Erik wrote:
> I was wondering if anyone knew a way to allow a shell
> command to run for a specific period of time. In this
> particular case, I want tcpdump to run for 23 hours,
> 59 minutes, 59 seconds.
It would be best if the process could limit itself, since anything you do in a shell script will have sloppy timing, maybe a few seconds off. But you can do this for any process, using the following crude approach within a single script:
This script should be run with all its output redirected to a log file, so you can have a record of how it went.
Run your process (tcpdump) in the background with &
This becomes an independent process, so the next command in your script will start immediately:
date # output goes into your log file.
sleep 86399 # Or less, since kill won't be instantaneous
date
Use a pipeline with "ps -ef" and "grep" to identify the running tcpdump process. Extract the pid using "cut" and do a "kill".
sleep 2 # just to give kill time to take effect
ps -ef | grep ... # Did it go away?
date
exit
Details on request, but the above commands are good things to learn. This type of ps + grep pipeline is also useful to detect if a duplicate copy of a script is running, etc.
The sleep command is only precise to within a second or two, and other system activity might delay the next command.
Vic
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