linux.py uses context message API before initialization

Summary

linux.py causes AssertError for message handler when ran without root.

Steps to reproduce

I witnessed this bug with a gitlab runner which was unprivileged.

See this LOC

What is the current bug behavior?

An AssertError is raised causing the job to fail.

What is the expected correct behavior?

The warning...

Relevant logs and/or screenshots

The LOC causing the problem

Possible fixes

Figure out where the message handler is initialized and shift it?

Other relevant information

  • BuildStream version affected: master