EINVAL error for setns(target_ns_pid, "user")

[jaharkes]

This is when called from sinfonia-tier3 after the child process has been started with unshare and we are trying to attach the newly created wireguard tun device to the namespace created by unshare.

Have seen this on two systems so far and it seems to be related to how the python virtualenv is set up but the exact reason for the EINVAL error is not clear. So far I've been able to exclude kernel version and python interpreter version differences as culprits.

In one case I had a working and a non-working Ubuntu 20.04 and the only difference seemed to be that the working one used the latest version of pipx (1.2.0) installed from pypi (pip install --user pipx), while the broken installation had both an apt-installed version of pipx (0.12.3.1-2ubuntu1) as well as the pypi version which was causing some other very odd but interesting breakage, like pipx list hanging unless it was run under strace.