(r1) AtlasGrid < Main

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Introductions to GRID can be found in several places (eg. see link 1 or bibliography 1), depending which level the user wants to get into. Here, I'll give rough instructions but I want to focus on tips and give scripts that will make a physicist run his/her jobs and get results fast.

A very good introduction to GRID is given by Steve Lloyd (see link 2) but also at the Atlas Wiki (see link 3). In terms of "bureaucracy" you will need (a) to get a GRID certificate and (b) to join a Virtual Organisation The certicate will be valid only for the machine that you used to issue it. This is very important, since if you need to have access to web-pages (like for example the Grid User Support), you will need to do so using the machine you got the certificate from. Otherwise, you should log-in to that machine and from there do whatever you wish... These steps now take few days (instead of few months, as it used to be)

After that, you will need to get an account on a User Interface and install your certificate. The final aim of doing these steps is to create your proxy certificate, which will allow you to have access to the grid for a desired period of time.

The guides on how to do the above steps are on our group's web-page (see link 4)

By now, you will be able to use the grid. Each time you log in, you should do:

source /usr/local/lcg/etc/profile.d/grid_env.sh

For convinience, you could add this command into your shell script (.bashrc usually)

You have also to get or check if you have a valid grid proxy and if so, for how long. To get a proxy type:

grid-proxy-init -valid 24:30

That will give you a proxy for 1 day (24 hours) and 30 minutes. Caution!! You should make sure that your proxy is valid for the whole period of the run of your jobs. If for example you have the above proxy and you run full simulation of 100 events, then your job will be killed at the expire of your proxy.

Tip: You can use the grid-proxy-(TAB) to get all the commands and --help at the end of the command to see the syntax.

Tip: 3 days proxy is enough for full simulation of 100 events (multi-particle final state samples).

Running a Grid Job

It is essential to understanbd that between you and the site that your job will eventually run, there is the Resource Broker (RB), which controls and distributes the jobs. For us, the RB is RAL. For example, you sumbit your jobs there, and you retrieve your job from there. The concept is that the user doesn't have direct contact with the final site.

To make the first step, run the HelloWorld, described at Steve's notes (link 2). There are three main componets of your job: (a) the .jdl file, which gives the instructions to the RB of what your jobs will need. (b) you .sh file , which is the executable script (the same that we submit at the PBS) and (c) your .py file, which is the normal python jobOptions file that we all run within ATHENA.

Links