Ubuntu, upstart, and creating a pid for monitoring

Question

Below is a upstart script for redis. How to I create a pid so I use monit for monitoring?

#!upstart
description "Redis Server"

env USER=redis

start on startup
stop on shutdown

respawn

exec sudo -u $USER sh -c "/usr/local/bin/redis-server /etc/redis/redis.conf 2>&1 >> /var/log/redis/redis.log"

Answer 1

If start-stop-daemon is available on your machine, I would highly recommend using it to launch your process. start-stop-daemon will handle launching the process as an unprivileged user without forking from sudo or su (recommended in the upstart cookbook) AND it also has built in support for pid file management. Eg:

/etc/init/app_name.conf

#!upstart
description "Redis Server"

env USER=redis

start on startup
stop on shutdown

respawn

exec start-stop-daemon --start --make-pidfile --pidfile /var/run/app_name.pid --chuid $USER --exec /usr/local/bin/redis-server /etc/redis/redis.conf >> /var/log/redis/redis.log 2>&1

Alternatively you could manually manage the pid file by using the post-start script stanza to create it and post-stop script stanza to delete it. Eg:

/etc/init/app_name.conf

#!upstart
description "Redis Server"

env USER=redis

start on startup
stop on shutdown

respawn

exec sudo -u $USER sh -c "/usr/local/bin/redis-server /etc/redis/redis.conf 2>&1 >> /var/log/redis/redis.log"

post-start script
    PID=`status app_name | egrep -oi '([0-9]+)$' | head -n1`
    echo $PID > /var/run/app_name.pid
end script

post-stop script
    rm -f /var/run/app_name.pid
end script