| SYSTEMD(1) | systemd | SYSTEMD(1) |
.SH "NAME" systemd, init - systemd system and service manager
.SH "SYNOPSIS"
.HP 600u
/usr/lib/systemd/systemd
[OPTIONS...]
.HP 120u
init
[OPTIONS...]
.SH "DESCRIPTION"
.PP 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.
.PP 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.
.PP 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.
.PP 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/, /proc/, and /dev/.
.PP systemd will also reset the system clock during early boot if it
appears to be set incorrectly. See "System clock epoch" section
below.
.PP Note that some but not all interfaces provided by systemd are covered by
the Interface Portability and Stability Promise[1].
.PP The D-Bus API of systemd is described in
org.freedesktop.systemd1(5) and
org.freedesktop.LogControl1(5).
.PP Systems which invoke systemd in a container or initrd environment should
implement the Container Interface[2] or initrd Interface[3]
specifications, respectively.
.SH "UNITS"
.PP 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 in a number of states,
described in the following table. Note that the various unit types may have
a number of additional substates, which are mapped to the generalized unit
states described here.
.sp
Table 1. Unit ACTIVE states
| State | Description |
| active | Started, bound, plugged in, ..., depending on the unit type. |
| inactive | Stopped, unbound, unplugged, ..., depending on the unit type. |
| failed | Similar to inactive, but the unit failed in some way (process returned error code on exit, crashed, an operation timed out, or after too many restarts). |
| activating | Changing from inactive to active. |
| deactivating | Changing from active to inactive. |
| maintenance | Unit is inactive and a maintenance operation is in progress. |
| reloading | Unit is active and it is reloading its configuration. |
| refreshing | Unit is active and a new mount is being activated in its namespace. |
.PP The following unit types are available:
.PP Units are named as their configuration files. Some units have special
semantics. A detailed list is available in systemd.special(7).
.PP 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.
.PP 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.
.PP 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.
.PP 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).
.PP 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:
.PP 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.
.PP 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[4] 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.).
.PP systemd is compatible with various established Unix functionality such as
/etc/fstab or the utmp database.
.PP 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.
.PP 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.
.PP 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).
.SH "DIRECTORIES"
.PP 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).
.RE
.PP User unit directories
Similar rules apply for the user unit directories. However, here the XDG
Base Directory specification[5] 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).
.RE
.SH "SIGNALS"
.PP 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.
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP SIGPWR
When this signal is received the systemd manager will start the sigpwr.target
unit. This is mostly equivalent to systemctl start sigpwr.target.
.RE
.PP SIGUSR1
When this signal is received the systemd manager will try to reconnect to the
D-Bus bus.
.RE
.PP 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.
.RE
.PP SIGHUP
Reloads the complete daemon configuration. This is mostly equivalent to
systemctl daemon-reload.
.RE
.PP SIGRTMIN+0
Enters default mode, starts the default.target unit. This is mostly
equivalent to systemctl isolate default.target.
.RE
.PP SIGRTMIN+1
Enters rescue mode, starts the rescue.target unit. This is mostly equivalent
to systemctl isolate rescue.target.
.RE
.PP SIGRTMIN+2
Enters emergency mode, starts the emergency.service unit. This is mostly
equivalent to systemctl isolate emergency.service.
.RE
.PP SIGRTMIN+3
Halts the machine, starts the halt.target unit. This is mostly equivalent to
systemctl start halt.target --job-mode=replace-irreversibly.
.RE
.PP SIGRTMIN+4
Powers off the machine, starts the poweroff.target unit. This is mostly
equivalent to systemctl start poweroff.target
--job-mode=replace-irreversibly.
.RE
.PP SIGRTMIN+5
Reboots the machine, starts the reboot.target unit. This is mostly equivalent
to systemctl start reboot.target --job-mode=replace-irreversibly.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP SIGRTMIN+13
Immediately halts the machine.
.RE
.PP SIGRTMIN+14
Immediately powers off the machine.
.RE
.PP SIGRTMIN+15
Immediately reboots the machine.
.RE
.PP SIGRTMIN+16
Immediately reboots the machine with kexec.
.RE
.PP SIGRTMIN+17
Immediately reboots the userspace.
Added in version 254.
.RE
.PP SIGRTMIN+20
Enables display of status messages on the console, as controlled via
systemd.show_status=1 on the kernel command line.
You may want to use SetShowStatus() instead of SIGRTMIN+20 in
order to prevent race conditions. See
org.freedesktop.systemd1(5).
.RE
.PP SIGRTMIN+21
Disables display of status messages on the console, as controlled via
systemd.show_status=0 on the kernel command line.
You may want to use SetShowStatus() instead of SIGRTMIN+21 in
order to prevent race conditions. See
org.freedesktop.systemd1(5).
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP SIGRTMIN+24
Immediately exits the manager (only available for --user instances).
Added in version 195.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.SH "ENVIRONMENT"
.PP 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).
.PP Some of the variables understood by systemd:
.PP $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=.
.RE
.PP $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=.
.RE
.PP $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.
.RE
.PP $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=.
.RE
.PP $SYSTEMD_LOG_TID
A boolean. If true, messages will be prefixed with the current numerical
thread ID (TID).
Added in version 247.
.RE
.PP $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=.
.RE
.PP $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.
.RE
.PP $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[5] to find its configuration.
.RE
.PP $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.
.RE
.PP $SYSTEMD_PAGER, $PAGER
Pager to use when --no-pager is not given. $SYSTEMD_PAGER is
used if set; otherwise $PAGER is used. If neither
$SYSTEMD_PAGER nor $PAGER are set, a set of well-known pager
implementations is tried in turn, including less(1) and
more(1), until one is found. If no pager implementation is
discovered, no pager is invoked. Setting those environment variables to an
empty string or the value cat is equivalent to passing
--no-pager.
Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER and
$PAGER can only be used to disable the pager (with cat or ), and are
otherwise ignored.
.RE
.PP $SYSTEMD_LESS
Override the options passed to less (by default FRSXMK).
Users might want to change two options in particular:
.PP 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.
.RE
.PP 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.
.RE
.sp
Note that setting the regular $LESS environment variable has no effect
for less invocations by systemd tools.
See less(1) for more discussion.
.RE
.PP $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.
.RE
.PP $SYSTEMD_PAGERSECURE
Common pager commands like less(1), in addition to "paging",
i.e. scrolling through the output, support opening of or writing to other
files and running arbitrary shell commands. When commands are invoked with
elevated privileges, for example under sudo(8) or pkexec(1),
the pager becomes a security boundary. Care must be taken that only programs
with strictly limited functionality are used as pagers, and unintended
interactive features like opening or creation of new files or starting of
subprocesses are not allowed. "Secure mode" for the pager may be
enabled as described below, if the pager supports that (most pagers
are not written in a way that takes this into consideration). It is
recommended to either explicitly enable "secure mode" or to
completely disable the pager using --no-pager or PAGER=cat
when allowing untrusted users to execute commands with elevated
privileges.
This option takes a boolean argument. When set to true, the "secure
mode" of the pager is enabled. In "secure mode",
LESSSECURE=1 will be set when invoking the pager, which instructs the
pager to disable commands that open or create new files or start new
subprocesses. Currently only less(1) is known to understand this
variable and implement "secure mode".
When set to false, no limitation is placed on the pager. Setting
SYSTEMD_PAGERSECURE=0 or not removing it from the inherited
environment may allow the user to invoke arbitrary commands.
When $SYSTEMD_PAGERSECURE is not set, systemd tools attempt to
automatically figure out if "secure mode" should be enabled and
whether the pager supports it. "Secure mode" is enabled if the
effective UID is not the same as the owner of the login session, see
geteuid(2) and sd_pid_get_owner_uid(3), or when running under
sudo(8) or similar tools ($SUDO_UID is set [6]). In those
cases, SYSTEMD_PAGERSECURE=1 will be set and pagers which are not
known to implement "secure mode" will not be used at all. Note
that this autodetection only covers the most common mechanisms to elevate
privileges and is intended as convenience. It is recommended to explicitly
set $SYSTEMD_PAGERSECURE or disable the pager.
Note that if the $SYSTEMD_PAGER or $PAGER variables are to be
honoured, other than to disable the pager, $SYSTEMD_PAGERSECURE must
be set too.
.RE
.PP $SYSTEMD_COLORS
Takes a boolean argument, or a special value. By default (unset),
systemd and related utilities will use colors in their output if
possible. If $COLORTERM is set to truecolor or 24bit, 24-bit colors
will be enabled, 256 colors otherwise, unless $NO_COLOR or
$TERM indicates colors are disabled.
.PP true
Same as unset, except that $NO_COLOR is ignored.
.RE
.PP false
The output will be monochrome.
.RE
.PP 16, 256, 24bit
Always use the base 16 ANSI colors, 256 colors, or 24 bit color,
respectively.
.RE
.PP auto-16, auto-256, auto-24bit
Use the given quantity of colours, subject to $TERM, and what the
console is connected to.
.RE
.sp
.RE
.PP $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.
.RE
.PP $LISTEN_PID, $LISTEN_PIDFDID, $LISTEN_FDS,
$LISTEN_FDNAMES
Set by systemd for supervised processes during socket-based activation. See
sd_listen_fds(3) for more information.
.RE
.PP $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.
.RE
.PP For further environment variables understood by systemd and its various
components, see Known Environment Variables[7].
.SH "KERNEL COMMAND LINE"
.PP 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
instead.
.PP The following variables are understood:
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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. Otherwise, no shell is spawned. Defaults to disabled, for security
reasons, as the shell is not protected by password authentication.
Added in version 233.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP systemd.credentials_boot_policy=
Controls under which conditions a credential encrypted with a null key (i.e.
a credential wrapped in a systemd-creds envelope but offering neither
confidentiality nor authenticity, see systemd-creds(1)) is accepted
at boot. This provides a fallback for provisioning credentials before a
machine has a key to encrypt them against, for example during first boot or
on systems without a TPM2 device. Takes one of strict, tofu,
relaxed or off:
.sp
Defaults to relaxed. Note that this policy only applies to the default
acceptance decision; it has no effect on credentials encrypted against a
host key or TPM2 device, which are always accepted.
For further information see System and Service Credentials[8]
documentation.
Added in version 262.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP emergency, rd.emergency
Boot into emergency mode. Those options are equivalent to
systemd.unit=emergency.target or
rd.systemd.unit=emergency.target, respectively. They were initially
provided for compatibility with SysV, but are retained as convenient
shortcuts.
Added in version 186.
.RE
.PP rescue, rd.rescue, single, 1
Boot into rescue mode. Those options are equivalent to either
systemd.unit=rescue.target or rd.systemd.unit=rescue.target.
They were initially provided for compatibility with SysV, but are retained
as convenient shortcuts.
Added in version 186.
.RE
.PP 3, 5
Shortcuts to boot into specific targets: 3 is equivalent to
systemd.unit=multi-user.target and 5 is equivalent to
systemd.unit=graphical.target. Those options were initially provided
for compatibility with SysV, but are retained as convenient shortcuts.
Added in version 186.
.RE
.PP 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.
.RE
.PP systemd.minimum_uptime_sec=
Takes a time in seconds. Specifies the minimum uptime of the system before
the system shuts down. For more information see the MinimumUptimeSec=
setting described in systemd-system.conf(5).
Added in version 261.
.RE
.PP For other kernel command line parameters understood by components of the
core OS, please refer to kernel-command-line(7).
.SH "SYSTEM CREDENTIALS"
.PP 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:
.PP Invoke systemd-creds(1) as follows to see the list of credentials
passed into the system:
# systemd-creds --system list
.PP For further information see System and Service Credentials[8]
documentation.
.PP The service manager when run as PID 1 consumes the following system
credentials:
.PP 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.
.RE
.PP 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.
.RE
.PP For a list of system credentials various other components of systemd
consume, see systemd.system-credentials(7).
.SH "READINESS PROTOCOL"
.PP 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).
.PP 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.
.PP 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:
Added in version 256.
Added in version 256.
.sp
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 that indicates 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.
Added in version 256.
Added in version 256.
Added in version 256.
.PP Note that these extension fields are sent in addition to the regular
READY=1 and RELOADING=1 notifications.
.SH "OPTIONS"
.PP 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.
.SS "Introspection and debugging options"
.PP Those options are used for testing and introspection, and systemd
may be invoked with them at any time:
.PP --dump-configuration-items
Dump understood unit configuration items. This outputs a terse but complete
list of configuration items understood in unit definition files.
.RE
.PP --dump-bus-properties
Dump exposed bus properties. This outputs a terse but complete list of
properties exposed on D-Bus.
Added in version 239.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP -h, --help
Print a short help text and exit.
.RE
.PP --version
Print a short version string and exit.
.RE
.SS "Options that duplicate kernel command line settings"
.PP 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.
.PP 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.
.PP --unit=
Set default unit to activate on startup. If not specified, defaults to
default.target. See systemd.unit= above.
.RE
.PP --dump-core
Enable core dumping on crash. This switch has no effect when running as user
instance. Same as systemd.dump_core= above.
.RE
.PP --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.
.RE
.PP --crash-shell
Run a shell on crash. This switch has no effect when running as user
instance. See systemd.crash_shell= above.
.RE
.PP --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.
.RE
.PP --confirm-spawn
Ask for confirmation when spawning processes. This switch has no effect when
run as user instance. See systemd.confirm_spawn above.
.RE
.PP --show-status
Show terse unit status information on the console during boot-up and
shutdown. See systemd.show_status above.
Added in version 244.
.RE
.PP --log-color
Highlight important log messages. See systemd.log_color above.
Added in version 244.
.RE
.PP --log-level=
Set log level. See systemd.log_level above.
.RE
.PP --log-location
Include code location in log messages. See systemd.log_location
above.
Added in version 244.
.RE
.PP --log-target=
Set log target. See systemd.log_target above.
.RE
.PP --log-time=
Prefix console messages with timestamp. See systemd.log_time
above.
Added in version 246.
.RE
.PP --machine-id=
Override the machine-id set on the hard drive. See systemd.machine_id=
above.
Added in version 229.
.RE
.PP --service-watchdogs
Globally enable/disable all service watchdog timeouts and emergency actions.
See systemd.service_watchdogs above.
Added in version 237.
.RE
.PP --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.
.RE
.SH "SYSTEM CLOCK EPOCH"
.PP When systemd is started or restarted, it may set the system clock
to the "epoch". This mechanism is used to ensure that the system
clock remains somewhat reasonably initialized and roughly monotonic across
reboots, in case no battery-backed local RTC is available or it does not
work correctly.
.PP The epoch is the lowest date above which the system clock time is assumed
to be set correctly. When initializing, the local clock is advanced
to the epoch if it was set to a lower value. As a special case, if the local
clock is sufficiently far in the future (by default 15 years, but this can
be configured at build time), the hardware clock is assumed to be broken,
and the system clock is rewound to the epoch.
.PP The epoch is set to the highest of: the build time of systemd, the
modification time ("mtime") of /usr/lib/clock-epoch, and the
modification time of /var/lib/systemd/timesync/clock.
.SH "FILES"
.PP /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).
.RE
.PP /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.
.RE
.PP /usr/lib/clock-epoch
The modification time ("mtime") of this file is used for the time
epoch, see previous section.
Added in version 247.
.RE
.PP /var/lib/systemd/timesync/clock
The modification time ("mtime") of this file is updated by
systemd-timesyncd.service(8). If present, the modification time of
file is used for the epoch, see previous section.
Added in version 257.
.RE
.SH "HISTORY"
.PP 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.
.RE
.SH "SEE ALSO"
.PP 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), org.freedesktop.systemd1(5)
.PP For more information about the concepts and ideas behind systemd, please
refer to the Original Design Document[10].
NOTES
- 1.
- Interface Portability and Stability Promise
- 2.
- Container Interface
- 3.
- initrd Interface
- 4.
- Control Groups v2
- 5.
- XDG Base Directory specification
- 6.
-
It is recommended for other tools to set and check $SUDO_UID as appropriate, treating it is a common interface. - 7.
- Known Environment Variables
- 8.
- System and Service Credentials
- 9.
- systemd Homepage
- 10.
- Original Design Document
| systemd 262.2 |