Prerequisites: Analysis Code

Introduction

CRAB enables the user to execute their specific analysis code on CMS data or MC samples. Because CMS follows a data location driven computing model, CRAB has to transport the user's analysis job to the sample located at a CMS GRID site and execute it.

User code

A user analysis in CMS terms is based on a chosen CMSSW release. It uses all available functionalities from the chosen base release without the need of compilation. The user can add user specific functionality and also change components of the base release. The user's code takes precedence of the base release itself.

CRAB takes care of the code in the user's CMSSW project directory and uses the pre-installed CMSSW release at the GRID site.

Before submitting a job with CRAB, the user has to

  1. Create a user project area of the chosen CMSSW release (see https://twiki.cern.ch/twiki/bin/view/CMS/WorkBookSetComputerNode for details)
  2. Setup the chosen release by executing
    eval `scramv1 runtime -sh`
    
    using the sh shell family or
    eval `scramv1 runtime -csh`
    
    using the csh shell family
  3. Test the execution of an example job. This is very important. CRAB projects are medium to large scale analysis projects which use a significant amount of resources. Every problem with the analysis job itself caught before submission to the GRID saves resources and does not count for the user's quota.

Example CMSSW analysis job

A short example CMSSW analysis job which simply writes out all information from the input to an output file is presented in the following. The parameter-set contains:

process Test = {

  # initialize  MessageLogger
  include "FWCore/MessageLogger/data/MessageLogger.cfi"

  source = PoolSource
  {
    untracked vstring fileNames = {
      "file:test.root"
    }
    untracked int32 maxEvents = 10
  }

  module out = PoolOutputModule 
  {
    untracked string fileName = 'output.root'
  }

  endpath e = 
  {
    out
  }

}

For testing, any CMSSW root file named test.root can be used.

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Topic revision: r2 - 2007-03-20 - OliverGutsche
 
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