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

1. Make the daemon generate its own stop script.
2. 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

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any comments?

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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

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CategoryUnixShellPattern