Shell Script to find out if a process is running on any all machines Post: 302770061

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Top Forums Shell Programming and Scripting Shell Script to find out if a process is running on any all machines Post 302770061 by Corona688 on Thursday 14th of February 2013 10:34:24 AM

02-14-2013

Registered User

Lock file is a bit of a misnomer here, since it doesn't lock anything. This is what's usually called a PID file. They often belong in /var/run.

Don't bother with ps | grep | awk | sed | cut | kitchen | sink games to check the name. That's not reliable and not portable, one oddly named process will break it, strange systems won't like it. If the PID file and the PID itself exist, trust it.

What's your system? If you're on a system that has /proc/, like Linux, that makes things a bit simpler.

If the script you're launching would be able to create and delete its own PID file, that would make it even more reliable.

I wrote this init script(some task-specific stuff stripped out) a little while ago:

Code:

#!/bin/bash

PIDFILE="/var/run/whatever.pid"

start() {
        # If PID file exists, it can be read, the contents aren't blank, and the process still exists,
        # it's already running.
        if [ -f $PIDFILE ] && read PID < $PIDFILE && [ ! -z "$PID" ] && [ -d /proc/$PID ]
        then
                echo "Already started" >&2
                exit 0
        fi

        echo "starting whatever..." >&2
        nohup whatever & disown
        echo "$!" > $PIDFILE
        echo "started whatever" >&2
}

stop() {
        if [ -f $PIDFILE ] && read PID < $PIDFILE && [ ! -z "$PID" ] && [ -d /proc/$PID ]
        then
                echo "stopping whatever"
                # Give it a polite SIGINT
                kill -INT $PID
                sleep 1

                # If it doesn't die, give it higher signals until it does
                for SIG in QUIT TERM 9
                do
                        [ -d /proc/$PID ] || break
                        kill -$SIG $PID
                        sleep 2
                done

                if [ -d /proc/$PID ]
                then
                        echo "Couldn't stop whatever" >&2
                        return 1
                fi

                echo "stopped whatever" >&2
                return 0
        else
                echo "whatever not started" >&2
                exit 1
        fi
}

case "$1" in
start)  start   ;;
stop)   stop    ;;
*)       echo "unknown option" >&2 ; false ;;
esac

exit $?

I use it to start and stop a micro HTTP server. The script should work in any Bourne shell that has functions, including bash, ksh, dash, and busybox ash. If it complains about 'disown', remove it, some shells don't need that.

Last edited by Corona688; 02-14-2013 at 11:42 AM..

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LEARN ABOUT REDHAT

pidof

PIDOF(8)						Linux System Administrator's Manual						  PIDOF(8)

NAME

       pidof -- find the process ID of a running program.

SYNOPSIS

       pidof [-s] [-x] [-o omitpid] [-o omitpid..]  program [program..]

DESCRIPTION

       Pidof  finds  the  process  id's (pids) of the named programs. It prints those id's on the standard output. This program is on some systems
       used in run-level change scripts, especially when the system has a System-V like rc structure. In that case these scripts  are  located	in
       /etc/rc?.d, where ? is the runlevel. If the system has a start-stop-daemon (8) program that should be used instead.

OPTIONS

       -s     Single shot - this instructs the program to only return one pid.

       -x     Scripts too - this causes the program to also return process id's of shells running the named scripts.

       -o     Tells  pidof  to omit processes with that process id. The special pid %PPID can be used to name the parent process of the pidof pro-
	      gram, in other words the calling shell or shell script.

NOTES

       pidof is simply a (symbolic) link to the killall5 program, which should also be located in /sbin.

       When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is  possible  that
       it returns pids of running programs that happen to have the same name as the program you're after but are actually other programs.

SEE ALSO

       shutdown(8), init(8), halt(8), reboot(8)

AUTHOR

       Miquel van Smoorenburg, miquels@cistron.nl

								    01 Sep 1998 							  PIDOF(8)

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