Should we specify the timeout explicitly here? Otherwise we use the default (of I think 5s) and we are actually not aware what timeout we will have here?

/bin/sh vs /bin/bash below

I would use a non-login shell here to isolate: ["/bin/bash", "-c", cmd],

Nit: you could use deadline = time.monotonic() + timeout here, then

    try:
        while True:
            remaining = deadline - time.monotonic()
            if remaining <= 0:
               # raise timeout errro

This needs to be a continue, no? Otherwise we would quit in the first iteration if we haven't received any events yet

Do we need to check if the process has finished?

if not chunk:
   if proc.poll() is not None:
      break

proc.poll() check is added after poller.poll()

missing empty line at EOF

Revert the addition of pexpect

restore the old lockfile to revert the addition of pexpect

This error also gets raised if the subprocess finishes within the timeout. I think we split it up:

• time ran out -> timeout error
• process finished without expected output -> expected output not found error
  ( you can set a timed_out variable in the if remaining_ms <= 0 block)

text=True switches subprocess stdout to a text stream, but further down you're using os.read() and decode which normally operates on raw bytes.I think in a polling context this might actually be problematic.? If there's no specific reason switch this to text=False

Probably we also want the if proc.poll() is None: condition here. Otherwise it can happen that we try to kill the process that has exited gracefully already

Nit:; Actually raises AssertionError