Portable Batch System Processing

What is a PBS Job?

PBS Queue Policies

PBS Commands

Portable Batch System Processing

The Portable Batch System (PBS) is used to submit batch jobs. PBS allows you to:

• Specify system resource requirements for a job
• Control how the job will be processed
• Submit jobs across scheduled and unscheduled system shutdowns
• Monitor the progress of job execution
• Specify the location of output upon job completion
• Submit a batch job from a remote host

A PBS job (also called a request) is a sequence of shell commands--often referred to as the "job script"--that, when scheduled to run, executes within the resource constraints that are specified within the job script, on the command-line, or by system default. Standard output and standard error are redirected to files created by PBS. These files are returned when the job is finished. The qsub command is used to "submit" a job to PBS. Input to the qsub command (the shell commands) may be entered directly from the terminal or may be placed in a script file. (see Sample PBS Scripts" for some sample PBS job scripts) The qstat command with its many options are used to display queue status and list available queues respectively.

PBS Queue Policies

The batch queues are designed to provide the capability to process the particular mix of jobs run on this system. Entry into a regular queue is determined by the resources the job requests.   More specifically, the scheduler examines the job for user-specified limits on CPU time, memory, and or queue and then checks the batch queues in order from the lowest (most restrictive) to the highest (least restrictive) limits. The batch job is assigned to the first queue that can satisfy the resource requests (limits). If no limits are assigned to a request, the job will be submitted to the queue with the lowest limits.

When a batch job exceeds any of its limits (default or specified), job execution stops and any output obtained up to that point is returned. Therefore, when you submit a job, set realistic limits that will allow the job to complete in the proper queue, especially if the job requires large amounts of memory and/or CPU time. The method for determining the size of your job is discussed in Section - PBS Memory and Time Limits.

The primary purpose of the debug queue is for debugging purposes and compiles or other short activities that require more memory than can be obtained interactively. Using the debug queue simply to get faster turnaround is considered unfriendly behavior. Self-submitting jobs are strictly forbidden and when noticed will result in the job being deleted without warning.

See  Coding Programs for Manual Checkpointing for information on setting up checkpointing in your code.

Additional information on queue policies, including usage and charging is available in the General Information section on PBS Queue Policies.

PBS Commands

Three basic commands help make effective use of PBS. Table below summarizes these commands. These commands will be explained in detail in the following sections.

 PBS Commands