Today I've released a new version of uid_wrapper (1.1.0) with full threading support. Robin Hack a colleague of mine spent a lot of time improving the code and writing tests for it. It now survives funny things like forking in a thread. We also added two missing functions and fixed several bugs. uid_wrapper is a tool to help you writing tests for your application. If you don't know uid_wrapper and wonder what you can do with it, here is an example: $ id uid=1000(asn) gid=100(users) groups=100(users),478(docker) $ LD_PRELOAD=libuid_wrapper.so UID_WRAPPER=1 UID_WRAPPER_ROOT=1 id uid=0(root) gid=0(root) groups=0(root) More details about uid_wrapper can be found on the cwrap project website, here.