SYSTEMD(1) | systemd | SYSTEMD(1) |
NAME
systemd, init - systemd system and service managerSYNOPSIS
/usr/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. For compatibility with SysV, if systemd is called as init and a PID that 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.OPTIONS
The following options are understood: --testDetermine startup sequence, dump it and exit.
This is an option useful for debugging only.
--dump-configuration-items
Dump understood unit configuration items. This
outputs a terse but complete list of configuration items understood in unit
definition files.
--unit=
Set default unit to activate on startup. If
not specified, defaults to default.target.
--system, --user
For --system, tell systemd to run a
system instance, even if the process ID is not 1, i.e. systemd is not run as
init process. --user does the opposite, running a user instance even if
the process ID is 1. Normally, it should not be necessary to pass these
options, as systemd automatically detects the mode it is started in. These
options are hence of little use except for debugging. Note that it is not
supported booting and maintaining a full system with systemd running in
--system mode, but PID not 1. In practice, passing --system
explicitly is only useful in conjunction with --test.
--dump-core
Enable core dumping on crash. This switch has
no effect when running as user instance. This setting may also be enabled
during boot on the kernel command line via the systemd.dump_core=
option, see below.
--crash-vt=VT
Switch to a specific virtual console (VT) on
crash. Takes a positive integer in the range 1–63, or a boolean
argument. If an integer is passed, selects which VT to switch to. If
yes, the VT kernel messages are written to is selected. If no,
no VT switch is attempted. This switch has no effect when running as user
instance. This setting may also be enabled during boot, on the kernel command
line via the systemd.crash_vt= option, see below.
--crash-shell
Run a shell on crash. This switch has no
effect when running as user instance. This setting may also be enabled during
boot, on the kernel command line via the systemd.crash_shell= option,
see below.
--crash-reboot
Automatically reboot the system on crash. This
switch has no effect when running as user instance. This setting may also be
enabled during boot, on the kernel command line via the
systemd.crash_reboot= option, see below.
--confirm-spawn
Ask for confirmation when spawning processes.
This switch has no effect when run as user instance.
--show-status=
Takes a boolean argument or the special value
auto. If on, terse unit status information is shown on the console
during boot-up and shutdown. If off, no such status information is shown. If
set to auto behavior is similar to off, except that it is automatically
switched to on, as soon as the first unit failure or significant boot delay is
encountered. This switch has no effect when invoked as user instance. If
specified, overrides both the kernel command line setting
systemd.show_status= (see below) and the configuration file option
ShowStatus=, see systemd-system.conf(5).
--log-target=
Set log target. Argument must be one of
console, journal, kmsg, journal-or-kmsg,
null.
--log-level=
Set log level. As argument this accepts a
numerical log level or the well-known syslog(3) symbolic names
(lowercase): emerg, alert, crit, err,
warning, notice, info, debug.
--log-color=
Highlight important log messages. Argument is
a boolean value. If the argument is omitted, it defaults to true.
--log-location=
Include code location in log messages. This is
mostly relevant for debugging purposes. Argument is a boolean value. If the
argument is omitted it defaults to true.
--default-standard-output=, --default-standard-error=
Sets the default output or error output for
all services and sockets, respectively. That is, controls the default for
StandardOutput= and StandardError= (see systemd.exec(5)
for details). Takes one of inherit, null, tty,
journal, journal+console, syslog, syslog+console,
kmsg, kmsg+console. If the argument is omitted
--default-standard-output= defaults to journal and
--default-standard-error= to inherit.
--machine-id=
Override the machine-id set on the hard drive,
useful for network booting or for containers. May not be set to all
zeros.
--service-watchdogs=
Globally enable/disable all service watchdog
timeouts and emergency actions. This setting may also be specified during
boot, on the kernel command line via the systemd.service_watchdogs=
option, see below. Defaults to enabled.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
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, 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.
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.
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 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).
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 directoriesThe systemd system manager reads unit
configuration from various directories. Packages that want to install unit
files shall place them in the directory returned by pkg-config systemd
--variable=systemdsystemunitdir. Other directories checked are
/usr/local/lib/systemd/system and /usr/lib/systemd/system. User configuration
always takes precedence. pkg-config systemd
--variable=systemdsystemconfdir returns the path of the system
configuration directory. Packages should alter the content of these
directories only with the enable and disable commands of the
systemctl(1) tool. Full list of directories is provided in
systemd.unit(5).
User unit directories
Similar rules apply for the user unit
directories. However, here the XDG Base Directory specification[6] is
followed to find units. Applications should place their unit files in the
directory returned by pkg-config systemd --variable=systemduserunitdir.
Global configuration is done in the directory reported by pkg-config
systemd --variable=systemduserconfdir. The enable and
disable commands of the systemctl(1) tool can handle both global
(i.e. for all users) and private (for one user) enabling/disabling of units.
Full list of directories is provided in systemd.unit(5).
SysV init scripts directory
The location of the SysV init script directory
varies between distributions. If systemd cannot find a native unit file for a
requested service, it will look for a SysV init script of the same name (with
the .service suffix removed).
SysV runlevel link farm directory
The location of the SysV runlevel link farm
directory varies between distributions. systemd will take the link farm into
account when figuring out whether a service shall be enabled. Note that a
service unit with a native unit configuration file cannot be started by
activating it in the SysV runlevel link farm.
SIGNALS
SIGTERMUpon 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-irreversible.
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-irreversible. 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 2s 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-irreversible.
SIGRTMIN+4
Powers off the machine, starts the
poweroff.target unit. This is mostly equivalent to systemctl start
poweroff.target --job-mode=replace-irreversible.
SIGRTMIN+5
Reboots the machine, starts the reboot.target
unit. This is mostly equivalent to systemctl start reboot.target
--job-mode=replace-irreversible.
SIGRTMIN+6
Reboots the machine via kexec, starts the
kexec.target unit. This is mostly equivalent to systemctl start
kexec.target --job-mode=replace-irreversible.
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, SIGRTMIN+23
Sets the log level to "debug" (or
"info" on SIGRTMIN+23), as controlled via
systemd.log_level=debug (or systemd.log_level=info on
SIGRTMIN+23) on the kernel command line.
SIGRTMIN+24
Immediately exits the manager (only available
for --user instances).
SIGRTMIN+26, SIGRTMIN+27, SIGRTMIN+28
Sets the log target to
"journal-or-kmsg" (or "console" on SIGRTMIN+27,
"kmsg" on SIGRTMIN+28), as controlled via
systemd.log_target=journal-or-kmsg (or
systemd.log_target=console on SIGRTMIN+27 or
systemd.log_target=kmsg on SIGRTMIN+28) on the kernel command
line.
ENVIRONMENT
$SYSTEMD_LOG_LEVELsystemd reads the log level from this
environment variable. This can be overridden with --log-level=.
$SYSTEMD_LOG_TARGET
systemd reads the log target from this
environment variable. This can be overridden with --log-target=.
$SYSTEMD_LOG_COLOR
Controls whether systemd highlights important
log messages. This can be overridden with --log-color=.
$SYSTEMD_LOG_LOCATION
Controls whether systemd prints the code
location along with log messages. This can be overridden with
--log-location=.
$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
Controls where systemd looks for unit
files.
$SYSTEMD_SYSVINIT_PATH
Controls where systemd looks for SysV init
scripts.
$SYSTEMD_SYSVRCND_PATH
Controls where systemd looks for SysV init
script runlevel link farms.
$SYSTEMD_COLORS
The value must be a boolean. Controls whether
colorized output should be generated. This can be specified to override the
decision that systemd makes based on $TERM and what the console
is connected to.
$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.
KERNEL COMMAND LINE
When run as system instance systemd parses a number of kernel command line arguments[7]: 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 (VT) when it crashes. Defaults to disabled, meaning that no such
switch is attempted. If set to enabled, the VT the kernel messages are written
to is selected.
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 constant
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. auto behaves like
false until a unit fails or 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 auto. If specified overrides the
system manager configuration file option ShowStatus=, see
systemd-system.conf(5). However, the process command line option
--show-status= takes precedence over both this kernel command line
option and the configuration file option.
systemd.log_target=, systemd.log_level=,
systemd.log_location=, systemd.log_color
Controls log output, with the same effect as
the $SYSTEMD_LOG_TARGET, $SYSTEMD_LOG_LEVEL,
$SYSTEMD_LOG_LOCATION, $SYSTEMD_LOG_COLOR environment variables
described above. systemd.log_color 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, with the same effect as the
--default-standard-output= and --default-standard-error= command
line arguments described above, respectively.
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 --with-default-hierarchy= 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 --with-default-hierarchy= option). If the kernel does
not support unified cgroup hierarchy, the legacy hierarchy will be used even
if this option is specified.
quiet
Turn off status output at boot, much like
systemd.show_status=false 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).
SOCKETS AND FIFOS
/run/systemd/notifyDaemon 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[10], systemd-system.conf(5), locale.conf(5), systemctl(1), journalctl(1), systemd-notify(1), daemon(7), sd-daemon(3), systemd.unit(5), systemd.special(5), pkg-config(1), kernel-command-line(7), bootup(7), systemd.directives(7)NOTES
- 1.
- cgroups.txt
https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
- 2.
- Original Design Document
http://0pointer.de/blog/projects/systemd.html
- 3.
- Interface Stability Promise
https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise
- 4.
- Container Interface
https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
- 5.
- initrd Interface
https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface
- 6.
- XDG Base Directory specification
http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
- 7.
- If run inside a Linux container these arguments may be passed as command line arguments 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.
- 8.
- unified cgroup hierarchy
https://www.kernel.org/doc/Documentation/cgroup-v2.txt
- 9.
- legacy cgroup hierarchy
https://www.kernel.org/doc/Documentation/cgroup-v1/
- 10.
- systemd Homepage
https://www.freedesktop.org/wiki/Software/systemd/
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