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 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.
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+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.
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
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 user@.service. Additional entries may be configured
(as for any other service) through the Environment= and EnvironmentFile=
settings for user@.service (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). 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.
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=.
$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).
$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=.
$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.
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_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 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
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.
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.
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.
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 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).
systemd.log_color, systemd.log_level=, systemd.log_location,
systemd.log_target=, systemd.log_time, systemd.log_tid
Controls log output, with the same effect as the $SYSTEMD_LOG_COLOR,
$SYSTEMD_LOG_LEVEL, $SYSTEMD_LOG_LOCATION, $SYSTEMD_LOG_TARGET,
$SYSTEMD_LOG_TIME, and $SYSTEMD_LOG_TID environment variables
described above. systemd.log_color, systemd.log_location,
systemd.log_time, and systemd.log_tid= 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.set_credential=
Sets a system credential, which can then be propagated to system
services using the LoadCredential= setting, see systemd.exec(5) for
details. Takes a pair of credential name and value, separated by a
colon. 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.
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.
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 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
user@.service(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!).
--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 on the console during boot-up and
shutdown. See systemd.show_status above.
--log-color
Highlight important log messages. See systemd.log_color above.
--log-level=
Set log level. See systemd.log_level above.
--log-location
Include code location in log messages. See systemd.log_location
above.
--log-target=
Set log target. See systemd.log_target above.
--log-time=
Prefix console messages with timestamp. See systemd.log_time 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.
HISTORY
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.
SEE ALSO
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)
NOTES
1. Control Groups v2
https://docs.kernel.org/admin‐guide/cgroup‐v2.html
2. Original Design Document
http://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/
systemd 253 SYSTEMD(1)