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I am still confused about systemd services being active vs the process still running vs not running etc.

Let's say I have the following basic shell script called my_script.sh :

#!/bin/sh
touch /my_dir/my_file.txt
echo "Hello from my_script.sh" >> /my_dir/my_file.txt

I have a system service called my_service.service which calls my_script.sh as follows :

[Unit]
Description=my service 

[Service]
Type=simple
ExecStart=sh /my_dir/my_script.sh
RemainAfterExit=yes
Restart=always

[Install]
WantedBy=multi-user.target

The fact that I have Restart=always , does this mean that as soon as my shell script finishes executing, it should execute again, and again, hence continuously writing to the file?

My understanding is that with Restart=always , the service is restarted regardless if there was a clean exit or not. This statement I don't understand properly. Will there be a clean exit after my_script.sh executes.

Now the line RemainAfterExit=yes , in my case, what is the effect of having this line defined or not?

Thanks in advance for clearing up any doubts.

  • The confusion might be because your script is not a service. A service continues to run after it is started. For example a listening service such as an SSH server. It runs in the background waiting for a service request. Your script doesn't do that. It runs and immediatly quits. When you think of 'restart' in the context of a service that is designed to run continuously, then it will probably make more sense to you. If a listening service such as SSH falls down then do we want to restart it or do we want to examine the reason for the crash? – Stephen Boston Jun 17 at 21:57
  • @StephenBoston In my case in my question, when my script finishes executing, should my service restart it ? I just can't seem to get this answer whatsoever – Engineer999 Jun 18 at 6:53
  • @StephenBoston In my case above, the script my_script.sh runs, then exits when finishes. However, the system service does not restart it again as I would expect having "Restart=always". This for me is confusing – Engineer999 Jun 18 at 7:27
  • Hm, I think I see now. Interesting. What happens if you put a long-running loop in your script, or set it to wait for input, something so that it continues to run. Then kill the process and see what happens. – Stephen Boston Jun 18 at 15:39
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This line RemainAfterExit=yes mean service showed as active when script in ExecStart ends with success exit code.

This line Restart=always mean restart on each of next events:

  • Clean exit code or signal
  • Unclean exit code
  • Unclean signal
  • Timeout
  • Watchdog

If you need to not restart service on some exit codes, check this option: RestartPreventExitStatus=

More information about systemd.service there is

  • "Clean exit code or signal" - Is a clean exit when the script executes to completion? , hence my script creates the file, then writes to it and then has nothing else to do . I just can't seem to understand this part – Engineer999 Jun 17 at 21:15
  • @Engineer999: Why don't you try it? Execute your script from the command line and check its exit status with echo $? - what do you get? I get 0 which means that the script exited normally. – NickD Jun 17 at 21:22
  • @NickD That's when I run my script by itself yes. So my service should be restarting the script continuously? because it is not. I just can't seem to get a straight answer here – Engineer999 Jun 17 at 21:43

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