system-control, systemctl, initctl, svcadm — process system control jobs, sending commands to the system manager and service manager
system-control {command} [arguments or options]
systemctl {command} [arguments or options]
initctl {command} [arguments or options]
svcadm {command} [arguments or options]
system-control takes a subcommand as
command that instructs it on what to do.
For limited systemd compatibility, it is also available as systemctl.
Not all subcommands are supported, nor is placing subcommand options before the command.
For similarly limited upstart compatibility, it is also available as initctl.
For similarly limited SunOS compatibility, it is also available as svcadm.
It operates in one of two modes, controlled by the {--user} command line option:
In "system" mode it operates on system-level state and services.
It potentially communicates with a System Manager process, which must be
process #1 and which it expects to recognize the same signals as
system-manager(1)
does.
It potentially communicates with a Service Manager process, such as
service-manager(1)
via a local domain socket at /run/service-manager/control
and via the control/status API of the individual services.
In "session" mode it operates on session-level state and services.
It potentially communicates with a Session Manager process, which again it expects to recognize the same signals as session-manager(1) does, and which is found either through the value of the $MANAGER_PID environment variable or through the getsid(2) library function.
(The latter will generally not find the right process, and it is recommended that you ensure that the $MANAGER_PID environment variable is correctly set.)
It potentially communicates with a Service Manager process, such as service-manager(1) via a local domain socket at /run/user/ and via the control/status API of the individual services.
$USER/service-manager/control.$SID
Services and targets are defined by bundle directories.
Although there is no constraint enforced, and system-control simply follows symbolic links, by convention service bundle directories generally live under /etc/service-bundles/services, /run/service-bundles/services, or /var/sv; and target bundle directories generally live under /etc/service-bundles/targets.
A service is generally a daemon process that runs. A target is generally a collection of services that are started/stopped together.
The start and stop subcommands construct jobs, which comprise a set of actions. Each action is a start or a stop command to the control API of a service/target. Jobs are composed by starting with an action on a named service, and then following information in the service bundles to related services and targets. The service bundles also determine the order in which the actions are taken.
A start action simply requests that the service manager bring the
service/target to the "running" state, if it isn't already there.
A stop action, however, is more complex.
Initially it requests that the service manager bring the service/target to the
"stopped" state (if it isn't already there).
However, if that does not happen within 60 seconds, it requests that the
service manager send the SIGKILL signal to the service/target.
A bundle directory contains the command information, dependency information, relationship information, and control/status API for a service. It contains various subdirectories (which can be symbolic links to directories elsewhere):
The service/ and supervise/
subdirectories are (respectively) the service and supervise directories for the
service, comprising the command information and the control/status API.
See
service-manager(1)
for what service and supervise directories contain.
(service-dt-scanner(1)
implements a slight extension here, for compatibility.)
When bundles are on a read-only filesystem, such as a CD-ROM,
supervise must be a symbolic link pointing to a directory
on a read-write filesystem, since supervise directories must be writable.
One might choose a subdirectory of
/run/service-bundles/early-supervise/ for example.
system-control attempts to create the target of such a
symbolic link before attempting to load the service, to avoid a chicken-and-egg
situation with "sysinit" services that are set up this way.
The wants/, conflicts/,
wanted-by/, stopped-by/, and
required-by/
subdirectories comprise dependency or dependency installation information.
Each contains a set of symbolic links to other bundle directories for other services.
wants/ contains links to services that the current service
"wants".
Starting the current service implies starting the linked-to service as well.
conflicts/ contains links to services that "conflict" with the current service.
Starting the current service implies stopping the linked-to services.
required-by/ contains links to services that "require" the current service.
Stopping the current service implies stopping the linked-to services as well.
wanted-by/ contains links to (standard) targets that should "want"
the current service when it is enabled.
Enabling the service places it in the targets' "wants" lists, and disabling the service removes it.
stopped-by/ contains links to (standard) targets that
should "conflict" with the current service when it is enabled.
Enabling the service places it in the targets' "conflicts" lists, and disabling the service removes it.
The after/ and before/ subdirectories comprise
relationship information.
Relationships govern the ordering between the individual actions in a start/stop job.
after/ contains links to services that should be started
after/stopped before the current service when executing a start/stop job.
before/ contains links to services that should be started
before/stopped after the current service when executing a start/stop job.
Relationships are not the same as dependencies.
A service can "want" another service without having any ordering against it with respect
to start/stop actions.
Indeed, this is a common case for system targets.
The normal target, for example, "wants" the
server, workstation, and
multi-user targets (and by extension everything that they
in their turn "want"), but all of the wanted services are started in parallel
with the normal target itself.
Similarly, a service can be ordered with respect to another service without having a dependency from it.
For example, both "log" and "main" services are "wanted" by the server and workstation targets, explicitly.
The individual "main" services, therefore, only need to be ordered after their corresponding "log" services, and do not "want" them.
("log" services are first-class citizens in this respect.)
There are no implicit relationships or dependencies in a bundle. The relationships and dependencies are exactly what is explicitly in the filesystem. system-control will fail if the recorded relationships and dependencies are self-contradictory or impossible (such as a service that conflicts with itself, for example).
Several subcommands take a list of bundle names... .
Each name can be the full absolute pathname of a bundle directory or a relative pathname with a directory prefix, in which case it is used as-is, or a bundle directory name without any directory prefix, in which case a set of standard locations is searched for a bundle directory by that name.
The search algorithm is as follows:
A name that ends in
.target is searched for (sans the .target suffix)
in the standard locations for target bundles:
/run/service-bundles/targets/
/etc/service-bundles/targets/
/var/service-bundles/targets/
A name that ends in
.service or .socket is searched for (sans those
suffixes) in the standard locations for service bundles:
/run/service-bundles/services/
/etc/service-bundles/services/
/var/local/sv/
/var/sv/
/var/svc.d/
/service/
Any other name is searched
for (as-is) in the standard locations for service and for target bundles.
If the path search fails, the name is simply assumed to name a bundle directory in the current directory.
system-control {reboot} [ -f | --force ]
system-control {halt} [ -f | --force ]
system-control {poweroff} [ -f | --force ]
system-control {emergency}
system-control {rescue}
system-control {normal}
system-control {init} [--user] [ -o | --update ] [ -s | --single ] [ -b | --emergency ] [-a] [-f] [-z string] [runlevel(s)...]
Those subcommands communicate with the system manager to change system state. system-control sends a signal to process #1 using the kill(2) system call. It will fail if it does not have the necessary privileges for sending a signal to that process.
| command | signal | |
| on BSD | on Linux | |
| reboot | SIGINT | SIGRTMIN + 5 |
| reboot -f | SIGRTMIN + 15 | |
| poweroff | SIGUSR2 | SIGRTMIN + 4 |
| poweroff -f | SIGRTMIN + 14 | |
| halt | SIGUSR1 | SIGRTMIN + 3 |
| halt -f | SIGRTMIN + 13 | |
| emergency | SIGRTMIN + 2 | |
| rescue | SIGTERM | SIGRTMIN + 1 |
| normal | SIGRTMIN + 0 | |
| init -b | emergency | SIGRTMIN + 2 | |
| init -s | 1 | S | s | single | SIGRTMIN + 10 | |
SIGTERM | SIGRTMIN + 1 | |
| init H | h | SIGUSR1 | SIGRTMIN + 3 |
| init 0 | SIGUSR2 | SIGRTMIN + 4 |
| init 6 | SIGINT | SIGRTMIN + 5 |
| init [ 2 | 3 | 4 | 5 | m | auto ] | SIGRTMIN + 10 | |
SIGRTMIN + 0 | ||
Exactly how the system powers off, halts, reboots, switches to normal, emergency, or rescue modes, and so forth is entirely up to whatever is running as process #1, which is expected to be in charge of system state. These subcommands do nothing except send the signals to command the system manager. They do not directly enact any system state change themselves. In part this is because that would open up the possibility of the service manager killing the process that was (partway through) enacting the state changes, if a state change happened to affect the service running the system-control command.
The [--force] command line argument is used within the various targets and is intended to cause the system manager to proceed directly to the finalization action.
The init subcommand is spawned by system-manager(8) and session-manager(8) as their initial action. They pass it the command line arguments that they themselves were invoked with. As such, its command line syntax is modelled on what boot loaders and kernels tend to supply to process #1, which is a largely undocumented and non-standardized mixture of old-style runlevels and options.
In normal and rescue modes it sends two signals to process #1, instituting a two-phase initialization sequence similar to the FILESYSTEMS milestone mechanism in BSD operating systems.
The first phase, the sysinit target, is expected to initialize as much of the system as necessary so that the second phase, the normal or rescue target, can find all service and target bundles, including those that are not on the root filesystem.
There is no q runlevel.
This is deliberate.
Its use case is running telinit q after updating /etc/ttys or /etc/inittab.
Any script that is updating those files and then expecting the system manager to re-read them is not targetting the correct configuration mechanisms, and is in error.
LILO, the FreeBSD loader(8), GRUB, and others may cause -a or -f options to be passed. Their meanings are non-standard, largely or even wholly undocumented, inconsistent across platforms and toolsets, considered obsolete in their original forms, and without application here. The -z option is a dummy space-taker that is also used by such systems. All three options are ignored. The --update command line option is reserved for future use.
system-control { start | activate } [names...]
system-control { stop | deactivate } [names...]
system-control {isolate} [names...]
system-control {reset} [names...]
These subcommands process one or more jobs, sending messages to the service manager to start or to stop one or more services. Jobs may also involve invoking any number of configurable actions. Jobs processing tries to ensure that service dependencies are correctly maintained and processed. To control services directly and individually without regard for dependencies, use service-control(8).
The reset command is intended to be used by package installer programs. It is translated into either start or stop according to whether the service is enabled or disabled. This allows package installers to remain in blissful ignorance of whether a service should be started or stopped after installing the package for it. Instead, the package installer simply executes the preset command and then the reset command and the service is started or stopped according to whatever the administrator has chosen.
The isolate subcommand exists for compatibility, and is equivalent to start.
system-control {enable} [names...]
system-control {disable} [names...]
system-control {preset} [--prefix prefix] [--no-system] [--no-rcconf] [--ttys] [--dry-run] [names...]
These subcommands enable or disable one or more services or targets, so that they do or do not automatically start when one of the standard targets is started and automatically stop when the shutdown standard target is started.
Each service bundle specifies a (symbolically linked) list of target bundles in its wanted-by/ directory.
Usually these will be the workstation, server, or multi-user standard targets.
For each bundle, enabling the service involves symbolically linking its bundle directory into the target bundle's wants/ list, and disabling the service involves removing that link.
Each service bundle also specifies a (symbolically linked) list of target bundles in its stopped-by/ directory.
Usually these will be the shutdown standard target.
For each bundle, enabling the service involves symbolically linking its bundle directory into the target bundle's conflicts/ and after/ lists, and disabling the service involves removing those links.
The preset command is intended to be used by package installer programs. It is translated into either enable or disable according to a system/administrator-supplied preset flag (unless the --dry-run command line argument is used, causing it to take no actual action). This allows package installers to remain in blissful ignorance of whether a service should be enabled or disabled after installing the package for it. Instead, the package installer simply executes the preset command and the service is set to whatever enabled or disabled status the administrator has chosen.
The service/socket/target that is preset is prefixname, with prefix specifiable via the --prefix command line argument.
Preset information can be taken from one of several sources:
(unless the --no-system command line option is set)
systemd and system-manager preset information given in *.preset files in the following directories:
/etc/system-control/presets/
/etc/systemd/system-preset/
/usr/share/system-control/presets/
/lib/systemd/system-preset/
/usr/lib/systemd/system-preset/
/usr/local/etc/system-control/presets/
/usr/local/lib/systemd/system-preset/
systemd has four places for preset files.
Although its doco lists one more (/run/systemd/system-preset) this is not actually the case and it would be ephemeral anyway; so preset does not look at it either.
In addition to those preset looks in extra directories where systemd presets can be overridden by system-manager-specific information; allowing a system administrator or package writer to preset things one way for systemd and another way for the preset command.
As with systemd earlier preset directories override later ones;
the contents of files with lexically earlier names override the contents of files with lexically later names;
and
the default state, in the absence of an explicit preset, is "enabled".
Directives are matched against
prefixname.
(unless the --no-rcconf command line option is set)
/etc/rc.conf and /etc/rc.conf.local
preset information, specifically the
name_enabletrue, 1, yes,
and on as enable, and any other values (including specifically
false, 0, no, and off) as
disable.
The variable names are matched against just name to allow one to use a main service name as name and combine it with a log service template prefix such as cyclog@ or s6-multilog@, on the grounds that traditional /etc/rc.conf and /etc/rc.conf.local contents do not make explicit provision for separate logging services.
(if the --ttys command line option is set)
/etc/ttys
preset information, specifically the on and off flags
as enable and disable, respectively.
The onifconsole flag is also recognized and processed with reference to the currently active console device (on BSD systems only).
If /etc/ttys does not exist, as is usually the case on Linux operating systems, all TTYs default to preset enabled.
The terminal names are matched against just name.
This allows one to use an ordinary TTY device name as name and combine it with a "templatized" bundle name prefix such as
ttylogin@,
getty@,
or
autovt@.
(if the --fstab command line option is set)
/etc/fstab preset information, specifically the noauto flag as disable.
The device and directory names are matched against just name, after unescaping it.
This allows one to use an ordinary device or directory name as name and combine it with a "templatized" bundle name prefix such as
mount@,
fsck@,
swap@,
or
dump@.
This is designed in particular for use with service bundles generated by the convert-fstab-services subcommand.
system-control {status} [names...]
system-control {show} [names...]
system-control {find} [names...]
system-control { try-restart | condrestart | force-reload } [names...]
system-control {is-active} [names...]
system-control {is-loaded} [names...]
system-control {is-enabled} [names...]
system-control takes each of the [names...], searches for the corresponding service bundle directory, constructs a list of directory names, and chains to other commands with those directory names as arguments:
| subcommand | chains to |
| status | service-status(1) |
| show | service-show(1) |
| show-json | service-show(1) --json |
| find | ls(1) -1d |
| try-restart | service-control(1) --terminate |
| is-active | service-is-up(1) |
| is-loaded | service-is-ok(1) |
| is-enabled | service-is-enabled(1) |
system-control {convert-systemd-units} [--bundle-root root] [--alt-escape] [--etc-bundle] [--escape-instance] [--no-sytemd-quirks] { name.target | name.socket | name.service | name@parameter.service }
This subcommand takes some systemd unit files and generates from them a service bundle in the current directory (or in the root directory) that contains scripts, dependencies, and autoboot dependency configuration information.
The bundle is not enabled by the conversion process, but can be started and enabled as it stands, with the start and preset subcommands, just like any other service bundle.
The systemd unit files are determined from the argument.
If name.targetname/
If name.socketAccept=true, then it is combined with a name@.servicename/
If name.socketAccept=false, then it is combined with a name.servicename/
If name.servicename/
If name@parameter.serviceparameter for parameter substitution into a service bundle directory named name@parameter/
Normally parameter is taken to be the escaped form and is unescaped during parameter substitution.
This is generally used where parameter represents something in the filesystem, but has had to be pre-escaped in order to result in a service name without pathname components.
If the --escape-instance option is used, then parameter is instead taken to be the original, unescaped, pathname form and will be escaped into its service name form.
The normal escaping algorithm is the conventional systemd one that escapes / and -.
If the --alt-escape option is used, then an alternative escaping algorithm that escapes
/,
\,
,,
:, and
@
is used instead.
The --alt-escape and --escape-instance options are generally used together, such that the parameter is the unescaped service bundle directory name and the escaped form is (for example) an account name in an account database.
Unit files can reference other services.
The assumption is that all service bundles are under one common root and all target bundles under another; so service-to-service dependencies and orderings can be relative pathnames whilst service-to-target and target-to-service dependencies and orderings have to be absolute pathnames.
The --etc-bundle option changes this assumption, such that target bundles are now assumed to be reachable with relative pathnames from the converted service bundle; as is the case for special early bootstrap service bundles that live in /etc/service-bundles/services/.
It also forces the bundle to be marked as an EarlySupervise bundle whose supervise/ directory lives in a tmpfs.
Conversion of every possible systemd unit file to a service bundle requires a human being. This subcommand converts systemd units that fall within certain bounds, which (given that most services are fairly simple) should be the majority of systemd units in existence. These bounds are:
The service must be a simple, forking, or oneshot service. DBus and notify services are not converted. For best results, avoid having forking services in the first place, and change them into simple services wherever possible.
Only TCP, UDP, local domain datagram, local domain stream, and netlink datagram sockets are converted.
The run/service script makes use of
udp-socket-listen(1),
tcp-socket-listen(1),
local-datagram-socket-listen(1),
local-stream-socket-listen(1),
netlink-datagram-socket-listen(1),
tcp-socket-accept(1), and
local-stream-socket-accept(1)
to spawn services, either to listen to the accepting socket or to respond on connecting sockets.
FIFOs and sequential packet sockets are not supported, in the absence of similar tools.
Some of the more esoteric mechanisms, and any undocumented settings, in systemd are not converted. The converter will print a warning for any setting in the unit files that it does not use for conversion. These will include:
Specialized options for conditionally enabling the service, such as conditionpathexists and conditiondirectorynotempty, are not converted.
These are almost always in practice used to make services run on specific platforms and not on others, or dependent from the presence of installed packages, and should be replaced with hooks into the preset mechanism.
Other highly specialized options that even systemd recommends against, such as fsckpassno, are not converted.
Specialized options for TTY management, such as standardinput=tty-force, are not converted.
Instead of these, employ the
vc-get-tty(1),
open-controlling-tty(1),
and related utilities in the run script.
Non-standard substitutes for SIGTERM via killsignal are not converted.
In practice, this is primarily used to substitute SIGHUP for use with "services" that are actually interactive login shells.
Linux-only mechanisms such as capabilityboundingset, I/O scheduling, and control groups are not converted.
This is merely down to a lack of known chaining commands for manipulating those mechanisms.
The --no-systemd-quirks turns off the handling of the systemd quirks that are discussed in detail in the Nosh Guide. It is an alternative to turning off the quirks with the various (extra to systemd) unit file directives.
system-control {convert-fstab-services} [--etc-bundle] [--bundle-root root]
This subcommand takes the entries in /etc/fstab and generates from them a set of service bundles in the current directory (or in the root directory) that contains scripts, dependencies, and autoboot dependency configuration information.
For each swap entry:
It always creates a swap@ bundle.
The bundle is created as devicewanted-by/ either the system swapauto.target or the system swaplate.target, so that it is started during autoboot when it is enabled.
The choice depends from whether the entry is marked late.
If the entry is marked discard then it creates a bundle that passes the --discard flag to swapon(8).
If the entry is marked pri= then it creates a bundle that passes the --priority NN flag.
It always creates a dump@ bundle.
The bundle is created as devicewanted-by/ the system dumpauto.target, so that it is started during autoboot when it is enabled.
For each non-swap entry:
It always creates a mount@ bundle.
The bundle is created as directorywanted-by/ the system local-fs.target or the system remote-fs.target, depending from the filesystem type listed.
This so that it is started during autoboot when it is enabled.
The list of types that are considered to be "remote" is a superset of the old Debian list from mountall.sh, with a few additions from the BSDs.
"API" filesystems (see system-control(1)) and the root filesystem are specially handled:
They are assumed already mounted by the time that service management starts, and are thus mounted with the "remount"/"update" flag.
The root is required to remain mounted beyond service management termination, and thus it is merely remounted/updated to read-write at start and to read-only at stop.
If the entry specifies a "pass" number that is greater than zero, it also creates fsck@ bundle.
It is ordered directorybefore/ the respective mount@ bundle, and is directorywanted-by/ it.
So when the bundle is enabled fsck is run before the volume is actually mounted.
The bundles are not enabled by the conversion process, but can be started and enabled as they stand, with the start and preset subcommands, just like any other service bundle. With preset the --fstab option is appropriate of course.
The assumption is that all service bundles are under one common root and all target bundles under another; so service-to-service dependencies and orderings can be relative pathnames whilst service-to-target and target-to-service dependencies and orderings have to be absolute pathnames.
The --etc-bundle option changes this assumption, such that target bundles are now assumed to be reachable with relative pathnames from the converted service bundle; as is the case for special early bootstrap service bundles that live in /etc/service-bundles/services/.
It also forces the bundle to be marked as an EarlySupervise bundle whose supervise/ directory lives in a tmpfs.
system-control {nagios-check-service} [--min-seconds seconds] [--critical-if-below-min] {name...}
This subcommand is intended for use as a Nagios plug-in.
It queries the status API in the bundle directory for service/target name .
If the service is up for longer than seconds seconds it returns a Nagios "OK" status.
If the service is up, but for less than seconds seconds it returns a Nagios "WARNING" status and prints a line containing the service bundle directory name.
It does the same if the service is still in the process of being loaded by the service manager, or in the starting or stopping states.
The --critical-if-below-min command line option changes the status returned for such up services to "CRITICAL", but does not alter the treatment of starting or stopping services.
If the service is unexpectedly down or unloaded, if the status API reports the service running in the future (because of clock skew somewhere), or if the service is in the failing state, it returns a Nagios "CRITICAL" status and prints a line containing the service bundle directory name.
system-control {load-kernel-module} {module...}
system-control {unload-kernel-module} {module...}
These subcommands provide a minimal operating-system-neutral kernel module loading and unloading mechanism, for use in cross-platform service bundles. They devolve to the appropriate operating system commands, which are kldload(8) and kldunload(8) on BSD and modprobe(8) (without or with the --remove option) on Linux.
system-control {cat} [names...]
system-control takes each of the [names...], searches for the corresponding service bundle directory, changes to the corresponding service directory, and runs grep(1) to dump the contents of the start, stop, run, and restart files.
system-control {set-service-env} {var} [value]
system-control {print-service-env} [var]
If the service has an environment template subdirectory named env/ (in the format understood by envdir(1)), these subcommands can be used to manipulate that template.
set-service-env var value sets var to value in the template, the change not (of course) affecting any currently running service.
set-service-env var specifies that the template unset var, the change not (of course) affecting any currently running service.
print-service-env var prints (only) the value of var from the template.
print-service-env prints the whole template as list of var=value entries.
Several standard targets are defined.
They conventionally live in the /etc/service-bundles/targets/ directory.
These standard targets are (indirectly) started by the init subcommand.
normal
This target is the normal target started by the init subcommand. This should bring up with it all of the services involved in the normal operation of the system, and an administrator-defined set of multiple login user interfaces that may include both TUI and GUI login prompts.
It "wants" the workstation, server, and multi-user targets.
Thus starting it starts the union of all services wanted by those targets.
It is not ordered with respect to those targets.
So in the absence of orderings in between the individual services wanted by those targets, defined in their bundles, all wanted workstation, server, and multi-user services are brought up in parallel.
emergencyThis target is the target started by the init subcommand with the [-b] option. Starting it is intended to bring up the system in "emergency mode", bringing up no services, mounting no (non-system) volumes, and bringing up just "emergency mode" services, such as a secure login on the default terminal.
It "wants" no other targets or services. So in "emergency mode" (if nothing else has been started) only the system filesystems are available, and not necessarily even read-write.
rescueThis target is the target started by the init subcommand with the [-s] option. Starting it is intended to bring up the system in "rescue mode", bringing up with it the fundamental system initialization services and a secure login user interface.
It "wants" the sysinit target, but not the basic target.
updateThis target is the target started by the init subcommand with the [--update] option. Starting it is intended to bring up the system in "update mode", bringing up with it the fundamental system initialization services and the system update utility.
It "wants" the sysinit target, but not the basic target.
The poweroff, halt, and reboot subcommands invoke several standard targets indirectly.
poweroff, halt, reboot
These three targets both "want" the shutdown target and order themselves to start after it.
Thus starting them shuts down all services and then, once this has been done, starts these targets.
They are usually started by the System Manager, in response to system control commands requesting system reboot, halt, or power off.
When they (finally) start, they invoke the reboot, halt, and poweroff subcommands of system-control with the {-f} command-line option.
This signals the System Manager to enact the actual reboot, halt, or power-off action.
For example: When system-manager(8) is process #1, system halt operates as follows:
The superuser runs system-control {halt}.
This sends SIGUSR1 (on BSD) or SIGRTMIN + 3 (on Linux) to the system manager process.
In response to that signal, the system manager runs system-control {activate} halt .
system-control does everything necessary for activating the halt target, including stopping all other (conflicting) services and targets.
In the service control ordering starting the halt target comes after processing every other service, because of the ordering between halt and shutdown and between shutdown and everything else.
When the halt target is finally started it runs system-control {halt} {-f}.
This sends SIGRTMIN + 13 to the system manager process.
In response to that signal, the system manager performs the finalization action of actually telling the operating system kernel to halt the system, after various standard system shutdown actions such as flushing the filesystem cache.
Other standard targets are started by telinit(1).
User-supplied services and targets that are auto-started at system bootstrap should list themselves in the wants/ and conflicts/ lists of subordinate targets (via the enable and disable subcommands).
These targets are usually not started explicitly.
workstation
All services that normally form part of bringing the system up as a "workstation" should be listed in this target's wants/ list.
Such services will include things such as the cron(1) daemon.
This target "wants" the basic target, so starting it (directly or indirectly) will bring the basic system up.
It is a collection that is used to group services, but is not an ordering milestone and has no before/ or after/ relationships.
server
All services that normally form part of bringing the system up as a "server" should be listed in this target's wants/ list.
Such services will include things such as HTTP/FTP/SMTP daemons, and daemons that provide services over the network.
This target "wants" the basic target, so starting it (directly or indirectly) will bring the basic system up.
It is a collection that is used to group services, but is not an ordering milestone and has no before/ or after/ relationships.
multi-user
All services that normally form part of bringing up multi-user logins should be listed in this target's wants/ list.
Such services will include things such as the login services for terminals (real and virtual) and X.
This target "wants" the basic target, so starting it (directly or indirectly) will bring the basic system up.
It is a collection that is used to group services, but is not an ordering milestone and has no before/ or after/ relationships.
shutdown
Starting this target is intended to shut down all running normal services.
All normal services should be in this target's conflicts/ list.
It is also an ordering milestone, in that all services listed in its conflicts/ list should also be listed in its after/ list.
shutdown is then listed in the after/ list of the poweroff, halt, and reboot target to ensure that they are only started after the system has entered "shutdown mode".
unmount
Starting this target is intended to unmount all filesystems, both local and remote.
All mount@* services should be in this target's conflicts/ list.
unmount is then listed in the after/ list of the poweroff, halt, and reboot target to ensure that they are only started after the system has unmounted all filesystems.
Core services and targets are incorporated into a set of further subordinate targets.
basic
This target implies the "basic" system, excluding all workstation, server, and multi-user services.
It "wants" the sysinit target.
It is a collection that is used to group services, but is not an ordering milestone and has no before/ or after/ relationships.
sysinit
All fundamental system initialization services and steps should be listed in this target's wants/ list.
Such services will include things such as the hostname service that runs set-dynamic-hostname(1), the machine-id service that runs setup-machine-id(1), the local-fs target, and the remote-fs target.
It is a collection that is used to group all such services, but is not an ordering milestone and has no before/ or after/ relationships.
local-fs
This "local filesystems" target is an ordering milestone and a collection, in that all services listed in its wants/ list should also be listed in its after/ list.
All system initialization services and steps for checking and mounting local filesystems, including remounting the root filesystem in read-write mode, should be in those lists.
One can thus list local-fs in the after/ list of a service or target to ensure that it is only brought up after local filesystems have been mounted and checked.
Note that services encompassed by this target may not rely upon filesystems being checked and mounted, nor upon the root filesystem being mounted read-write.
To handle the latter, in particular, their supervise/ subdirectories should be symbolic links to a suitable subdirectory of /run/service-bundles/early-supervise.
remote-fs
This "remote filesystems" target is an ordering milestone and a collection, in that all services listed in its wants/ list should also be listed in its after/ list.
All system initialization services and steps for checking and mounting remote filesystems should be in those lists.
One can thus list remote-fs in the after/ list of a service or target to ensure that it is only brought up after remote filesystems have been mounted and checked.
local-fs-pre
This "local filesystems precursor" target is not a collection; its wants/ list should be empty.
It is solely an ordering milestone, that is brought in only if the services that want to order before it are themselves brought in.
It exists because system initialization services that need to occur before any filesystem checks or mounts, usually special services that initialize an interactive UI for fsck(1), do not have another way to hold the checks/mounts from commencing until they are done.
Such services should list this target in their before/ lists and wants/ lists.
Filesystem checks and mounts should list this target (only) in their after/ lists, so that they order relative to it if the target is brought in but do not themselves bring it in.
name-services
This target is not a collection.
It is solely an ordering milestone, that is brought in only when the services that want to order before it are themselves brought in.
It exists because some name/address services lookup clients cannot be caused via the client-server communications mechanism itself to block indefinitely until the server is ready; and so have to have an explicit ordering to order them before any respective servers.
One lists name-services in the after/ list of a service or target to ensure that it is only brought up after such name/address lookup services are available.
By not including it in their wants/ lists, however, they do not themselves being it in if there are no name/address lookup services that require hard ordering.
All services that are involved in providing local name/address lookup services should be listed in its after/ and its wants/ lists.
swapauto
This target is a collection that is wanted by "sysinit"; it is not an ordering milestone.
All "auto" "swap" services should be listed in its wants/ lists.
swaplate
This target is a collection that is wanted by "sysinit"; it is not an ordering milestone.
All "late" "swap" services should be listed in its wants/ lists.
dumpauto
This target is a collection that is wanted by "sysinit"; it is not an ordering milestone.
All "dump" services should be listed in its wants/ lists.