Problems: When I submit more than two script jobs through "Torque PBS", all the jobs always use the same nodes (although these nodes has been occupied and other nodes are free).

Descriptions:

I write a script to use Forcite module to run NPT dynamics. I execute this script in standalone mode on linux culster. This script is submitted through Torque PBS by the PBS file as follows:

   aaa.pbs

#!/bin/bash

#PBS -N myjob2

#PBS -j oe

#PBS -l nodes=1:ppn=8

#PBS -l cput=9000000000

cd /home/huhaixiang/ms-computation/sw8

RunMatServer.sh -np 8 swelling-standalone    # the script file is swelling-standalone.pl

///////////////////////////////////////////////////////////////////file end/////////////////

the machines.LINUX in ms installation directory is

cu01:8

cu02:8  

cu03:8

cu04:8

cu05:8

cu06:8

Then I submit one job by command "qsub aaa.pbs" on linux. This job runs successfully on node cu01. If I submit the second job at the same time, this second job can run also. But the second job also runs on the node cu01 althought the othe nodes are free. Could you please tell me why this happen? How can job be executed on the occupied nodes?