Systemd

Units

List units

As you can see, there are hardware and software related units.

# systemctl list-units
  UNIT                                                            LOAD   ACTIVE SUB       DESCRIPTION
  proc-sys-fs-binfmt_misc.automount                               loaded active running   Arbitrary Executable File Formats File System Automount Point
  sys-devices-pci0000:00-0000:00:02.0-backlight-acpi_video0.device loaded active plugged   /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
  sys-devices-pci0000:00-0000:00:02.0-drm-card0-card0\x2dLVDS\x2d1-intel_backlight.device loaded active plugged   /sys/devices/pci0000:00/0000:00:02.0/drm
  sys-devices-pci0000:00-0000:00:19.0-net-eth0.device             loaded active plugged   82579LM Gigabit Network Connection
  sys-devices-pci0000:00-0000:00:1a.0-usb1-1\x2d1-1\x2d1.4-1\x2d1.4:1.0-bluetooth-hci0-rfkill3.device loaded active plugged   /sys/devices/pci0000:00/0000
  sys-devices-pci0000:00-0000:00:1a.0-usb1-1\x2d1-1\x2d1.4-1\x2d1.4:1.0-bluetooth-hci0.device loaded active plugged   /sys/devices/pci0000:00/0000:00:1a.0
  sys-devices-pci0000:00-0000:00:1b.0-sound-card0.device          loaded active plugged   6 Series/C200 Series Chipset Family High Definition Audio Contro
  sys-devices-pci0000:00-0000:00:1c.1-0000:03:00.0-ieee80211-phy0-rfkill2.device loaded active plugged   /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0
  sys-devices-pci0000:00-0000:00:1c.1-0000:03:00.0-net-wlan0.device loaded active plugged   Centrino Advanced-N 6205 [Taylor Peak] (Centrino Advanced-N 62
  sys-devices-pci0000:00-0000:00:1d.0-usb2-2\x2d1-2\x2d1.4-2\x2d1.4:1.1-tty-ttyACM0.device loaded active plugged   F5521gw
  sys-devices-pci0000:00-0000:00:1d.0-usb2-2\x2d1-2\x2d1.4-2\x2d1.4:1.3-tty-ttyACM1.device loaded active plugged   F5521gw
...
  session-c2.scope                                                loaded active running   Session c2 of user lollypop
  accounts-daemon.service                                         loaded active running   Accounts Service
● anacron.service                                                 loaded failed failed    Run anacron jobs
  apparmor.service                                                loaded active exited    LSB: AppArmor initialization
  apport.service                                                  loaded active exited    LSB: automatic crash report generation
...

In this example you can see that the anacron.service failed to start.

Display unit status

# systemctl status anacron
● anacron.service - Run anacron jobs
   Loaded: loaded (/lib/systemd/system/anacron.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fr 2015-08-28 09:18:13 CEST; 31min ago
  Process: 1591 ExecStart=/usr/sbin/anacron -dsq (code=exited, status=1/FAILURE)
 Main PID: 1591 (code=exited, status=1/FAILURE)

Aug 28 09:18:13 lollybook systemd[1]: Started Run anacron jobs.
Aug 28 09:18:13 lollybook systemd[1]: Starting Run anacron jobs...
Aug 28 09:18:13 lollybook systemd[1]: anacron.service: main process exited, code=exited, status=1/FAILURE
Aug 28 09:18:13 lollybook anacron[1591]: anacron: Can't chdir to /var/spool/anacron: No such file or directory
Aug 28 09:18:13 lollybook systemd[1]: Unit anacron.service entered failed state.
Aug 28 09:18:13 lollybook systemd[1]: anacron.service failed.

Ah, deleted the anacron spool directory. ;-)

Restart units

Fix the problem and restart the service.

root@lollybook:~# mkdir /var/spool/anacron
root@lollybook:~# systemctl restart anacron.service
root@lollybook:~# systemctl status anacron
● anacron.service - Run anacron jobs
   Loaded: loaded (/lib/systemd/system/anacron.service; enabled; vendor preset: enabled)
   Active: active (running) since Fr 2015-08-28 09:53:49 CEST; 4s ago
 Main PID: 5179 (anacron)
   CGroup: /system.slice/anacron.service
           └─5179 /usr/sbin/anacron -dsq

Aug 28 09:53:49 lollybook systemd[1]: Started Run anacron jobs.
Aug 28 09:53:49 lollybook systemd[1]: Starting Run anacron jobs...
Aug 28 09:53:49 lollybook anacron[5179]: Anacron 2.3 started on 2015-08-28
Aug 28 09:53:49 lollybook anacron[5179]: Will run job `cron.daily' in 5 min.
Aug 28 09:53:49 lollybook anacron[5179]: Will run job `cron.weekly' in 10 min.
Aug 28 09:53:49 lollybook anacron[5179]: Will run job `cron.monthly' in 15 min.
Aug 28 09:53:49 lollybook anacron[5179]: Jobs will be executed sequentially

Display unit declaration

# systemctl cat zfs.target
# /lib/systemd/system/zfs.target
[Unit]
Description=ZFS startup target
Requires=zfs-mount.service
Requires=zfs-share.service
Wants=zed.service

[Install]
WantedBy=multi-user.target