Linux Tuning

Summary

There are 3 directories responsible for system tuning.

• /proc/sys ⇐ contians the current system parameters
• /etc/sysctl.d/ ⇐ *.conf if you write the system parameter to a conf file inside this it will be persistent
• /etc/tuned/
  • /etc/tuned/main.conf ⇐ has settings about tuned
  • /etc/tuned/profiles/<profile>/main.conf ⇐ you can create tuned profiles like this

• we use tuned to do system tuning in RHEL
• Kernel tunables are provided through the /proc/sys directory in the /proc pseudo file system
• if you want to see all the system tuning parameters,

sysctl -a

• this will show all the parameters,

• to see how many parameters are there

• if you want to see the value of a parameter,

• Different files in the /proc/sys directory contain the current setting as its value

• Change the current value by echoing a new value into the file:

echo 40 > /proc/sys/vm/swappiness

• but if you write to /proc/sys it is not persistent.

• To make settings persistent, write them to a file in /etc/sysctl.d:

• now this will persist even after a reboot.

• if you want to make it available immedietly then you have to use sysctl -p

sysctl -p /etc/sysctl.d/swappiness.conf

or you can use

sysctl --system

• since there are a lot of tunable parameters, it is hard to manage all of them just by writing to files.

• To make system tuning easier, tuned is provided

• tuned is a systemd service that works with different profiles tuned-adm list shows current profiles

• tuned-adm profile virtual-guest sets another profile as default.

• to see the active profile you can use

tuned-adm active

• Each profile contains a file with the name tuned.conf, that has a wide range of performance related settings
• After creating the directory with the corresponding tuned.conf, it will automatically be picked up
• if you want to see recommend tuned profile

tuned-adm recommend

• The reapply_sysctl = 1 parameter in /etc/tuned/tuned-main.conf ensures that, in case of conflict, the sysctl parameter wins

• tuned --help will provide an overview of all the commands that you can use.

• if you want to create your own tuned profile you can create it like this

• you only need to create the profile. it will automatically will be picked up by tuned

• remember sysctl will win over tuned. if you want to change that behavior you have to set reapply_sysctl = 0 in /etc/tuned/main.conf

How to see all the tunables in a systemd units?

systemctl show httpd.service