3.1. basf2: The Main Belle2 Software Executable

The main command line tool for the Belle2 Software is basf2:


Generic Options (to be used instead of steering file)

-h, --help

print all available options

-v, --version

print the version of the Belle2 Software


print information about basf2 and the environment

-m ARG, --modules ARG

Without argument this will print a list of all available Modules. With an extra argument the list can be limited to one package or one specific module.


-l LOGLEVEL, --log_level LOGLEVEL

Set global log level (one of DEBUG, INFO, RESULT, WARNING, or ERROR). Takes precedence over set_log_level() in steering file.

--random-seed SEED

Set the default initial seed for the random number generator. This does not take precedence over calls to set_random_seed() in the steering file, but just changes the default. If no seed is set via either of these mechanisms, the initial seed will be taken from the system’s entropy pool.


Set the default debug level and also enable DEBUG as the default log level. This does not override any settings in the steering file but just changes the defaults. If you want to force debug level please use -l DEBUG

-n N, --events N

Override number of events to be processed, either when reading files or when generating events.


Override run for EventInfoSetter, must be used with -n and –experiment

--experiment EXPNUMBER

Override experiment for EventInfoSetter, must be used with -n and –run

--skip-events SKIPNEVENTS

Override skipNEvents for EventInfoSetter and RootInput. Skips this many events before starting.


Override name of input file for (Seq)RootInput. Can be specified multiple times to use more than one file. For RootInput, wildcards (as in *.root or [1-3].root) can be used, but need to be escaped with \ or by quoting the argument to avoid expansion by the shell.

-S ARG, --sequence ARG

Override the number sequence (e.g. 23:42,101) defining the entries (starting from 0) which are processed by RootInput.Must be specified exactly once for each file to be opened.This means one sequence per input file AFTER wildcard expansion. This are not event numbers but the entry numbers in the input files and the first entry always has number 0.


Override name of output file for (Seq)RootOutput. In case multiple modules are present in the path, only the first will be affected.

-p NWORKER, --processes NWORKER

Override number of worker processes (>=1 enables, 0 disables parallel processing)

Advanced Options

--module-io MODULENAME

Create diagram of inputs and outputs for a single module, saved as ModuleName.dot. To create a PostScript file, use e.g. ‘dot ModuleName.dot -Tps -o out.ps’.


Generate data flow diagram (dataflow.dot) for the executed steering file.


Disable collection of statistics during event processing. Useful for very high-rate applications, but produces empty table with ‘print(statistics)’.


Read steering file, but do not start any event processing when process(path) is called. Prints information on input/output files that would be used during normal execution.

--dump-path FILENAME

Read steering file, but do not actually start any event processing. The module path the steering file would execute is instead pickled (serialized) into the given file.

--execute-path FILENAME

Do not read any provided steering file, instead execute the pickled (serialized) path from the given file.

--profile MODULENAME

Name of a module to profile using callgrind. If more than one module of that name is registered only the first one will be profiled.


The most simple invocation is to just run basf2 with the name of a python steering file to execute:

$ basf2 steeringfile.py

Additional arguments can be given to the steering file which will be available in sys.argv:

$ basf2 steeringfile.py argument1 argument2

To make sure that the arguments are actually passed to the steering file and not consumed by basf2 one should use to dashes -- to separate the arguments which should be passed to the steering file. This allows the steering file to handle options like -o which would otherwise be handled by basf2 and not available in the steering file:

$ basf2 steeringfile.py -- argument1 -o argument3

To specify the input/output files which should be used by basf2 instead of the one configured in the steering file itself one can supply the -i and -o options:

$ basf2 -i input1.root -i input2.root -o output.root steeringfile.py