Provided by: systemd_253.5-1ubuntu6.1_amd64 bug

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/