Ttyjfyk

I'm trying to create startup / shutdown script for my application, but I do not have experience with that, so I wanted to start with screen (I'll refer to it as "test_screen").

Firstly I thought I'll create script in /etc/init.d only. And I got inspiration from here - https://unix.stackexchange.com/a/20361/29677 .

Basic idea to simuate my appplication is to use

• 
  screen -d -m -S test_screen to startup


• 
  screen -S test_screen -X quit for shutdown


• and screen –list for status (kind of)

But when I tried /etc/init.d/test_screen start I got

Reloading systemd: [ OK ]
Starting test_screen (via systemctl): Failed to start test_screen.service: Unit not found.
 [FAILED]

So it seems I have to create unit.

I tried with https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/sect-Managing_Services_with_systemd-Unit_Files.html , so I have my unit file in /etc/systemd/system:

# cat test_screen.service
[Unit]
Description=Testing `screen` service

[Service]
Type=simple
ExecStart=/bin/screen -d -m -S test_screen
ExecStop=/bin/screen -S test_screen -X quit
Environment=
Restart=always

[Install]
WantedBy=default.target

First question is, should I have /etc/init.d/test_screen start as ExecStart or not? Definitely it won't be one liner...

Anyway, it is not running. In /var/log/messages I see

Sep 19 10:54:58 somehostname systemd: Started Testing `screen` service.
Sep 19 10:54:58 somehostname systemd: Starting Testing `screen` service...
Sep 19 10:54:58 somehostname systemd: test_screen.service holdoff time over, scheduling restart.
Sep 19 10:54:58 somehostname systemd: Started Testing `screen` service.
Sep 19 10:54:58 somehostname systemd: Starting Testing `screen` service...
Sep 19 10:54:58 somehostname systemd: test_screen.service holdoff time over, scheduling restart.
Sep 19 10:54:58 somehostname systemd: Started Testing `screen` service.
Sep 19 10:54:58 somehostname systemd: Starting Testing `screen` service...
Sep 19 10:54:59 somehostname systemd: test_screen.service holdoff time over, scheduling restart.
Sep 19 10:54:59 somehostname systemd: Started Testing `screen` service.
Sep 19 10:54:59 somehostname systemd: Starting Testing `screen` service...
Sep 19 10:54:59 somehostname systemd: test_screen.service holdoff time over, scheduling restart.
Sep 19 10:54:59 somehostname systemd: Started Testing `screen` service.
Sep 19 10:54:59 somehostname systemd: Starting Testing `screen` service...
Sep 19 10:54:59 somehostname systemd: test_screen.service holdoff time over, scheduling restart.
Sep 19 10:54:59 somehostname systemd: start request repeated too quickly for test_screen.service
Sep 19 10:54:59 somehostname systemd: Failed to start Testing `screen` service.
Sep 19 10:54:59 somehostname systemd: Unit test_screen.service entered failed state.
Sep 19 10:54:59 somehostname systemd: test_screen.service failed.

How can I find the reason, why it is entering failed state? All suggestions are welcome.

It seems, that I solved it for screen...

Firstly I removed that Restart=always parameter.

To make it work I also had to add RemainAfterExit=True.

With old init scripts it was clear where to have the code. I do not really know what is a proper place to put the rest of code. Should I simply call my script from ExecStart=?

My additional findings during learning.

status

There is a good question (I meant I was interested too), how to implement status checking - systemd custom status message?

Short answer is, it works (somehow) out f the box = you do not need to care much.

So, for my test_screen service I can call systemctl status test_screen.service and I'll get

● test_screen.service - Testing `screen` service
 Loaded: loaded (/etc/systemd/system/test_screen.service; disabled; vendor preset: disabled)
 Active: active (running) since Wed 2017-09-20 12:48:34 CEST; 1s ago
 Process: 36633 ExecStart=/bin/screen -d -m -S test_screen (code=exited, status=0/SUCCESS)
 Main PID: 36634 (screen)
 CGroup: /system.slice/test_screen.service
 ├─36634 /bin/SCREEN -d -m -S test_screen
 └─36635 /bin/sh

Sep 20 12:48:34 somehostname systemd[1]: Starting Testing `screen` service...
Sep 20 12:48:34 somehostname systemd[1]: Started Testing `screen` service.

...strange is, that when I stop it, for status I got failed:

● test_screen.service - Testing `screen` service
 Loaded: loaded (/etc/systemd/system/test_screen.service; disabled; vendor preset: disabled)
 Active: failed (Result: exit-code) since Wed 2017-09-20 12:51:00 CEST; 1s ago
 Process: 36805 ExecStop=/bin/screen -S test_screen -X quit (code=exited, status=0/SUCCESS)
 Process: 36633 ExecStart=/bin/screen -d -m -S test_screen (code=exited, status=0/SUCCESS)
 Main PID: 36634 (code=exited, status=1/FAILURE)

Sep 20 12:48:34 somehostname systemd[1]: Starting Testing `screen` service...
Sep 20 12:48:34 somehostname systemd[1]: Started Testing `screen` service.
Sep 20 12:51:00 somehostname systemd[1]: Stopping Testing `screen` service...
Sep 20 12:51:00 somehostname systemd[1]: test_screen.service: main process exited, code=exited, status=1/FAILURE
Sep 20 12:51:00 somehostname systemd[1]: Stopped Testing `screen` service.
Sep 20 12:51:00 somehostname systemd[1]: Unit test_screen.service entered failed state.
Sep 20 12:51:00 somehostname systemd[1]: test_screen.service failed.

to overcome that I had to have RemainAfterExit=True (because I tried the suggestion to have Type=forking and I commented out that RemainAfterExit option).

list-unit-files

I had an issue, that I'm not able to reproduce now - when I tried systemctl start the response was something like "No unit file", so I was wondering if there is a need to register it somehow.

No, you do not need to. You can execute systemctl list-unit-files --type=service and you should see your unit there. My problem was, that ExecStart parameter was wrong. When I tried the same now I have easier to understand message:

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

$ systemctl status test_screen.service
● test_screen.service - Testing `screen` service
 Loaded: loaded (/etc/systemd/system/test_screen.service; disabled; vendor preset: disabled)
 Active: failed (Result: exit-code) since Wed 2017-09-20 12:55:53 CEST; 1min 3s ago
 Process: 37344 ExecStart=/bin/screen2 -d -m -S test_screen (code=exited, status=203/EXEC)
 Main PID: 36634 (code=exited, status=1/FAILURE)

Sep 20 12:55:53 somehostname systemd[1]: Starting Testing `screen` service...
Sep 20 12:55:53 somehostname systemd[37344]: Failed at step EXEC spawning /bin/screen2: No such file or directory
Sep 20 12:55:53 somehostname systemd[1]: test_screen.service: control process exited, code=exited status=203
Sep 20 12:55:53 somehostname systemd[1]: Failed to start Testing `screen` service.
Sep 20 12:55:53 somehostname systemd[1]: Unit test_screen.service entered failed state.
Sep 20 12:55:53 somehostname systemd[1]: test_screen.service failed.

Executing script

I tried to modify my test_screen to call script

$ cat /etc/systemd/system/test_screen_script.service
[Unit]
Description=Testing `screen` service

[Service]
Type=forking
ExecStart=/root/test_screen_start.sh
ExecStop=/root/test_screen_stop.sh
#Environment=
#Restart=always
RemainAfterExit=True

[Install]
WantedBy=default.target

while scripts are just wrapped for previous calls

$ cat /root/test_screen_start.sh
/bin/screen -d -m -S test_screen
$ cat /root/test_screen_stop.sh
/bin/screen -S test_screen -X quit

when I did that, it is not starting up:

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

$ systemctl status test_screen_script.service
● test_screen_script.service - Testing `screen` service
 Loaded: loaded (/etc/systemd/system/test_screen_script.service; disabled; vendor preset: disabled)
 Active: failed (Result: exit-code) since Wed 2017-09-20 15:47:59 CEST; 8s ago
 Process: 63582 ExecStart=/root/test_screen_start.sh (code=exited, status=203/EXEC)
 Main PID: 60698 (code=exited, status=0/SUCCESS)

Sep 20 15:47:59 somehostname systemd[1]: Starting Testing `screen` service...
Sep 20 15:47:59 somehostname systemd[63582]: Failed at step EXEC spawning /root/test_screen_start.sh: Exec format error
Sep 20 15:47:59 somehostname systemd[1]: test_screen_script.service: control process exited, code=exited status=203
Sep 20 15:47:59 somehostname systemd[1]: Failed to start Testing `screen` service.
Sep 20 15:47:59 somehostname systemd[1]: Unit test_screen_script.service entered failed state.
Sep 20 15:47:59 somehostname systemd[1]: test_screen_script.service failed.

It would be good is someone can describe the reason. Fix for that is to add #!/bin/bash.

References

• I found that list-unit-files here: https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units