07-01-2008, 02:00 AM
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 Re: How to get an "alert" when a process dies
On Jul 1, 2:16*am, Robert Nichols wrote:
> In article <486902DF.3040...@gmail.com>,
> Nico Kadel-Garcia * wrote::Robert Nichols wrote:
>
> :> In article ,
> :> nicc777 * wrote:
> :> :Hi all,
> :> :
> :> :Even though I use Linux a lot, I have not been doing a lot of hard
> :> :core Linux sysadmin stuff for some time, hence the question here :-)
> :> :
> :> :Is there a way to trigger an event (like running a script) when a
> :>  rocess dies? Perhaps even a script to restart a process if it detects
> :> :that it's dead?
> :> :
> :> :I have been using cron for monitoring processes up to now, but the
> :> :monitoring interval is 1 minute apart. I have a project (streaming of
> :> :nature) that should not go down, but the problem is that sometimes it
> :> :dies and it takes up to a minute before the traditional monitoring
> :> :script will restart it.
> :> :
> :> :Any ideas?
> :>
> :> Can't you just run your process from a simple script that loops,
> :> restarting your process whenever it terminates:
> :>
> :> * * * *while :
> :> * * * *do
> :> * * * * * *myprocess [args ... ]
> :> * * * *done
> :>
> :> Alternatively, if this process is one that you want to start when the
> :> system boots then you could run it directly from /etc/inittab, using
> :> "respawn" in the action field. *If you do that, you'll probably want
> :> to invoke your process via 'su' or else it will be running with root
> :> privileges.
> :>
> :
> :Put a pause in there, of say a second, your script is going to hoover up
> :whatever CPU is available for itself.
>
> Curious. *I've got a couple of scripts that basically look like that,
> and the shell obediently waits, consuming no CPU whatever. *It will use
> CPU time only if 'myprocess' keeps terminating immediately. *And, if
> that process is as vital as the OP suggests, having a shell sitting in a
> loop trying to restart it isn't a big problem, though flooding some log
> file with error messages could indeed be nasty.
>
> Anyway, my suggestion wasn't really intended as a complete solution.
> For bulletproofing, you'd want to check whether the program you are
> trying to invoke exists and is executable, and limit the restart
> rate if it keeps dying immediately. *Something like:
>
> * * #!/bin/bash
> * * PROG=/bin/true
> * * N=0
> * * while :
> * * do
> * * * * if [ ! -x $PROG ]; then
> * * * * * * echo "$PROG is not executable" >&2
> * * * * * * exit 1
> * * * * fi
> * * * * if [ $N -lt $SECONDS ]; then
> * * * * * * N=$SECONDS
> * * * * elif [ $(($N - 5)) -ge $SECONDS ]; then
> * * * * * * echo "$PROG restarting too frequently -- sleeping">&2
> * * * * * * sleep 60
> * * * * fi
> * * * * N=$(($N+1))
> * * * * $PROG [args ... ]
> * * done
>
> --
> Bob Nichols * * * * AT comcast.net I am "RNichols42"
Ahh - this is excellent as well. Thanks a mil!
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