How is a multi-process job run in a single processor machine

[olgc]

Hi there,

When a job consists of several processes and is run in a single processor machine, how is it run? Are these processes run in parallel or one by one?

For example, these process are as following:

process1 -> process2 -> process3

How are they run: all three processes start at the same time and run in parallel or first process1 -> when it completes, process2 starts -> ...

Thanks,

[ray.wurlod]

The processes are in parallel, unless they are started in a fashion that makes one depend upon another.
This is completely handled by the operating system. Each is give a "time slice" - a short period during which it has use of the CPU, and other processes sleep. A process may relinquish its time slice voluntarily (for example to wait for an I/O operation to complete), or may exhaust its time slice.
Use the UNIX ps command to see all the processes running on the system.
DataStage processes are just some of these. Connected clients will have a dsapi_server process (and maybe a dsapi_slave process), running server jobs will have one or more uvsh processes, parallel jobs will have one or more osh processes, and there will be a couple more.

[kcbland]

poorly