# Logging environment variables¶

PyPy, and all other RPython programs, support some special environment variables used to tweak various advanced parameters.

## Garbage collector¶

Right now the default GC is (an incremental version of) MiniMark. It has a number of environment variables that can be tweaked. Their default value should be ok for most usages.

## PYPYLOG¶

The PYPYLOG environment variable enables debugging output. For example:

PYPYLOG=jit:log


means enabling all debugging output from the JIT, and writing to a file called log. More precisely, the condition jit means enabling output of all sections whose name start with jit; other interesting names to use here are gc to get output from the GC, or jit-backend to get only output from the JIT’s machine code backend. It is possible to use several prefixes, like in the following example:

PYPYLOG=jit-log-opt,jit-backend:log


which outputs sections containing to the optimized loops plus anything produced from the JIT backend. The above example is what you need for jitviewer.

The filename can be given as - to dump the log to stderr.

As a special case, the value PYPYLOG=+filename means that only the section markers are written (for any section). This is mostly only useful for rpython/tool/logparser.py.

## PYPYSTM¶

Only available in pypy-stm. Names a log file into which the PyPy-STM will output contention information. Can be read with pypy/stm/print_stm_log.py.