Job Walltime Estimates

A job's walltime is another attribute that is helpful to inform PBS about. (Think of walltime as the time elapsed when watching the clock on the wall.) Setting a good walltime helps the scheduler assign jobs to nodes in an optimal fashion. By default, PBS assumes that a job will take one hour, unless you tell it otherwise.

This means that if you know that your job will take six hours, then you should certainly tell PBS, otherwise your job will be ended after an hour!

Accurately communicating your jobs' time requirements to PBS will allow PBS to allocate resources most effectively, and prevent your job from being prematurely terminated. Do not grossly overstate your wallclock requirement! Non-privileged jobs (with qos=1) are subject to a maximum wallclock limit of 600 hours per user.

You tell PBS your job's walltime with another -l directive:
#PBS -l walltime=4:00:00 # Set walltime to 4 hours

If you need to get an estimate of the walltime that your job will take, use the time command to get one:

time -p ./mycomputation
real 10:23
user 5:02
sys 3.63

Use the result from 'real' as an estimate for the computation's walltime. In this example, the walltime was 10:23, so requesting 12 minutes when running your production jobs is probably reasonable.