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Intro to the Cluster and Grid Computing

What is Tier3 Site?
The CMS Grid computing system allows the great output of information acquired by the experiments to be stored, accessed, and analyzed around the world. This pdf will give you a brief description of what this type of Tier does.
In general, CMS software (CMSSW) is used, which includes CRAB (version 2 only supported) as the job handler, submitting to Condor or SLURM (condor is preferred).

Getting the Accounts

HPRC
To get a HPRC account, read this section of general new user guide
 
CERN account

In order to access some the sites that provide instructions you will need a personal certificate, provided by CERN, for your browser. The steps you should take differ depending on your current status.

  • If you are renewing your certificate: you should follow the email from CERN to generate a new certificate

Useful Documents and links

Setting Up CMSSW

Luckily ,in HPRC we have ready scripts that will setup the needed environment for you. Although, to use the script, you should be a member of Mitchcomp group. you can request a membership by emailing Mitchcomp help.
To setup your environment do the following:

>$ source /scratch/group/mitchcomp/bin/cms-setup
>$ source /cvmfs/cms.cern.ch/cmsset_default.sh

Now your environment is ready! The next step is to create CMSSW release in your working area (Use a $SCRATCH subdirectory! DO NOT use your home area)

>$ cd $SCRATCH
>$ mkdir CMS
>$ cd CMS
>$ cmsrel CMSSW_10_2_18 #replace 10_2_18 with your desired version

Now your CMSSW release is ready to use! You can setup your runtime environment by:

>$ cd $SCRATCH/CMS/CMSSW_10_2_18/src #replace 10_2_18 with the version you want to use
>$ cmsenv

Everytime, to initiate your runtime environment, you need to setup your environment all over again, but you don’t need to create the CMSSW release again.

>$ source /scratch/group/mitchcomp/bin/cms-setup
>$ source /cvmfs/cms.cern.ch/cmsset_default.sh
>$ cd $SCRATCH/CMS/CMSSW_10_2_18/src #replace 10_2_18 with the version you want to use
>$ cmsenv

Running and Submitting Jobs

First, make sure you read Running and Submitting Jobs part of our Learning the System guide.

If you want to run batch jobs with CVMFS, you need to modify your job script a bit in HPRC Terra. You cannot normally use CVMFS setup script (/scratch/group/mitchcomp/bin/cvmfs-setup) as part of your script. The reason is that it uses “exec” to make the parrot_run executable replace your login. That way, when you exit or log out, it logs out out completely from Terra, and doesn’t dump you back to a parent shell.

What you need to do is to add these lines to load the CVMFS module and set up your environment: 

export PARROT_CVMFS_ALIEN_CACHE=/scratch/group/mitchcomp/CVMFS_cache
cmsSite=/scratch/group/mitchcomp/CMS/LOCAL_TAMU_HPRC
cmsMount=--mount=/cvmfs/cms.cern.ch/SITECONF/local=$cmsSite

Now you can use parrot_run to do your CMS activity using an external script:

parrot_run $SHELL THESCRIPT.sh #(IF ANY)

Or you can warp the parrot_run around your CMS activity using a HERE pipe with “EOF” as ending symbol:

parrot_run $cmsMount $SHELL << EOF
shopt -s expand_aliases
YOUR COMMANDS
EOF

If you had any problem, don’t hesitate to contact Mitchcomp Help

ROOT

To access root under CMSSW runtime environment, first initialize your CMSSW runtime environment, and then simply use the command “root” to start the ROOT executable:

>$ source /scratch/group/mitchcomp/bin/cms-setup
>$ source /cvmfs/cms.cern.ch/cmsset_default.sh
>$ cd $SCRATCH/CMS/CMSSW_10_2_18/src #replace 10_2_18 with the version you want to use
>$ cmsenv
>$ root

File Transfer

To transfer your files to/from HPRC please read this part of the Mitchcomp’s HPRC Experienced User Guide

Mitchcomp Group Directories

The Mitchcomp group directory for CMS users on both Terra and Grace are located

/scratch/group/mitchcomp/CMS

Whenever you create a subdirectory in the Mitchcomp CMS space, please set up the permissions for them so multiple people can write into them:

chmod g+ws