Overview

idev (short for interactive development) sessions on TACC are a method of accessing one of the compute nodes directly rather than sending a slurm job off using the sbatch command. In this course, it will let us view the text that would normally print to the screen. We will further benefit from TACC setting up a reservation for us that will allow us to skip the queue and immediately launch an interactive session so we spend our class time working rather than waiting.

Learning Objectives

Learn the importance of launching an idev session
Launch an idev instance
Check if you are currently in an idev session.

Tutorial

Importance of using idev sessions

As mentioned in the introduction tutorial, idev sessions are important to get off the head node and not negatively impact all other TACC users. As mentioned in the bowtie2 tutorial failure to do so has actually caused TACC to crash in previous years, and none of us (you included) want to be part of that happening again. As such most tutorials will contain a warning box similar to this and a link back to this page to ensure you are staying on an idev node and not being a bad TACC citizen.

Launching an iDev session with a reservation

As we discussed in our first tutorial the head node is a space shared by all and we don't like stepping on each others toes. An idev (or interactive development) session is a way to move off the head node and onto a single compute node, but work interactively to see if your commands actually work, give you much quicker feedback, and if everything goes as you hope, your data. idev sessions are not used as often as the queue system (which will be discussed on Friday) as in general its not necessary to see every line a program spits out once you are familiar with the type of data you will get. Additionally, we are going to use a priority access reservation set up special for the summer school that you normally would not have access to but should guarantee immediate starting of your idev session.

Your idev command line will contain 3 flags: -m, -r -A. Using the `idev -h` command, can you figure out what these 3 flags mean and what you told the system you wanted to do?

Click here to see if you are correct...

From the OPTIONS: section of the idev help output:

-m minutes sets time in minutes (default: 30)

-r reservation_name requests use of a specific reservation

-A account_name sets account name (default: -A none)

So you will request an idev node using the reservation named GVAday#, where # is the day of the class and asked that it be charged to the account named UT-2015-05-18.

The question becomes 'how long do we need to request the idev node for'? As the reservation only runs between 9am and 12pm each day this week, you need to request the enough minutes to set it to end a few minutes before 12:00 so the session will start. If you set it to end after 12:00 it won't actually launch.

Copy and paste the following command replacing the trailing 3 ? marks with the number of minutes you want your idev session to last:

Starting an idev session

idev -r GVAday2 -A UT-2015-05-18 -m ???

The very first line of output should be.

 -> Reservation      : GVAday2

A few lines down from that you should see

 -> Reservation name : GVAday2  (reservation ACTIVE  )
 -> Queue            : normal         (reservation         )

If for any reason you don't see the lines above let me know on zoom. As mentioned above, trying to complete most of the tutorials on the head node will cause problems for you or everyone.

You may see something like the following

We need a project to charge for interactive use. 
We will be using a dummy job submission to determine your project(s). 
We will store your (selected) project $HOME/.idevrc file. 
Please select the NUMBER of the project you want to charge.\n 
1 OTHER_PROJECTS
2 UT-2015-05-18


Please type the NUMBER(default=1) and hit return:

If you see the text prompting for a number MAKE SURE you select the number associated with the 'UT-2015-05-18' project.

Finally, everyone will then see something like the following:

 -> Job is now running on masternode= c401-011...OK
 -> Sleeping for 7 seconds...OK
 -> Checking to make sure your job has initialized an env for you....OK
 -> Creating interactive terminal session (login) on master node c401-011.

TACC Stampede2 System
Provisioned on 08-May-2017 at 13:27

If the above takes more than 60 seconds without giving you your prompt back, again get my attention and be ready to share your screen so we can figure out what is going on. I know there were some issues in last weeks course that required assistance from people at TACC.

Verifying you are in an iDev session

It is best to check if you are on an idev session before executing a command that you expect to be taxing for TACC to execute.

The simplest way is to use the following command

hostname

If you are not on an idev node you should see something like login2.stampede2.tacc.utexas.edu where a login node prefixes the stampede2.tacc.utexas.edu address. Otherwise you should see something like: c455-011.stampede2.tacc.utexas.edu where a computer number has prefixed the stampede2 address. Additionally, the "showq" command is available on head node, while it is not available within an idev node.

Launching an iDev session without a reservation

The same command used above can be used, omitting the '-r' flag. The output then becomes much more simple as at most you will be prompted for a choice of what allocation to use.