults to journal
and systemd.default-standard-error= to inherit.
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.
Added in version 229.
systemd.set_credential=, systemd.set_credential_binary=
Sets a system credential, which can then be propagated to
system services using the ImportCredential= or
LoadCredential= setting, see systemd.exec(5) for details.
Takes a pair of credential name and value, separated by a
colon. The systemd.set_credential= parameter expects the
credential value in literal text form, the
systemd.set_credential_binary= parameter takes binary data
encoded in Base64. Note that the kernel command line is
typically accessible by unprivileged programs in
/proc/cmdline. Thus, this mechanism is not suitable for
transferring sensitive data. Use it only for data that is not
sensitive (e.g. public keys/certificates, rather than private
keys), or in testing/debugging environments.
For further information see System and Service Credentials[8]
documentation.
Added in version 251.
systemd.import_credentials=
Takes a boolean argument. If false disables importing
credentials from the kernel command line, the DMI/SMBIOS OEM
string table, the qemu_fw_cfg subsystem or the EFI kernel
stub.
Added in version 251.
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.
Added in version 186.
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.
Added in version 205.
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.
Added in version 186.
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.
Added in version 186.
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.
Added in version 186.
locale.LANG=, locale.LANGUAGE=, locale.LC_CTYPE=,
locale.LC_NUMERIC=, locale.LC_TIME=, locale.LC_COLLATE=,
locale.LC_MONETARY=, locale.LC_MESSAGES=, locale.LC_PAPER=,
locale.LC_NAME=, locale.LC_ADDRESS=, locale.LC_TELEPHONE=,
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).
Added in version 186.
For other kernel command line parameters understood by components
of the core OS, please refer to kernel-command-line(7).
During initialization the service manager will import credentials
from various sources into the system's set of credentials, which
can then be propagated into services and consumed by generators:
• When the service manager first initializes it will read
system credentials from SMBIOS Type 11 vendor strings
io.systemd.credential:name=value, and
io.systemd.credential.binary:name=value.
• At the same time it will import credentials from QEMU
"fw_cfg". (Note that the SMBIOS mechanism is generally
preferred, because it is faster and generic.)
• Credentials may be passed via the kernel command line, using
the systemd.set-credential= parameter, see above.
• Credentials may be passed from the UEFI environment via
systemd-stub(7).
• When the service manager is invoked during the initrd → host
transition it will import all files in
/run/credentials/@initrd/ as system credentials.
Invoke systemd-creds(1) as follows to see the list of credentials
passed into the system:
# systemd-creds --system list
For further information see System and Service Credentials[8]
documentation.
The service manager when run as PID 1 consumes the following
system credentials:
vmm.notify_socket
Contains a AF_VSOCK or AF_UNIX address where to send a
READY=1 notification message when the service manager has
completed booting. See sd_notify(3) and the next section for
more information. Note that in case the hypervisor does not
support SOCK_DGRAM over AF_VSOCK, SOCK_SEQPACKET will be
tried instead. The credential payload for AF_VSOCK should be
a string in the form "vsock:CID:PORT". "vsock-stream",
"vsock-dgram" and "vsock-seqpacket" can be used instead of
"vsock" to force usage of the corresponding socket type.
This feature is useful for machine managers or other
processes on the host to receive a notification via VSOCK
when a virtual machine has finished booting.
Added in version 254.
system.machine_id
Takes a 128bit hexadecimal ID to initialize /etc/machine-id
from, if the file is not set up yet. See machine-id(5) for
details.
Added in version 254.
For a list of system credentials various other components of
systemd consume, see systemd.system-credentials(7).
The service manager implements a readiness notification protocol
both between the manager and its services (i.e. down the stack),
and between the manager and a potential supervisor further up the
stack (the latter could be a machine or container manager, or in
case of a per-user service manager the system service manager
instance). The basic protocol (and the suggested API for it) is
described in sd_notify(3).
The notification socket the service manager (including PID 1)
uses for reporting readiness to its own supervisor is set via the
usual $NOTIFY_SOCKET environment variable (see above). Since this
is directly settable only for container managers and for the
per-user instance of the service manager, an additional mechanism
to configure this is available, in particular intended for use in
VM environments: the vmm.notify_socket system credential (see
above) may be set to a suitable socket (typically an AF_VSOCK
one) via SMBIOS Type 11 vendor strings. For details see above.
The notification protocol from the service manager up the stack
towards a supervisor supports a number of extension fields that
allow a supervisor to learn about specific properties of the
system and track its boot progress. Specifically the following
fields are sent:
• An X_SYSTEMD_HOSTNAME=... message will be sent out once the
initial hostname for the system has been determined. Note
that during later runtime the hostname might be changed again
programmatically, and (currently) no further notifications
are sent out in that case.
Added in version 256.
• An X_SYSTEMD_MACHINE_ID=... message will be sent out once
the machine ID of the system has been determined. See
machine-id(5) for details.
Added in version 256.
• An X_SYSTEMD_SIGNALS_LEVEL=... message will be sent out once
the service manager installed the various UNIX process signal
handlers described above. The field's value is an unsigned
integer formatted as decimal string, and indicates the
supported UNIX process signal feature level of the service
manager. Currently, only a single feature level is defined:
• X_SYSTEMD_SIGNALS_LEVEL=2 covers the various UNIX process
signals documented above – which are a superset of those
supported by the historical SysV init system.
Signals sent to PID 1 before this message is sent might not
be handled correctly yet. A consumer of these messages should
parse the value as an unsigned integer indication the level
of support. For now only the mentioned level 2 is defined,
but later on additional levels might be defined with higher
integers, that will implement a superset of the currently
defined behaviour.
Added in version 256.
• X_SYSTEMD_UNIT_ACTIVE=... and X_SYSTEMD_UNIT_INACTIVE=...
messages will be sent out for each target unit as it becomes
active or stops being active. This is useful to track boot
progress and functionality. For example, once the
ssh-access.target unit is reported started SSH access is
typically available, see systemd.special(7) for details.
Added in version 256.
• An X_SYSTEMD_SHUTDOWN=... message will be sent out very
shortly before the system shuts down. The value is one of the
strings "reboot", "halt", "poweroff", "kexec" and indicates
which kind of shutdown is being executed.
Added in version 256.
• An X_SYSTEMD_REBOOT_PARAMETER=... message will also be sent
out very shortly before the system shuts down. Its value is
the reboot argument as configured with systemctl
--reboot-argument=....
Added in version 256.
Note that these extension fields are sent in addition to the
regular "READY=1" and "RELOADING=1" notifications.
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.
Added in version 239.
--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 as a user manager, the kernel command line
is ignored and only the options described below are understood.
Nevertheless, systemd is usually started in this mode through the
[email protected](5) service, which is shared between all users. It
may be more convenient to use configuration files to modify
settings (see systemd-user.conf(5)), or environment variables.
See the "Environment" section above for a discussion of how the
environment block is set.
--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!).
Added in version 227.
--crash-shell
Run a shell on crash. This switch has no effect when running
as user instance. See systemd.crash_shell= above.
--crash-action=
Specify what to do when the system manager (PID 1) crashes.
This switch has no effect when systemd is running as user
instance. See systemd.crash_action= above.
Added in version 256.
--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 on the console during
boot-up and shutdown. See systemd.show_status above.
Added in version 244.
--log-color
Highlight important log messages. See systemd.log_color
above.
Added in version 244.
--log-level=
Set log level. See systemd.log_level above.
--log-location
Include code location in log messages. See
systemd.log_location above.
Added in version 244.
--log-target=
Set log target. See systemd.log_target above.
--log-time=
Prefix console messages with timestamp. See systemd.log_time
above.
Added in version 246.
--machine-id=
Override the machine-id set on the hard drive. See
systemd.machine_id= above.
Added in version 229.
--service-watchdogs
Globally enable/disable all service watchdog timeouts and
emergency actions. See systemd.service_watchdogs above.
Added in version 237.
--default-standard-output=, --default-standard-error=
Sets the default output or error output for all services and
sockets, respectively. See systemd.default_standard_output=
and systemd.default_standard_error= above.
/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.
systemd 252
Kernel command-line arguments
systemd.unified_cgroup_hierarchy and
systemd.legacy_systemd_cgroup_controller were deprecated.
Please switch to the unified cgroup hierarchy.
Added in version 252.
The systemd Homepage[9], systemd-system.conf(5), locale.conf(5),
systemctl(1), journalctl(1), systemd-notify(1), daemon(7),
sd-daemon(3), org.freedesktop.systemd1(5), systemd.unit(5),
systemd.special(7), pkg-config(1), kernel-command-line(7),
bootup(7), systemd.directives(7)
1. Control Groups v2
https://docs.kernel.org/admin-guide/cgroup-v2.html
2. Original Design Document
https://0pointer.de/blog/projects/systemd.html
3. Interface Portability and Stability Promise
https://systemd.io/PORTABILITY_AND_STABILITY/
4. Container Interface
https://systemd.io/CONTAINER_INTERFACE
5. initrd Interface
https://systemd.io/INITRD_INTERFACE/
6. XDG Base Directory specification
https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
7. Known Environment Variables
https://systemd.io/ENVIRONMENT
8. System and Service Credentials
https://systemd.io/CREDENTIALS
9. systemd Homepage
https://systemd.io/
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD(1)
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sd_journal_add_match(3), sd_journal_enumerate_fields(3), sd_journal_get_catalog(3), sd_journal_get_cursor(3), sd_journal_get_cutoff_realtime_usec(3), sd_journal_get_data(3), sd_journal_get_fd(3), sd_journal_get_realtime_usec(3), sd_journal_get_seqnum(3), sd_journal_get_usage(3), sd_journal_next(3), sd_journal_open(3), sd_journal_print(3), sd_journal_query_unique(3), sd_journal_seek_head(3), sd_journal_stream_fd(3), sd-json(3), sd_listen_fds(3), sd-login(3), sd_login_monitor_new(3), sd_machine_get_class(3), sd_notify(3), sd_pid_get_owner_uid(3), sd_seat_get_active(3), sd_session_is_active(3), sd_uid_get_state(3), sd_watchdog_enabled(3), ttyslot(3), udev_device_get_syspath(3), udev_device_has_tag(3), udev_device_new_from_syspath(3), udev_enumerate_add_match_subsystem(3), udev_enumerate_new(3), udev_enumerate_scan_devices(3), udev_list_entry(3), udev_monitor_filter_update(3), udev_monitor_new_from_netlink(3), udev_monitor_receive_device(3), udev_new(3), binfmt.d(5), [email protected](5), core(5), crypttab(5), dnf4.conf(5), dnssec-trust-anchors.d(5), environment.d(5), homed.conf(5), hostname(5), integritytab(5), journald.conf(5), journal-remote.conf(5), journal-upload.conf(5), locale.conf(5), localtime(5), logind.conf(5), machine-id(5), machine-info(5), modules-load.d(5), networkd.conf(5), oomd.conf(5), org.freedesktop.home1(5), org.freedesktop.hostname1(5), org.freedesktop.LogControl1(5), org.freedesktop.systemd1(5), os-release(5), pmlogger.control(5), proc(5), proc_sys_kernel(5), repart.d(5), resolved.conf(5), sysctl.d(5), systemd.automount(5), systemd.device(5), systemd.dnssd(5), systemd.exec(5), systemd.kill(5), systemd.mount(5), systemd.netdev(5), systemd.network(5), systemd.nspawn(5), systemd.path(5), systemd.pcrlock(5), systemd.preset(5), systemd.resource-control(5), systemd.scope(5), systemd.service(5), systemd-sleep.conf(5), systemd.slice(5), systemd.socket(5), systemd.swap(5), systemd-system.conf(5), systemd.target(5), systemd.timer(5), systemd.unit(5), sysupdate.d(5), sysusers.d(5), timesyncd.conf(5), tmpfiles.d(5), [email protected](5), utmp(5), vconsole.conf(5), veritytab(5), yum.conf(5), boot(7), bootparam(7), bootup(7), cgroups(7), daemon(7), file-hierarchy(7), kernel-command-line(7), mount_namespaces(7), pid_namespaces(7), smbios-type-11(7), systemd.directives(7), systemd.environment-generator(7), systemd.generator(7), systemd.image-policy(7), systemd.index(7), systemd.journal-fields(7), systemd.offline-updates(7), systemd.special(7), systemd.syntax(7), systemd.system-credentials(7), systemd.time(7), systemd.v(7), agetty(8), ctrlaltdel(8), logrotate(8), nss-myhostname(8), nss-mymachines(8), nss-resolve(8), nss-systemd(8), pam_systemd(8), pam_systemd_home(8), poweroff(8), runlevel(8), shutdown(8), systemd-ask-password-console.service(8), [email protected](8), systemd-battery-check.service(8), systemd-binfmt.service(8), systemd-bless-boot-generator(8), systemd-bless-boot.service(8), systemd-boot-check-no-failures.service(8), systemd-boot-random-seed.service(8), systemd-bsod.service(8), systemd-cryptsetup(8), systemd-cryptsetup-generator(8), systemd-debug-generator(8), systemd-environment-d-generator(8), [email protected](8), systemd-fstab-generator(8), systemd-getty-generator(8), systemd-gpt-auto-generator(8), systemd-hibernate-resume-generator(8), systemd-hibernate-resume.service(8), systemd-homed.service(8), systemd-hostnamed.service(8), systemd-importd.service(8), systemd-initctl.service(8), systemd-integritysetup-generator(8), [email protected](8), systemd-journald.service(8), systemd-journal-gatewayd.service(8), systemd-localed.service(8), systemd-logind.service(8), systemd-machined.service(8), systemd-machine-id-commit.service(8), [email protected](8), systemd-modules-load.service(8), systemd-mountfsd.service(8), systemd-networkd.service(8), systemd-networkd-wait-online.service(8), systemd-network-generator.service(8), systemd-nsresourced.service(8), systemd-oomd.service(8), systemd-pcrlock(8), systemd-pcrphase.service(8), systemd-portabled.service(8), systemd-poweroff.service(8), systemd-quotacheck.service(8), systemd-random-seed.service(8), systemd-rc-local-generator(8), systemd-remount-fs.service(8), systemd-repart(8), systemd-resolved.service(8), systemd-rfkill.service(8), systemd-run-generator(8), systemd-socket-proxyd(8), systemd-soft-reboot.service(8), systemd-ssh-generator(8), systemd-storagetm.service(8), systemd-suspend.service(8), systemd-sysctl.service(8), systemd-sysext(8), systemd-system-update-generator(8), systemd-sysupdate(8), systemd-sysusers(8), systemd-sysv-generator(8), systemd-timedated.service(8), systemd-timesyncd.service(8), systemd-time-wait-sync.service(8), systemd-tmpfiles(8), systemd-tpm2-generator(8), systemd-tpm2-setup.service(8), systemd-update-done.service(8), systemd-update-utmp.service(8), systemd-userdbd.service(8), systemd-user-sessions.service(8), systemd-vconsole-setup.service(8), systemd-veritysetup-generator(8), [email protected](8), systemd-volatile-root.service(8), systemd-xdg-autostart-generator(8), telinit(8), uuidd(8)
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