Frequently Asked Question

What do pgrep and pkill do that ps | grep | kill doesn't?

pgrep and pkill are purpose-built tools from the procps-ng suite that walk /proc directly, looking for processes whose name, command line, user, terminal, or other attribute matches a pattern. pgrep nginx prints the PIDs of every nginx process; pgrep -a nginx adds the command line; pgrep -u alice finds every process owned by alice; pgrep -f "python myscript" matches the full command line, not just the program name.

pkill is identical to pgrep but sends a signal instead of printing, pkill nginx is the same as kill $(pgrep nginx), plus correct quoting, proper exit codes, and the crucial property that it won't accidentally match the grep process you would otherwise have piped through. Both accept the usual signal flags (pkill -9 firefox, pkill -HUP nginx). Compared with ps -ef | grep … | awk '{print $2}' | xargs kill, they are shorter, safer, and scriptable.