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Kill process by pid file

Posted by: admin November 30, 2017 Leave a comment

Questions:

I try to kill a process by pid file:

kill -9 $(cat /var/run/myProcess.pid)

The pid file contains the process number. However executing the kill gives me no stdout and the processes is still alive. But this works:

kill -9 PID

What is wrong with the first kill command? Does it fail to extract the PID from the file?

Example content of pid file:

5424

and

kill -9 5424

works.

Answers:

I believe you are experiencing this because your default shell is dash (the debian almquist shell), but you are using bash syntax. You can specify bash in the shebang line with something like,

#!/usr/bin/env bash

Or, you could use the dash and bash compatible back-tick expression suggested by admdrew in the comments

kill -9 `cat /var/run/myProcess.pid`

Regardless, you can’t rely on /bin/sh to be bash.

Questions:
Answers:

In some situations, the more compact:

pkill -F /var/run/myProcess.pid

is the way to go. I’ve had trouble with the varieties:

kill $(cat /var/run/myProcess.pid)
# Or
kill `cat /var/run/myProcess.pid`

when I had to put the command into something else which might parse it using different rules, like Monit does for its start/stop commands.