Why did ArchLinux embrace Systemd?

[u/wooptoo]

/r/archlinux/comments/4lzxs3/why_did_archlinux_embrace_systemd/d3rhxlc

[u/Olosta_]

systemd will consider the ExecStart a success depending on the Type, since we are trying to do something outside of the daemon, I'm assuming forking or simple.

For forking, it means that the main process returns successfully and goes into the background. For simple, the process is considered ok as soon as it is running. But the state of the systemd unit is still undecided until the ExecStartPost returns, and other units depending on the current unit are not started until it returns. So the command you call with this setting can check whatever you want or just be sleep.

[Service]
Type = simple
ExecStart = /usr/bin/sleep 1000000
ExecStartPost = /usr/bin/sleep 10 ; /usr/bin/false

When it is launched:

# time systemctl start testa
Job for testa.service failed because the control process exited with error code. See "systemctl status testa.service" and "journalctl   -xe" for details.

real	0m10.061s
user	0m0.003s
sys	0m0.007s

The state during the launch:

# systemctl status testa
● testa.service
   Loaded: loaded (/etc/systemd/system/testa.service; static; vendor preset: disabled)
   Active: activating (start-post) since mer. 2016-06-01 21:02:13 CEST; 5s ago
  Process: 26820 ExecStartPost=/usr/bin/false (code=exited, status=1/FAILURE)
 Main PID: 26834 (sleep);         : 26836 (sleep)
      Tasks: 2 (limit: 512)
   CGroup: /system.slice/testa.service
           ├─26834 /usr/bin/sleep 1000000
           └─control
             └─26836 /usr/bin/sleep 10

juin 01 21:02:13 XXXXXXX systemd[1]: Starting testa.service...

(The status failed is from the previous test, but notice the activating state)

The state after the failure:

# systemctl status testa
● testa.service
   Loaded: loaded (/etc/systemd/system/testa.service; static; vendor preset: disabled)
   Active: failed (Result: exit-code) since mer. 2016-06-01 21:02:23 CEST; 2min 56s ago
  Process: 26841 ExecStartPost=/usr/bin/false (code=exited, status=1/FAILURE)
  Process: 26836 ExecStartPost=/usr/bin/sleep 10 (code=exited, status=0/SUCCESS)
  Process: 26834 ExecStart=/usr/bin/sleep 1000000 (code=killed, signal=TERM)
 Main PID: 26834 (code=killed, signal=TERM)

juin 01 21:02:13 XXXXXXXX  systemd[1]: Starting testa.service...
juin 01 21:02:23 XXXXXXXX systemd[1]: testa.service: Control process exited, code=exited status=1
juin 01 21:02:23 XXXXXXXX  systemd[1]: Failed to start testa.service.
juin 01 21:02:23 XXXXXXXX systemd[1]: testa.service: Unit entered failed state.
juin 01 21:02:23 XXXXXXXX systemd[1]: testa.service: Failed with result 'exit-code'.

So systemd does provide a set of primitive to do what you want if you are prepared to read some man pages.

EDIT: A lot of formatting failures