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CMSSW

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Installation and Execution

Overview

Teaching: 0 min
Exercises: 20 min
Questions

  • How do I install CMSSW?

  • How do I compile and execute CMSSW?

Objectives

  • Review the steps necessary to setup a CMSSW area.

  • Learn how to compile and execute CMSSW jobs.

Setting up your CMSSW area

If you completed the lessons on virtual machines or Docker you should already have a working CMSSW area.

Make sure you change directories to the CMSSW_5_3_32/src area; for instance, in Docker:

cd /home/cmsusr/CMSSW_5_3_32/src

Note that we are not really “installing” CMSSW but setting up an environment for it. CMSSW was already installed. This is why every time you open a new shell you will have to issue the cmsenv command, which is just a script that runs to set some environmental variables for your working area:

cmsenv

Now you can check, for instance, where your CMSSW_RELEASE_BASE variable points to:

echo $CMSSW_RELEASE_BASE

The variable may point to a local CMSSW install if you are using a Docker container:

/opt/cms/slc6_amd64_gcc472/cms/cmssw/CMSSW_5_3_32

or to a place in the shared cvmfs area if working in a virtual machine:

/cvmfs/cms.cern.ch/slc6_amd64_gcc472/cms/cmssw/CMSSW_5_3_32

cmsRun, the CMSSW executable

All the packages that comprise the CMSSW release in use have been already compiled and linked to one single executable, which is called cmsRun. So, unless you want to create your own plugin (addition) for the software, you won’t even have to re-compile. You can actually try to execute this command by itself, but it will give you a configuration error:

cmsRun

cmsRun: No configuration file given.
For usage and an options list, please do 'cmsRun --help'.

So, inevitably, the cmsRun executable needs a configuration file. This configuration file must be written in Python. Do not worry, we will learn all about configuration in a next episode of this lesson.

Run with a configuration

Now try to run, but this time with a configuration file.

Solution

We could simply repeat what we already did while setting up our VM or container: run with the Demo/DemoAnalyzer/demoanalyzer_cfg.py python configuration file. However, this time we could store the output in a dummy.log file and run it in the background. Notice the bash redirector >, the redirection of stderr to stdout (2>&1), and the trailing run-in-the-background control operator &.

You can check the development of your job with

When finished, if you dump the content of dummy.log

you’ll get an output similar to:

Compilation

We use scram, the release management tool used for CMSSW, to compile (build) the code:

scram b

Reading cached build data
>> Local Products Rules ..... started
>> Local Products Rules ..... done
>> Building CMSSW version CMSSW_5_3_32 ----
>> Entering Package Demo/DemoAnalyzer
>> Creating project symlinks
  src/Demo/DemoAnalyzer/python -> python/Demo/DemoAnalyzer
>> Leaving Package Demo/DemoAnalyzer
>> Package Demo/DemoAnalyzer built
>> Subsystem Demo built
>> Local Products Rules ..... started
>> Local Products Rules ..... done
gmake[1]: Entering directory `/home/cmsusr/CMSSW_5_3_32'
>> Creating project symlinks
  src/Demo/DemoAnalyzer/python -> python/Demo/DemoAnalyzer
>> Done python_symlink
>> Compiling python modules cfipython/slc6_amd64_gcc472
>> Compiling python modules python
>> Compiling python modules src/Demo/DemoAnalyzer/python
>> All python modules compiled
>> Pluging of all type refreshed.
>> Done generating edm plugin poisoned information
gmake[1]: Leaving directory `/home/cmsusr/CMSSW_5_3_32'

Note that scram only goes into the Demo/DemoAnalyzer package that we created locally to validate our setup in a previous lesson. All the rest of the packages in the release were already compiled. Since there is nothing new to compile, it finishes very quickly. In a later episode we will modify this DemoAnalyzer and will need to compile again.

Point to be made: if you compile at main src level, all the packages in there will compiled. However, if you go inside a specific package or sub-package, like our Demo/DemoAnalyzer, only the code in that subpackage will be compiled.

Note: if you are using a soft link to an area that is perhaps mounted from the host machine (like in the example from the Docker lesson), you must compile at the main src level, i.e., /home/cmsusr/CMSSW_5_3_32/src, otherwise the compilation will fail. A small price to pay for convenience.

Additional goodies

Your CMSSW environment comes with other executable scripts/tools that can be very useful. An example of those is the mkedanlzr script that we use already to create the DemoAnalyzer package. This script creates skeletons for EDAnalyzers that can later be modified or expanded. Notice that this package, DemoAnalyzer, has a similar structure as any of the CMSSW packages we mentioned before.

One can find out about other scripts like mkedanlzr by typing mked and hitting the Tab key:

mked + Tab

mkedanlzr  mkedfltr   mkedlpr    mkedprod

In this workshop, however, we will not be using those other ones.

There are also additional scripts, like the Event Data Model(EDM) utilities, the hltGetConfiguration trigger dumper, or the cmsDriver, which can be very useful. We will talk a bit about these later in the workshop, but now let’s check an example.

Finding the EventSize of a ROOT EDM file

Now, as a simple exercise, use one of the EDM utilities mentioned above to find out about the number of events in the ROOT file that is in the Demo/DemoAnalyzer/demoanalyzer_cfg.py config file of your analyzer package.

Solution

After checking the documentation above, the following one-liner will work.

So the ROOT file has 12279 events.

Key Points

  • A CMSSW area is not really installed but set up.

  • cmsRun is the CMSSW executable. There are also utilitarian scripts.

  • You can compile CMSSW with scram b

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