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.
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 cgroups.txt[1] for more information about control
groups, or short "cgroups"). systemd uses this to effectively keep
track of processes. Control group information is maintained in the kernel,
and is accessible via the file system hierarchy (beneath
/sys/fs/cgroup/systemd/), or in tools such as systemd-cgls(1) or
ps(1) (ps xawf -eo pid,user,cgroup,args is particularly useful
to list all processes and the systemd units they belong to.).
systemd is compatible with the SysV init system to a large degree:
SysV init scripts are supported and simply read as an alternative (though
limited) configuration file format. The SysV /dev/initctl interface is
provided, and compatibility implementations of the various SysV client tools
are available. In addition to that, various established Unix functionality
such as /etc/fstab or the utmp database are supported.
systemd has a minimal transaction system: if a unit is requested
to start up or shut down it will add it and all its dependencies to a
temporary transaction. Then, it will verify if the transaction is consistent
(i.e. whether the ordering of all units is cycle-free). If it is not,
systemd will try to fix it up, and removes non-essential jobs from the
transaction that might remove the loop. Also, systemd tries to suppress
non-essential jobs in the transaction that would stop a running service.
Finally it is checked whether the jobs of the transaction contradict jobs
that have already been queued, and optionally the transaction is aborted
then. If all worked out and the transaction is consistent and minimized in
its impact it is merged with all already outstanding jobs and added to the
run queue. Effectively this means that before executing a requested
operation, systemd will verify that it makes sense, fixing it if possible,
and only failing if it really cannot work.
Note that transactions are generated independently of a unit's
state at runtime, hence, for example, if a start job is requested on an
already started unit, it will still generate a transaction and wake up any
inactive dependencies (and cause propagation of other jobs as per the
defined relationships). This is because the enqueued job is at the time of
execution compared to the target unit's state and is marked successful and
complete when both satisfy. However, this job also pulls in other
dependencies due to the defined relationships and thus leads to, in our
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 initial RAM disk (initrd), while
the one that is not prefixed only in the main system.
systemd.dump_core
Takes a boolean argument or enables the option if
specified without an argument. If enabled, the systemd manager (PID 1) dumps
core when it crashes. Otherwise, no core dump is created. Defaults to
enabled.
systemd.crash_chvt
Takes a positive integer, or a boolean argument. Can be
also specified without an argument, with the same effect as a positive
boolean. If a positive integer (in the range 1–63) is specified, the
system manager (PID 1) will activate the specified virtual terminal 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.unified_cgroup_hierarchy
When specified without an argument or with a true
argument, enables the usage of
unified cgroup hierarchy[8]
(a.k.a. cgroups-v2). When specified with a false argument, fall back to
hybrid or full legacy cgroup hierarchy.
If this option is not specified, the default behaviour is
determined during compilation (the -Ddefault-hierarchy= meson
option). If the kernel does not support unified cgroup hierarchy, the legacy
hierarchy will be used even if this option is specified.
systemd.legacy_systemd_cgroup_controller
Takes effect if the full unified cgroup hierarchy is not
used (see previous option). When specified without an argument or with a true
argument, disables the use of "hybrid" cgroup hierarchy (i.e. a
cgroups-v2 tree used for systemd, and
legacy cgroup hierarchy[9],
a.k.a. cgroups-v1, for other controllers), and forces a full
"legacy" mode. When specified with a false argument, enables the use
of "hybrid" hierarchy.
If this option is not specified, the default behaviour is
determined during compilation (the -Ddefault-hierarchy= meson
option). If the kernel does not support unified cgroup hierarchy, the legacy
hierarchy will be used even if this option is specified.
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[10] documentation.
systemd.import_credentials=
Takes a boolean argument. If false disables importing
credentials from the kernel command line, qemu_fw_cfg subsystem or the kernel
command line.
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.
SEE ALSO¶
The systemd Homepage[11], systemd-system.conf(5),
locale.conf(5), systemctl(1), journalctl(1),
systemd-notify(1), daemon(7), sd-daemon(3),
org.freedesktop.systemd1(5), systemd.unit(5),
systemd.special(7), pkg-config(1),
kernel-command-line(7), bootup(7),
systemd.directives(7)
NOTES¶
- 1.
- cgroups.txt
- 2.
- Original Design Document
- 3.
- Interface Portability and Stability Promise
- 4.
- Container Interface
- 5.
- initrd Interface
- 6.
- XDG Base Directory specification
- 7.
- Known Environment Variables
- 8.
- unified cgroup hierarchy
- 9.
- legacy cgroup hierarchy
- 10.
- System and Service Credentials
- 11.
- systemd Homepage