I have searched around a bit for this and can't seem to find anything helpful.

I have my PC running Ubuntu 12.10 set up to suspend after 30 minutes of inactivity. I don't want to change that, it works great most of the time.

What I do want to do is disable the automatic suspend if a particular application is running. How can I do this?

The closest thing I've found so far is to add a shell script in /usr/lib/pm-utils/sleep.d which checks if the application is running and returns 1 to indicate that suspend should be prevented. But it looks like the system then gives up on suspending automatically, instead of trying again after another 30 minutes. (As far as I can tell, if I move the mouse, that restarts the timer again.) It's quite likely the application will finish after a couple of hours, and I'd rather my PC then suspended automatically if I'm not using it at that point. (So I don't want to add a call to pm-suspend when the application finishes.)

Is this possible? Any advice would be appreciated.

Cheers.

EDIT: As I noted in one of the comments below, what I actually wanted was to inhibit suspend when my PC was serving files over NFS; I just wanted to focus on the "suspend" part of the question because I already had an idea how to solve the NFS part. Using the 'xdotool' idea given in one of the answers, I have come up with the following script which I run from cron every few minutes. It's not ideal because it stops the screensaver kicking in as well, but it does work. I need to have a look at why 'caffeine' doesn't correctly re-enable suspend later on, then I could probably do better. Anyway, this does seem to work, so I'm including it here in case anyone else is interested.

#!/bin/bash

# If the output of this function changes between two successive runs of this
# script, we inhibit auto-suspend.
function check_activity()
{
    /usr/sbin/nfsstat --server --list
}

# Prevent the automatic suspend from kicking in. 
function inhibit_suspend()
{
    # Slightly jiggle the mouse pointer about; we do a small step and
    # reverse step to try to stop this being annoying to anyone using the
    # PC. TODO: This isn't ideal, apart from being a bit hacky it stops
    # the screensaver kicking in as well, when all we want is to stop
    # the PC suspending. Can 'caffeine' help?
    export DISPLAY=:0.0
    xdotool mousemove_relative --sync --  1  1
    xdotool mousemove_relative --sync -- -1 -1
}

LOG="$HOME/log/nfs-suspend-blocker.log"
ACTIVITYFILE1="$HOME/tmp/nfs-suspend-blocker.current"
ACTIVITYFILE2="$HOME/tmp/nfs-suspend-blocker.previous"

echo "Started run at $(date)" >> "$LOG"
if [ ! -f "$ACTIVITYFILE1" ]; then
    check_activity > "$ACTIVITYFILE1"
    exit 0;
fi

/bin/mv "$ACTIVITYFILE1" "$ACTIVITYFILE2"
check_activity > "$ACTIVITYFILE1"

if cmp --quiet "$ACTIVITYFILE1" "$ACTIVITYFILE2"; then
    echo "No activity detected since last run" >> "$LOG"
else
    echo "Activity detected since last run; inhibiting suspend" >> "$LOG"
    inhibit_suspend
fi