Submitting Jobs to Lonestar

Overview

The main point of using Lonestar is that it is a massive computer cluster. If we run a command when logged into lonestar, we are running it on one of the two low memory, low power  "head" or "login" nodes on TACC. WHen we do serious computations that are going to take more than a few minutes or use a lot of RAM, we need to submit them to one of the other 1,888 computer nodes and 22,656 cores on Lonestar.

In this section we are going to learn how to submit a job to the Lonestar cluster.

Diagram of how a job gets run on Lonestar

Explanation

Start at the bottom - that's what you want: one of Lonestar's 1,888 compute nodes running your specific program (bowtie mapping in this case).

To get there, you must go through a "Queue Manager" program running on a different computer - the login (or "head") node. This program keeps track of what's running on those 1,888 nodes and what's in line to run next. It's very good at doing this.

You tell the Queue Manager what you want done via "job.sge" - your job submission script. That specifies how many nodes you need, what allocation to use, the maximum run time of the job, etc. The Queue Manager doesn't really care what you're running, just how you want it run. It needs to pass info on what you're running off to the compute node - you do that with the line setenv CONTROL_FILE commands.

The Queue Manager sends off the commands in the file commands to the compute nodes; so commands is really the first thing to start with.

The launcher_creator.py script just helps you by creating jobs.sge easily - saves you some time editing a file (and potentially messing it up).

Launcher

In the examples we tend to say that a job can be "interactive" or should be "submitted to the TACC queue". The first means that you can type it and run it directly. It should be short enough that it does not tie up the TACC head node. The second means that you should go through the launcher submission process described here.

If you do try to run a long job in interactive mode. It will be killed after 10-15 minutes and you may see a message like this:

Message from root@login1.ls4.tacc.utexas.edu on pts/127 at 09:16 ...
Please do not run scripts or programs that require more than a few minutes of
CPU time on the login nodes.  Your current running process below has been
killed and must be submitted to the queues, for usage policy see
http://www.tacc.utexas.edu/user-services/usage-policies/
If you have any questions regarding this, please submit a consulting ticket.

Commands file

A launcher file tells Lonestar which executables to run with your desired options and for how long. It requests a certain amount of resources (cores and time) so that Lonestar's scheduling program figure out where to fit your job in.

All we need to do is create a text file. Each line in this text file, which we will call simply commands, is a command exactly as you would type it into the terminal yourself to have it run.

nano commands
    date > date.out
    ls > ls.out

• The minimum number of processors that you can request on Lonestar is 12, so you might as well add up to 10 more lines to this file that are different shell commands that will give some sort of output. Each will be run on a different core in parallel.

Launcher script

Two ways to skin this cat

1.TACC has supplied a sample launcher script which we can modify to queue and execute our job. Here's how:

 module load launcher
 cp $TACC_LAUNCHER_DIR/launcher.sge ./
 nano launcher.sge

Typically, we would change:

The -N line specifies the name of the job. 

The -o line specifies the names of the output files that Lonestar makes.We would change that to the name of this job.

The -l line specifies the length of time given to the job. The more time we give our job, the longer in the queue our job will wait to be run. When the time is up, Lonestar will terminate our job whether or not it's finished. So it's best to give our job slightly more time than it'll take.

We can also, optionally, add a few lines to have Lonestar send an email to your email address when the job starts and finishes.

To do that, under -V, we would add 2 new lines like so:

 #$ -M my_email@something.com
 #$ -m be

Also, if we are part of multiple allocations, we'll need to specify which allocation to use (Case sensitive).

 #$ -A DNAdenovo  #(or CCBB)

Lastly, we need to specify the job file.

 setenv CONTROL_FILE commands

2. We can use launcher_creator.py to edit the launcher file without even opening it.

We have created a Python script called launcher_creator.py that makes creating a launcher.sge script a breeze. You will probably want to use this for the rest of the course.

Now run the script with the -h option to show the help message:

 module load python
 launcher_creator.py -h

We should mention that launcher_creator.py does some under-the-hood magic for you and automatically calculates how many cores to request on lonestar, assuming you want one core per process. You don't know it, but you should be grateful that this saves you from ever having to think about a confusing calculation.

Lonestar Queue

Next step would be to submit the job to the queue by using the launcher file.

 qsub launcher.sge

Lonestar will make sure that everything specified in the launcher file  is correct and if it is, the job will be queued.

To check the status of the job, the command is:

 qstat

This will tell you its job priority and what state it is in.

A state of "qw"  means "queued."

A state of "r" means "running."

In case we notice something wrong with the job, we can delete it like so:

 qdel job-ID

To obtain the job-ID, look at the  "qstat" output.

For those who are nosy and want to see all of the jobs queued and running on Lonestar, this commands is handy:

 showq

To see just your jobs in this format:

 showq -u

You can create a job that is dependent on another job finishing only start after the first job has completed using this command:

 qsub -hold_jid job-ID launcher.sge

Further reading

• Complete explanation of the options in launcher.sge

TACC Output Files

While your job is running, TACC creates 3 different files with names based on the -o field in the launcher. These files are named like so:

 (job_name).e(job-ID)
 (job_name).pe(job-ID)
 (job_name).o(job-ID)

These files have the output of your job that would have been sent to standard output or standard error and messages from TACC about your job. These files will be useful if your job fails.

Now let's go try all new skills out with a simple exercise...