This adds a new output mode "pipe" that is identical to the existing
"background" mode except for that its stdout is redirected into a
pipe so that it can be retrieved.
Before this commit, pmb.helpers.run_core.sanity_checks would raise
a runtime error when pmb.helpers.run.root was called with an output
mode that did not support timeouts (like background).
While at it, also remove unnecessary "#!/usr/bin/env python3" in files
that only get imported, and adjust other empty/comment lines in the
beginnings of the files for consistency.
This makes files easier to read, and makes the pmbootstrap codebase more
consistent with the build.postmarketos.org codebase.
When the timeout occurs it is important to ensure clean up of child
processes. Killing only the direct process created by a command can
leave child processes running.
For example a pmbootstrap.py install will run apk add. This run command
creates multiple processes as follows:
(cmd line arguments snipped for readability)
$ ps -e -o pid,ppid,pgid,cmd
PID PPID PGID CMD
31738 23247 31738 python3 ./pmbootstrap.py -t 15 install --no-fde
31746 31738 31738 sudo env -i /bin/sh -c ... ;apk --no-progress add
31747 31746 31738 /bin/sh -c ... ;apk --no-progress add
31748 31747 31738 apk --no-progress add
The root process of the run command is PID 31746. We want to kill
the child processes too. Otherwise only running kill -9 31746 will leave
the processes 31747 and 31748 running.