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Intro to 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 Docker containers you should already have a working CMSSW area.

Info for Mac users!

If you have a Mac and if you ran into challenges in the Docker lesson running the CMSSW_7_6_7 container, you will most likely not be able to execute the code in this lesson.

Don’t worry! :)

You can still read through this lesson to get an idea of how the data winds up being processed. In addition,

  • For the workshop, much of the data will already have been processed and you can then analyze it with docker containers that work better with Mac processors.
  • Or you will be working in a cloud environment, where the docker container will run OK.

If you have closed the container, re-start it with:

docker start -i <theNameOfyourContainer>

Make sure you are in the CMSSW_7_6_7/src area of the container. This is the default directory when you start the container, but if you have changed to another directory, come back to it with:

cd /code/CMSSW_7_6_7/src

Note that we are not really “installing” CMSSW but setting up an environment for it. CMSSW was already installed in the container. Every time you start the container a script runs by default to set up a few environmental variables that are needed.

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

echo $CMSSW_RELEASE_BASE

The variable points to a local CMSSW install in the Docker container:

/cvmfs/cms.cern.ch/slc6_amd64_gcc493/cms/cmssw/CMSSW_7_6_7

Try a different variable

Can you check where the variable CMSSW_BASE points to?

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 expand on this later. For now, let’s try a simple example.

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 Docker container: run with the Demo/DemoAnalyzer/demoanalyzer_cfg.py python configuration file.
To run in a more efficient way, although it is not strictly necessary, we use the bash redirector >, the redirection of stderr to stdout (2>&1), and the trailing run-in-the-background control operator &. This allows us to send the output to a dummy.log file and run the proces in the background so we can still interact with the terminal.

You can check the development of your job with

When finished, if you dumped the content of dummy.log, and do

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_7_6_7 ----
>> 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
>> Subsystem BigProducts built
>> Local Products Rules ..... started
>> Local Products Rules ..... done
gmake[1]: Entering directory `/code/CMSSW_7_6_7'
>> Creating project symlinks
  src/Demo/DemoAnalyzer/python -> python/Demo/DemoAnalyzer
>> Done python_symlink
>> Compiling python modules cfipython/slc6_amd64_gcc493
>> 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 `/code/CMSSW_7_6_7'

Note that scram only goes into the Demo/DemoAnalyzer package that we created locally to validate our setup in a previous lesson. The rest of the packages, that live on the installation area (remember the area where CMSSW_RELEASE_BASE points to), 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 be 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.

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 used already to create the DemoAnalyzer package. This script creates skeletons for EDAnalyzers that can be later 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 (maybe twice):

mked + Tab + 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. 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/python/ConfFile_cfg.py config file of your analyzer package. Try to figure it out from the documentation above before looking at the solution.

Solution

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

So, the ROOT file has 49871 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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