RedHat daemon function usage

linux bash daemon redhat init
quickshiftin picture quickshiftin · Feb 13, 2014 · Viewed 29.1k times · Source

I'm working on an init script for Jetty on RHEL. Trying to use the daemon function provided by the init library (/etc/rc.d/init.d/functions).

I found this terse documentation, and an online example (I've also been looking at other init scripts on the system for examples).

Look at this snippet from online to start the daemon

daemon --user="$DAEMON_USER" --pidfile="$PIDFILE" "$DAEMON $DAEMON_ARGS &"
RETVAL=$?
pid=`ps -A | grep $NAME | cut -d" " -f2`
pid=`echo $pid | cut -d" " -f2`
if [ -n "$pid" ]; then
        echo $pid > "$PIDFILE"
fi

Why bother looking up the $PID and writing it to the $PIDFILE by hand? I guess I'm wondering what the point of the --pidfile option to the daemon function is.

Answer

jnas picture jnas · Jan 23, 2015

To answer the question you guess that you have, is that --pidfile is used to check whether the daemon process is already running. On RHEL (and derivates) the daemon function won't write the pidfile.

In the case that the program stays in the foreground it has to be explicitly sent to the background by appending & to the command and the pid has to be fetched afterwards. $! is not usable when using daemon.

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