Defining the Process Owner For Prologs & Epilogs

I've been working in the Grid Engine team for over five years ago, and I'm still learning about features of the product that I never knew about. One more was just brought to my attention.

When configuring a queue in Grid Engine, you can configure a prolog and epilog. The prolog is a script or binary that is run by the shepherd before running a job. The epilog is the same, except that it comes after a job finishes. When you set the prolog and epilog for a queue, all jobs that run in that queue inherit that prolog and epilog. (A job cannot specify its own prolog and epilog, but look for that to change in a future release. (Actually, if you configure your queue's prolog and epilog to read a custom environment variable in the job's environment and exec the path it contains, you can effectively allow a job to specify its own prolog and epilog by setting them in the environment variables.))

The epilog and prolog are well known tools. What I never noticed, though, is that not only can you specify a path, but you can also specify the user as whom the prolog or epilog should run. For example, if you set the queue's prolog to root@/path/to/my/prolog, the shepherd will execute the prolog as root, no matter who submitted the job. This is really helpful if your prolog and/or epilog needs to do something that has restricted access, such as mounting a directory or modifying the grid configuration. Because only the administrator can change the queue configuration, this feature is not a big security risk. (Actually, this feature is a compelling reason for restricting who has manager rights on your grid. Anyone who is recognized as a grid manager could change a queue to run a malicious prolog/epilog as root, submit a job to that queue, and compromise the system.)

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