Skip to content

Your first run

This page walks you through a minimal end-to-end run: a single command that exercises the whole FLAF pipeline — from CMS NanoAOD all the way to a histogram plot — on just a handful of events. It is the same smoke test that the continuous integration runs on every change, so if it works for you, your setup is healthy.

Before you start

You need a working environment from Installation:

cd HH_bbtautau          # or your analysis repository
source env.sh           # once per shell
voms-proxy-info         # confirm you have a valid proxy

You also need two settings in config/user_custom.yaml:

  • a storage location for outputs (the fs_default field), and
  • phys_model: TestModel — a small, fast subset of processes meant for testing.

See the Configuration guide for a ready-to-copy minimal file.

Run it

law run FLAF.Analysis.tasks.HistPlotTask \
  --version my_first_run \
  --period Run3_2022 \
  --workflow local \
  --branches 0 \
  --test 1000

That one command asks LAW for the final plots. LAW notices that none of the inputs exist yet and automatically runs every upstream stage first — resolving the input file list, producing and merging analysis ntuples, computing observables, filling and merging histograms — before making the plot. You do not run the intermediate tasks yourself.

What each argument means

Argument Meaning
FLAF.Analysis.tasks.HistPlotTask The task you want — here, the plotting task (the end of the chain).
--version my_first_run A label for this run. Outputs are grouped under it, so you can keep runs apart. Use any name.
--period Run3_2022 Which data-taking era to process.
--workflow local Run on this machine (not the batch system). Good for testing.
--branches 0 Only the first work unit. HistPlotTask has one branch per variable, so this plots a single variable.
--test 1000 Process only 1000 events per input file — fast, just to check the machinery.

These and many more options are catalogued in Command arguments.

What to expect

  • LAW prints a dependency tree and then runs the stages bottom-up. Because the early stages produce analysis ntuples from CMS NanoAOD (using CMSSW and reading from the grid), the first run is not instant even with --test 1000 — budget a little time.
  • Output is written under the storage you configured in user_custom.yaml, organised by version and era. A local copy of small artifacts also appears under data/.
  • When the top task finishes, LAW reports success for HistPlotTask.

Check progress without running anything

In another shell (after source env.sh), ask LAW for the status of the dependency tree: 

law run FLAF.Analysis.tasks.HistPlotTask \
  --version my_first_run --period Run3_2022 --print-status 3,1
The numbers are task depth and file-collection depth. This is the quickest way to see which stage is done and where its output lives.

If it fails

  • InputFileTask keeps appearing / DAS errors — usually a wrong era/version or an expired proxy. Re-run voms-proxy-init. See Troubleshooting.
  • law: command not found — you did not source env.sh in this shell.
  • Import errors / empty submodule dirs — you cloned without --recursive; run git submodule update --init --recursive.

More symptoms and fixes are collected in Troubleshooting.

Next steps

You have run the whole pipeline once. Now learn what actually happened: