Why is --pidfilepath useful for mongod?

[Arkadiy]

mongod process already writes its pid to the lockfile, why is a separate pidfile needed? Is there any reason why giving e.g. start-stop-daemon the lockfile as --pidfile is not desirable?

[陆峰]

one reason I think is that you can put u MongoDB into /var/run directory and allows someone to write a script really easy to check if it is running and issue a plain kill command if one wants to end it. especially in distributed environment. 

在 2013年11月20日星期三UTC+8上午4时54分25秒，Arkadiy写道：

[Arkadiy]

But I can also check the mongod.lock file in the data dir (instead of /var/run) and stop it the same way, for example with 

start-stop-daemon --background --stop --pidfile /path/to/mongod.lock

You still need one lockfile per mongo process, etc.

I guess this could be useful if you had a standardized process manager/watchdog tool that would expect pids to live in /var/run, or didn't have access to the data dir?

[陆峰]

yes, u are right, I check the mongodb start script in Centos /etc/init.d/mongodb

start() {
        checkpath -d -m 0750 -o "${MONGODB_USER}":mongodb "${MONGODB_RUN}"


        # Listen to MONGODB_IP if configured
        [ -z "${MONGODB_IP}" ] || MONGODB_OPTIONS="--bind_ip ${MONGODB_IP} ${MONGODB_OPTIONS}"


        # Baselayout-1 user should use --chuid instead of --user
        local USEROPT="--user"
        if [ ! -f /etc/init.d/sysfs ]; then
                USEROPT="--chuid"
        fi


        ebegin "Starting ${SVCNAME}"
        start-stop-daemon --background --start --make-pidfile \
                --pidfile ${MONGODB_RUN:-/var/run/mongodb}/${SVCNAME}.pid \
                ${USEROPT} ${MONGODB_USER:-mongodb} \
                --exec ${MONGODB_EXEC:-/usr/bin/mongod} \
                -- \
                --port ${MONGODB_PORT:-27017} \
                --dbpath ${MONGODB_DATA:-/var/lib/mongodb} \
                --unixSocketPrefix ${MONGODB_RUN:-/var/run/mongodb} \
                --logappend --logpath /var/log/mongodb/${SVCNAME}.log \
                ${MONGODB_OPTIONS}
        eend $?
}


stop() {
        ebegin "Stopping ${SVCNAME}"
        start-stop-daemon --stop --pidfile ${MONGODB_RUN:-/var/run/mongodb}/${SVCNAME}.pid
        eend $?
}

it put all pid file input /var/run/mongodb

another reason is that if run many MonogDB daemons in one machine, you can put all pid into /var/run/mongodb, it is very easy for manage. 

在 2013年11月20日星期三UTC+8上午10时49分33秒，Arkadiy写道：

[Arkadiy]

The difference here is that the pidfile is generated by start-stop-daemon ( start-stop-daemon --background --start --make-pidfile ) and not by mongodb itself (--pidfilepath isn't passed). It seems you can use either approach to make the file (though not both together)

I'm asking because of an issue I encountered with a puppet deployment module here:

https://github.com/echocat/puppet-mongodb/pull/22