Cannot get systemd to restart a service if it crashes

I searched online and posted here to understand how to use systemd to auto start a c++ application, now I want it to automatically restart that application if it crashes.

I know the correct course of action is to make the application not crash, but it is not my program to change

Here is what I gathered so far from here:

and here:Writing a systemd script that starts 2 applications in linux

Create the file in /etc/systemd/system/app1.service with:

[Unit]
Description=app1 systemd service.
[Service]
Type=simple
ExecStart=/home/pi/app1
RemainAfterExit=no
Restart=on-failure
RestartSec=5s
[Install]
WantedBy=multi-user.target

Then execute to enable service

sudo systemctl enable app1.service

The service starts up initially, but when I execute

sudo kill xx where xx is the pid of the app, it does not restart itself

How can I fix this init.d script to automatically restart the app if it crashes?

Or is it not going to work if I kill it though sudo kill? In this case how can I test that it works without waiting for it to crash?

thanks

2 Answers

This is what Restart=on-failure does [emphasis mine]:

Restart=

Configures whether the service shall be restarted when the service process exits, is killed, or a timeout is reached. […]

Takes one of no, on-success, on-failure, on-abnormal, on-watchdog, on-abort, or always. […] In this context, a clean exit means an exit code of 0, or one of the signals SIGHUP, SIGINT, SIGTERM or SIGPIPE, and additionally, exit statuses and signals specified in SuccessExitStatus=. If set to on-failure, the service will be restarted when the process exits with a non-zero exit code, is terminated by a signal (including on core dump, but excluding the aforementioned four signals), when an operation (such as service reload) times out, and when the configured watchdog timeout is triggered.

^(source)

kill sends SIGTERM by default. That's why the service does not restart itself after you kill it.

How can I fix this script to automatically restart the app if it crashes?

If the app returns non-zero exit status in such situation then there's nothing to fix. The service will be restarted.

how can I test that it works without waiting for it to crash?

1. Kill it with SIGQUIT or SIGKILL:

   kill -s SIGQUIT $pid

2. Or you can use RestartForceExitStatus=SIGTERM to make the service restart itself after SIGTERM. But note kill $pid will then test if RestartForceExitStatus= works, not exactly Restart=.

3. Or you can (temporarily) modify /home/pi/app1 so it exits with a non-zero exit status after receiving SIGUSR1 or after few seconds. Send SIGUSR1 to the process or just wait, then poll systemctl status app1.service to see what happens.

Easy fix

It needed the forking type and the pid file, this will work with the sudo kill command Thanks,

[Unit]
Description=app1 systemd service.
[Service]
Type=simple
ExecStart=/home/pi/fbcp-ili9341
RemainAfterExit=no
Restart=always
RestartSec=5s
[Install]
WantedBy=multi-user.target