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I have an application (OS is Ubuntu 16.04) that basically open the camera do some stuff with the video stream. It's managed by a systemd service:

[Unit] Description=My Application After=network.target StartLimitInterval=0 [Service] Type=simple Restart=always RestartSec=5 User=myuser WorkingDirectory=/opt/foo/ ExecStart=/opt/foo/myapplication [Install] WantedBy=multi-user.target

Then I have a desktop entry that stop the service and re-run my application with an argument:

[Desktop Entry] Name=Myapp Type=Application Exec=/opt/foo/launcher.sh Terminal=true Path=/opt/foo/ Categories=None;

This is my launcher:

#!/bin/bash service myservice stop /opt/foo/myapplication --debug

This is working, anyway I canno find a way to restart the service when I close the application launched by the desktop entry. I tried to add a service restart at the end of the launcher but it doesn't work, because when I close the terminal in which the application run, everything I presume is killed. How can I do it?

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3 Answers 3

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You can write a unit file in, say, /etc/systemd/system/myprocess.service:

[Unit] Description=My Process [Service] ExecStart=/bin/myprocess Restart=always [Install] WantedBy=multi-user.target

And then in the desktop entry create a launcher to do

systemctl start myprocess.service

But remember not to enable that service in startup so can you start it manually from you executable entry.
EDIT:
If you also need to run in debug mode than create another service unit with the --debug parameter. You can create another desktop entry to point a script that look like(just representative idea)

systemctl stop myprocess.service // to stop previous service systemctl start processwithdebug.servce // to debug
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  • my application must run continuously, I need to sometimes to stop the service, open in debug mode and automatically restart the service when I close the application.. Commented Jul 3, 2020 at 8:06
  • Does edited answer helped? Commented Jul 3, 2020 at 8:14
  • what happen when I close my application in debug mode ? who is gonna restart the normal service in this way...? Commented Jul 3, 2020 at 13:16
  • to close you can again make the script which restart the previous service soon after the current one is closed Commented Jul 3, 2020 at 14:14
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You can have systemd do some of the work for you with a second unit B by saying that it Conflicts with the first unit A; then when you start B, it will stop A. Sadly, when B stops, A is not restarted by default, but you can add a OnFailure line; if B exits with a failure, A will be started. To ensure failure in case of normal exit of B you can use an ExecStop that sets the return code to non-zero.

A.service:

[Service] Type=simple ExecStart=/opt/foo/myapplication

B.service:

[Unit] Conflicts=A.service OnFailure=A.service [Service] Type=simple ExecStart=/opt/foo/myapplication --debug ExecStop=/usr/bin/false
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  • I need to see also the console output when I run in Debug mode.. in this way I guess I'm not able to automatically open a terminal with the output from my application.. Commented Jul 6, 2020 at 7:30
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You could use a lock file to ensure that only one instance of your application runs. Instead of systemctl stop myservice in your launcher, run systemctl restart myservice, and in the 5 seconds it needs to restart the application, start your debug version after acquiriing a lock file:

systemctl restart myservice flock /opt/foo/mylock /opt/foo/myapplication --debug

and change the unit file to use the same lock:

ExecStart=/usr/bin/flock /opt/foo/mylock /opt/foo/myapplication

It will restart after 5 seconds then wait to acquire the lock, and hold it whilst running the application. The lock file can be anywhere. You can actually use /opt/foo/myapplication as the lock file, but if you are recompiling it or something you will lose the lock when it changes.

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