qlogin
The simplest thing you can do with the cluster is to just log in to the TUKEY
node and run things on it interactively. Once you’re logged in, it is just
being logged in remotely to any other computer. However, logging in must be
accomplished through the scheduler to balance requests for interactive and
non-interactive sessions and to send requests to the proper queues. To set up
an interactive session, use qlogin:
qlogin -q TUKEY
The -q TUKEY option specifies that you would like to log in to the TUKEY node.
You can, of course, try to log in interactively to a different node with -q
UI, if one is available, or use -q all.q to log in with the understanding
that you will get logged off if someone wants their node back.
IMPORTANT: By default, the above command will allocate all of the
available processors on TUKEY to your qlogin request (up to a maximum
of 16). In other words, no one else will be able to use TUKEY until you log
out (which you would do by typing exit or Ctrl+D). This is particularly bad
if you only need a small number of processors, or if you intend to stay logged
in for a long period of time (or both). To request an interactive session that
uses only, say, 4 processors, submit:
qlogin -q TUKEY -pe smp 4
The -pe option specifies the parallel environment you wish to have for your
qlogin session. There are various options, the differences between which get
rather technical, but the simplest is SMP (symmetric multiprocessing).
From here, you can do anything you would normally do at a terminal – run commands, run an interactive R session, etc. There are three primary reasons one might be interested in doing this:
- Your own computer has insufficient computational resources to run the interactive R session you have in mind.
- You need to set something up on the cluster, but don’t want to tie up a login node.
- You want to make sure a job will run on Neon or troubleshoot why it isn’t running (it can be difficult to do this non-interactively).
It is worth noting that qlogin respects X11 forwarding, so if you log in using
ssh -X or ssh -Y, or you are using NoMachine, you can do things like view
plots in R that are created on the compute node.
AGAIN: Try not to overuse qlogin by staying logged in for long periods of time or requesting far more slots than you are actually going to use. This ties up resources that other people may be trying to use.