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Using signals to manage process state

man 7 signal

The kill command is used to send signals to PIDs
- Alternatively, you can use k from top
Different kill-like commands exist, like pkill and killall

Note: for RHCSA, only nice and renice is needed

If processes are equal from a perspective of Cgroups, the Linux nice and renice commands can be used to manage priority
nice values range from -20 to 19, with -20 being the highest priority, and 19 the lowest
Users can only decrease the priority of their processes
nice -n 19 dd if/dev/zero of=/dev/null
Priority is always relative to other processes

Kernel tunables are provided through the /proc/sys directory in the /proc pseudo file system
Change the current value by echoing a new value into the file
- cat /proc/sys/vm/swappiness
- echo 40 > /proc/sys/vm/swappiness
To make settings persistent, write them to a file in /etc/systctl.d

cat >> swappiness.conf << EOF
vm.swappiness = 40
EOF

tuned-adm list shows current profiles
tuned-adm profile {profile} sets another profile
Each profile contains a file with the name tuned.conf that has a wide range of performance related settings
The reapply_sysctl=1 parameter in /etc/tuned/tuned-main.conf ensured that, in case of conflict, the sysctl parameter wins

ps -u username to show processes owned by a specific user
pkill -u username to remove processes owned by a specific user
loginctl is a part of systemd, which manages users and sessions
loginctl list-users and loginctl list-sessions shows users and sessions
loginctl user-status {UID} shows a tree of processes currently opened by this user
loginctl terminate-session and loginctl terminate-user can be used to stop current sessions or users

Install and enable tuned
Determine the current and recommended tuned profiles
Set the tuned profile to the recommended profile
Create a user mac and open a shell as this user
As mac, run two background processes sleep inf, one of them with the highest possible priority, the other one with the lowest possible priority
Use the most efficient way to terminate all current sessions for user mac

Solution