systemd #1

# shows required and wanted units of the specified unit
# target units are recursively expanded
# do not use patterns here
systemctl list-dependencies cron
# all other units are recursively expanded as well
systemctl --all list-dependencies
# units with dependencies of type Wants= or Requires= on the given unit
systemctl --all --reverse list-dependencies cron.service

# list known units
systemctl --full list-units

# available unit types
systemctl --type=help

# show all loaded units, regardless of their state, including inactive units
systemctl --full --all list-units

# certain unit types
systemctl --full --all --type=device,mount list-units

systemctl --full --all --state=inactive list-units
systemctl --full --all --state=listening,running list-units

# units in failed state
systemctl --full --all --state=failed list-units

# list socket units
# show the type of the socket
systemctl --show-types list-sockets

# show backing files of one or more units
systemctl cat cron

# checks whether any of the specified unit files are enabled
# do not use patterns here
systemctl is-enabled cron.service

# enable one or more unit files or unit file instances
# [Install] section of a unit file is used exclusively by the enable and disable commands of the systemctl tool during installation of a unit
# creates only the suggested symlinks for the unit; the administrator is free to make additional changes manually by placing or removing symlinks in the directory (make sure to invoke daemon-reload manually); the disable command removes all symlinks to the unit files including manual additions, not just those actually created by enable
# will create a number of symlinks as encoded in the "[Install]" sections of the unit files
# the preferred way to create symlinks in the .wants/ directory of a unit file
# the systemd configuration is reloaded
# does not have the effect of also starting any of the units being enabled
# simply hooks the unit into various suggested places (for example, so that the unit is automatically started on boot or when a particular kind of hardware is plugged in)
# note that units may be started without being enabled
# in case of instance enablement, symlinks named the same as instances are created in the install location, however they all point to the same template unit file
systemctl enable cron.service

# changes are not made in subdirectories of /etc but in /run, with identical immediate effects, however, since the latter is lost on reboot, the changes are lost too
systemctl --runtime enable

# enables the unit for all future logins of all users
systemctl --global enable

# reenable one or more unit files
# a combination of disable and enable and is useful to reset the symlinks a unit is enabled with to the defaults configured in the "[Install]" section of the unit file
systemctl reenable cron.service

# resets all installed unit files to the defaults configured in the preset policy file
systemctl preset cron.service

# reload all unit files and recreate the entire dependency tree
systemctl daemon-reload

# link units to /dev/null
# it prohibits all kinds of activation of the unit, including manual activation
# if a unit file is empty (i.e. has the file size 0) or is symlinked to /dev/null, its configuration will not be loaded and it appears with a load state of "masked"
# also honors --runtime
systemctl mask cron.service

# check whether any of the specified units are active (i.e. running)
systemctl is-active cron

# show the status of all units
systemctl --full --all status

systemctl --full status cron

# show information about the unit the process belongs to
systemctl --full status 871

# show system status
systemctl status

# properties of the manager
systemctl show

systemctl --no-pager show --property=MainPID,ExecStart cron

# shutdown of all running services is skipped, however all processes are killed and all file systems are unmounted or mounted read-only, immediately followed by the system halt
systemctl --force halt

# trigger system recovery
systemctl reboot recovery

systemctl suspend
systemctl hibernate
systemctl hybrid-sleep

# intended for usage in initial RAM disks ("initrd"), and will transition from the initrd's system manager process (a.k.a "init" process) to the main system manager process
# if the system manager path is omitted or equal to the empty string, the state of the initrd's system manager process is passed to the main system manager, which allows later introspection of the state of the services involved in the initrd boot
systemctl switch-root ...

# a short help text
systemctl --help