This application example will cover the use of the ROOT data analysis framework on OSG Connect. In this example, we'll use Parrot in order to access CVMFS on any worker node, regardless of whether or not it is natively mounted.
ROOT is a piece of software commonly used in high energy physics. We'll use a sample piece of code (shamelessly stolen from Ilija Vukotic) that prints all of the TTrees and their branches for a given ROOT file.
For this example, we're going to use ROOT in a manner similar to a typical ATLAS job. The first thing to do is set up our working directory for the tutorial, or simply run 'tutorial root'.
[username@login01 ~]$ mkdir -p root/log; cd root
We'll need to run a few scripts to get the ROOT environment set up properly. This will add ROOT to our PATH and point LD_LIBRARY_PATH at the correct libraries.
[username@login01 root]$ source environment.sh Setting up gcc Setting up ROOT Setting up xRootD [username@login01 root]$ root -l *** DISPLAY not set, setting it to 10.150.25.138:0.0 root 
There are some complaints about DISPLAY, but that's alright because we don't plan to do anything requiring X11 graphics. You can quit out of root with '.q'
root  .q [username@login01 root]$
We're going to need some ROOT code, as well as a Makefile to compile it. Here is the ROOT code:
[username@login01 root]$ make g++ -O2 -Wall -fPIC -pthread -m64 -I/cvmfs/atlas.cern.ch/repo/ATLASLocalRootBase/x86_64/root/5.34.18-x86_64-slc6-gcc4.7/include -c -o inspector.o inspector.C
g++ -O2 -m64 inspector.o -L/cvmfs/atlas.cern.ch/repo/ATLASLocalRootBase/x86_64/root/5.34.18-x86_64-slc6-gcc4.7/lib -lCore -lCint -lRIO -lNet -lHist -lGraf -lGraf3d -lGpad -lTree -lRint -lPostscript -lMatrix -lPhysics -lMathCore -lThread -pthread -lm -ldl -rdynamic -lTreePlayer -o inspector
Let's try it out. We're going to be remotely reading data from the a XRootD filesystem. Replace ROOT-FILE below with the location of a ROOT file with event data
[username@login01 root]$ ./inspector ROOT-FILE | head -n10 1 susy:16076:199459108:2505 EF_e20_medium 5071 EF_e22_medium 5080 EF_e22vh_medium1 5391 EF_e45_medium1 6958 EF_mu18 6806 EF_mu18_MG 6881 EF_mu18_MG_medium 7066 EF_mu18_medium 6987
Suchandra has spoken a bit about Parrot for data access. I've written a bit of shell code to do that for you, just like in the previous example ROOT-FILE will need to be replaced with the location of a ROOT file.
Building an HTCondor Job
Creating a job submit file for this code is pretty straightforward. The wrapper script does the bulk of the heavy lifting, we just have to make sure we are transferring the appropriate files. The requirements line is optional here, but I've included it because I'd like to see my job run on OSG.Let's submit the code
[username@login01 root]$ condor_submit root.submit Submitting job(s). 1 job(s) submitted to cluster 85995.
We can see that it's running:
[username@login01 root]$ condor_q username -- Submitter: login01.osgconnect.net : <188.8.131.52:42546> : login01.osgconnect.net
ID OWNER SUBMITTED RUN_TIME ST PRI SIZE CMD 85995.0 username 5/20 13:16 0+00:00:05 R 0 0.0 wrapper.sh
This code puts all of its output on stdout, so let's check the output:
[username@login01 root]$ tail -n10 log/out.85995.0 vx_m 465260 vx_n 16759 vx_nTracks 223060 vx_px 480170 vx_py 480150 vx_pz 481488 vx_sumPt 465725 vx_x 481620 vx_y 444255 vx_z 499665 c-110-34.aglt2.org