Hide Daemons Behind Start Stop Scripts

As noted in UnixShellPatterns daemons need to be isolated from their terminals.

Forces

One problem with daemons is stopping them. Another is avoiding running two of them at one time. You also need to be able to stop and restart a daemon without thinking.

Solution A simple solution is

Make the daemon generate its own stop script.
Write a start script

You can use the data in the stop script to test whether the daemon is still running.

Example I run a simple Mailing list for students in some of my classes. For historical reasons it is called 'bbs'. Once upon a time The crontab was a bit disfunctional on the system so I used a daemon was called


        bbs.daemon

I would leave it running, sorting my Email, and redistributing it to other people in the class:


        : script of daemon that sorts bbs messages

        echo kill -9 $$ > /u/faculty/dick/bin/stop.bbs

        while sleep 30

        do

        /u/faculty/dick/bin/post.bbs

        done

When I run start.bbs the script checks to see if the daemon is already running, and if not spawns the deamon:


        : script to start an agent that proceses personal and BBS mail

        cd $HOME

        default=180

        if /u/faculty/dick/bin/psg bbs|egrep bbs.daemon

        then

        echo is already running

        /u/faculty/dick/bin/psg bbs|egrep bbs.daemon|awk '{print $2}'|

        sed 's/^/kill -9 /' > /u/faculty/dick/bin/stop.bbs

        exit 1

        fi

        pwd

        echo Starting Bulletin Board with delay ${1:-$default} seconds....

        cat /dev/null >nohup.out

        nohup nice bbs.daemon ${1:-$default} &

        sleep 1; echo

(psg is another script that does a PS and a Grep).

--DickBotting

any comments?

I've seen a somewhat different approach (Linux's gpm mouse daemon), where the program is written so that it check for an instance of itself running, and if found, exits, unless invoked with a specific argument (-k), where if there is another running copy, kills that copy before exiting. --PeteHardie

CategoryUnixShellPattern