linuxexpert-practice-labs/labs/rhcsa/4-3-processes-and-priorities/README.md

RHCSA 4.3: Processes and scheduling priority

Finding and ending busy processes, starting a process with a nice value, changing the nice value of a running one, and listing the processes using the most memory.

Before you start

The lab starts two sha256sum /dev/zero processes as root, each using a whole CPU. Nothing in this lab survives a reboot: do it all in one boot.

Tasks

1. Find the process using the most CPU with top, and end both of the lab's sha256sum processes.
2. As a normal user, start sha256sum /dev/zero with a nice value of 10, in the background, and leave it running.
3. As root, change that process's nice value to -5.
4. Save the PID, user and memory use of the five processes using the most memory to /root/topmem.txt: a header line and five process lines, largest first.

Hints

• In top, P sorts by CPU and k kills; or pgrep, kill, pkill.
• nice -n 10 sha256sum /dev/zero &; ps -o pid,ni,user,cmd -C sha256sum.
• renice -n -5 -p PID; only root may lower a nice value.
• ps -eo pid,user,%mem --sort=-%mem | head -n 6.