Okay, let us say we want to use a node interactively:
If you want to take advantage of Discovery while also using a graphical software (such as GaussView), you need to start by logging in with X11 forwarding:
$ ssh -X surname.f@discovery2.neu.edu
You can find more details about loading X11 here.
Remember how we do not want to do anything resource intensive on the log in nodes (discovery2 and discovery4)? Doing so would cause everyone difficulties, and ruffle some jimmies. Requesting an interactive job and logging in to a compute node is the solution.
First we need to request a compute node to use.
$ salloc -N 1 --exclusive -p ht-10g
salloc: Granted job allocation 649056
This will request exclusive use of a free node on partition ht-10g.
(It would make sense to check the queues before choosing a partition, for example sinfo | grep idle will show how many idle nodes are in each partition.
One of the ser-par-10g- partitions is usually a good bet.)
To find out which node you were allocated by Slurm:
$ squeue -u <username>
where is your username, eg. husky.id. For example, it will look like this:
JOBID PARTITION NAME USER ST TIME NODES NODELIST(REASON)
649056 ht-10g bash <username> R 0:08 1 compute-0-006
This tells us our job 649056 is running on node compute-0-006. Then log in to your shiny new compute node!
$ ssh -X compute-0-006
Sometimes, it may prompt you for a password. Just Ctrl-C and try to ssh -X <compute-node> again.
Now you're on an interactive session!
[<username>@compute-0-006 ~]$
For example, if I want to run GaussView (and have all the proper modules installed):
$ gview
(This is where you would find out that you need to use -Y instead of -X, but practice makes perfect!)
This is where you would do interactive python work eg. in ipython (see chapter 4).
Once you are done with your interactive session, log out of the compute node
by typing exit and then release the allocation using scancel <jobID>, e.g.:
r.west@compute-0-006 ~]$ exit
logout
Connection to compute-0-006 closed.
[r.west@discovery2 ~]$ scancel 649056
salloc: Job allocation 649056 has been revoked.
Hangup
[r.west@discovery2 ~]$
Next: 7. Submitting an array of jobs.