Question

I need to start “a.out” at a specific date/time.
for example, I want to start “a.out” at 12:10:30 PM very exactly.
Any Idea is appreciated !

Answer 1

That’s what cron and/or at are for.

Since cron only has a one minute resolution, you may want to set up a script that runs at 12:09.

This script would then go into a tight loop checking the date and time until it was exactly 12:10:30, then run your “real” code.

So, your cron entry would be:

9 12 * * * /mydir/myscript

and /mydir/myscript would be something like:

#!/bin/bash
while [[ $(date +%H%M%S) -lt 121030 ; do
    sleep 1
done
/mydir/myexecutable

That’s if you want it running many days at the same time of day. For a one-shot execution, you can still use the script, but use at to run it (the time string is YYYYMMDDhhmm):

at -f /mydir/myscript -t 201212311209

Alternatively, if your at is advanced enough, it may allow sub-minute specification in the -t option so that your wrapper job is not hanging around too long (time string of YYYYMMDDhhmm.ss):

at -f /mydir/myscript -t 201212311210.25