Capture a Background Job's PID with $!

Backgrounding a job is only half the story — to manage it later you need its PID. The program /usr/local/bin/collector.sh runs until killed; it isn't running yet.

Start it in the background AND write its process id to the file /root/collector.pid (just the PID number), so an ops script can stop it later with kill "$(cat /root/collector.pid)".

Grading checks that the collector is running and that /root/collector.pid holds THAT process's real PID — a guessed number won't pass, and neither will the PID of some other process.