What is qrsh

Both methods have a default wallclock limit of 12 hours which users may override. Many options available to the qsub command can be used with qsh and qrsh commands. For graphics and GUI-based applications, qsh delivers better performance than qrsh. The session invoked with qrsh command will start in your current window and, as such, does not require x-forwarding.

But, if x-forwarding is enabled, you can start graphics applications within the session. The above command requests exclusive access to one processor on one of the compute nodes with a default hour wall time. This time allotment is more than adequate for most interactive batch jobs. If you need to request a longer time or other additional resources, you can add necessary options.

For example, to request an interactive session with 4 processors for 24 hours:. The job is rejected if no appropriate resources are available. Instead, qrsh assumes that the job is embedded in a parallel job that already has allocated suitable resources on the designated remote execution host. This form of qrsh is commonly used in qmake and in a tight parallel environment integration. The default is not to inherit external job resources. Instead, you execute the command without the wrapping shell.

Use this option to speed up execution, as some overhead, such as the shell startup and the sourcing of shell resource files, is avoided. For an interactive session, you reserve some compute nodes via the scheduler and then are logged in live, just like on the login nodes. These can be used for live visualisation, software debugging, or to work up a script to run your program without having to submit each attempt separately to the queue and wait for it to complete.

Please note that time limits are restricted to two hours for interactive sessions, and available core counts are limited. Interactive sessions are requested using the qrsh command. It typically takes the form:. In this example you are asking to run eight parallel processes within an MPI environment, MB RAM per process, for a period of two hours the maximum allowed for interactive sessions.