linuxexpert-practice-labs/labs/lpic-1/103-6-process-priorities

LPIC-1 103.6: Process priorities

Sharing a CPU between niced processes, who may lower a nice value, and how nice passes on to child processes.

Before you start

The lab creates user dana (password Lab-Pass-1) and starts a long sleep process owned by her at nice value 10. Write answers to the files in /root/lab-answers/. The process doesn't survive a reboot, so check before you reboot.

Tasks

1. Start two CPU-heavy loops pinned to the same CPU, one at the default and one niced: taskset -c 0 sh -c 'while :; do :; done' & and taskset -c 0 nice -n 19 sh -c 'while :; do :; done' &. Watch their CPU share in top, then end them with kill %1 %2. Check it yourself: the niced loop gets only a few percent.
2. As dana, try to renice her sleep process from 10 to 5 and read the error. Then do it as root.
3. Run nice with no arguments, then nice bash and run nice again inside the new shell. Write what nice printed inside the new shell to /root/lab-answers/3.

Hints

• top shows NI and %CPU; q quits.
• su - dana (or sudo -iu dana), pgrep -u dana sleep, renice -n 5 -p PID; ps -o pid,ni,comm -u dana.
• nice alone prints the current nice value; nice CMD adds 10.