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Interactive use of the cluster can take place on the head/login node, but since this node is shared by all users and also supports some of the system administrative activities on the cluster, interactive use requiring significant CPU time (more than 1 hour) or memory (more than 10GB) should take place on a compute node.

Interactive Jobs

An interactive batch job is a process that allows a user to get interactive, command line access to a compute node or nodes. Interactive batch jobs use the same syntax as regular batch jobs, but no job script is specified. Slurm allows for different ways to access compute nodes interactively. The following command requests an interactive batch job with the default parameters for all resource requests (1 hour of run time on 1 processor):

/usr/bin/salloc --x11

Environment variables defined in the terminal where the request is submitted will automatically be transferred to the interactive node(s).  To request a longer run time or additional nodes, add specific resource requests:

/usr/bin/salloc -t 0:30:00 -N 1 --tasks-per-node=12 --x11

The above requests one interactive node and 12 compute cores on that node for half an hour.

Additional options to salloc can be seen by typing:

/usr/bin/salloc --help

The big memory nodes can be accessed by typing:

/usr/bin/salloc -p bigmem --x11

The GPU nodes can be accessed by typing:

/usr/bin/salloc -p gpu --x11  

When an interactive batch job is submitted, it is evaluated by the scheduling system to determine if the requested resources are available. The user will see output similar to:

salloc: Pending job allocation 162

salloc: job 162 queued and waiting for resources 

When a node becomes available and the jobs starts, the user’s command prompt will change to uniqueID@mualhpcp<n>, n is the allocated node’s number. When you have finished working on the compute node, type exit to end the job and return to the login node. The interactive job will automatically end once the requested time has elapsed.

If no nodes are available, the command will wait until a node becomes available. If you want to stop waiting and abandon your job request, use the Control-x-c key combination to terminate the job or type

scancel <jobid>

in a different terminal.