Getting started with the JANUS supercomputer

Downloads

Welcome

This is a quick-start guide to the JANUS supercomputer at the University of Colorado Boulder. You will need terminal access in order to acccess JANUS.


Login

You will need to create an account and request an allocation in order to access and use JANUS. Please follow the steps in our Quick Start Guide. Once you have an account with a registerd OTP device, you can login.

$ ssh {username}@login.rc.colorado.edu

This will prompt you for you password, which is you PIN + the six-digit number from your OPT device. You are now on one of four login nodes: login01, login02, login03, login04.

Please do not run simulations on the login nodes.


Jobs

JANUS uses a scheduler to allow fair-sharing of the compute resources. From the login nodes, there are two ways for you to access compute nodes and run your code:

Both methods will use the `qsub` command. This command is available once you load the appropriate softare. In the terminal window, type:

$ module load torque
$ module load moab

Interactive Jobs

Now you are ready to create an interactive session on a compute node. To do this, you simply type:

$ qsub -I -q janus-debug

The -I stands for interactive. The -q janus-debug specifies the queue that you are requesting. For a full list of JANUS queues, please refer to our queue documentation.

This will eventually give you another command pompt, signifying that you are now on a computer resoure. To verify this, you can type hostname to see that you are no longer on one of the login nodes.

This is a great place to run your code.

Want to give it a try? Download the examples and run the awesome_simulation.py example.

$ git clone https://github.com/ResearchComputing/support.git
$ cd support
$ module load python/anaconda-1.6.1 
$ python awesome_simulation.py -t 5

The awesome_simulation.py is just a place holder for a command you might actually want to run.

Batch Jobs

Interactive jobs are great for testing your code to make sure it works or ideal for debugging your code when you are having issues. When you are ready to run simulations, you will likely want to submit you jobs to the scheduler, which will then run it at a later time. The file that describes what you would like to do is called a PBS script.

It's very simple to submit a job. If you haven't already done so, please download the getting started examples:

$ git clone https://github.com/ResearchComputing/support.git
$ cd support

Then submit an example job to the scheduler:

$ qsub example_01.pbs

This will return immediately with a job number {job_number}.moab.rc.colorado.edu. You can use the {job_number} to check the status of you job:

$ showq -u {username}

will give you a list of your jobs, including the {job_number}.