Hi Nils, Thank you for the report. I've tested your example with the jython/2.5.3-9 package currently in unstable and I couldn't reproduce the error on invoking os.chmod(). os.mkdir() still triggers an error when the directory already exists, but it seems the upstream jython runtime has the same behavior.
This issue was probably fixed in the version 2.5.3-4 when the package was adapted to use jnr-posix 3.0.10. Emmanuel bourg
