Setting number of threads using OpenMP

We can set either in the code or through environment variable. If we use environtment variable, we simply type
$ setenv OMP_NUM_THREADS 6
where 6 is the number of cpus we want to use.

failed to poll for a spawned proc

I am having problem running an openmpi program. It kept on giving me this error:
[opto023:31621] pls:tm: failed to poll for a spawned proc, return status = 17002
[opto023:31621] [0,0,0] ORTE_ERROR_LOG: In errno in file ../../../../../orte/mca/rmgr/urm/rmgr_urm.c at line 462
[opto023:31621] mpirun: spawn failed with errno=-11
I after I searched in the net, it might be due to OpenMPI and [...]