pgrep
ProcessesPackage: procps
Finds PIDs by name or pattern, without the grep that matches itself. pgrep -a shows the command too, which saves killing the wrong process at the next step.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
pgrep -a- Prints the full command line beside the PID, instead of the number alone.
pgrep -f- Matches against the whole command line, not just the program name. Necessary for
node /srv/app/server.js, whose process name is onlynode. pgrep -u- Restricts to a given user.