Question

I have created an application that is basically a deamon written in C. It is stopped and started using a shell script. Specifically, to stop it, kill is used to send a SIGTERM signal. The PID of the daemon is stored in a file on the disc in the format:

1234\n

A user reports that they cannot stop the daemon, the shell script returns the error:

kill: `': not a pid or valid job spec

The PID is fetched and used in the shell script as follows:

if [ -f "${PID_FILE}" ]
then
    FCPID=`head -n 1 $PID_FILE`
    kill -n SIGTERM "${FCPID}"
    RETVAL=$?
    if [ $RETVAL -eq 0 ]
    then
        rm -f ${PID_FILE}
        echo "OK"
    else
        echo "FAIL"
        exit 1
    fi
else
    echo "Wasn't running"
    exit 1
fi

It works fine on my machine (Ubuntu 10.04) and so far no one else has reported this problem. Does anyone recognise the error or is there a mistake in the shell script that could cause problems on some platforms?

Answer 1

That error occurs when you pass kill an empty arg as a PID, i.e.

[me@home]$ kill -n SIGTERM ""
kill: `': not a pid or valid job spec

My guess is your script throws up that error when the PID_FILE exists but is empty, hence ${FCPID} ends up as an empty string.

Check that the start script is actually writing out the PID_FILE correctly on your user’s machine.