I am learning and have some questions about using PBS to submit jobs in a cluster.
(1) If a job is parallelized by MPI and run by mpirun without using qsub, it cab be running on different nodes. So what is the point of using qsub?
Is the job not submitted by qsub queued or not?
(2) In a pbs script that is submitted by qsub, are all the commands executed one after the other?
If I want to run several executables at the same time, is it to make these calls background by adding "&" at the end?
(3) In the pbs script, if the several calls to run the executables are running the same time by running background, are the number of nodes and processors per nodes specified to be the total needed by all those calls?
If yes, and the number of nodes and processors per nodes specified are not completely available but enough to run some of the calls, will some of these calls be run first or delayed until the requested total resources are completely available?
For you better understanding my questions above, Our cluster is a linux cluster with Torque and Maui. I am reading tutorials online and find that the compilation is only on the head node, and after submitting the job by qsub, the other nodes are running the executable compiled on the head node. So that is why my questions arise.