If you are using the Python destination (not the program() destination executing the python3 binary), then syslog-ng does not use the Python binary at all.

The python() destination starts a separate thread inside syslog-ng instead, and uses the libpython library to interpret Python code.

In case you have syslog-ng compiled with Python 3 support, you can specify which libpython to use with the LD_LIBRARY_PATH environment variable or with standard ldconfig configurations.

For example: /apps/lib/libpython3.so --> LD_LIBRARY_PATH=/apps/lib

A syslog-ng instance compiled with Python 2 support currently can't be configured to use Python 3, you have to recompile it from source in this case (./configure --enable-python --with-python=3, for example).

The PKG_CONFIG_PATH envvar can be used to help the configure script find the appropriate path to libpython.

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László Várady