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Use Proc Sys And Sysctl To Modify And Set Kernel Runtime Parameters
General Information
Modifying runtime or persistent kernel parameters.
Runtime Kernel Settings
Everything in this section are runtime ONLY changes; the values will go back to their original setting upon reboot.
View all tunable kernel parameters
sysctl -a
View the configuration of a specific setting
sysctl vm.swappiness
Write a runtime only configuration change and verify
sysctl -w vm.swappiness=10 sysctl vm.swappiness
- -w → write
Alternative: Echo the value into the correct location in /proc
echo "15" > /proc/sys/vm/swappiness
Persistent Kernel Settings
To make changes that are persistent across reboots…
- Default system values: /usr/lib/sysctl.d/
- Persistent configuration over rides: /etc/sysctl.conf
Create entries in /etc/sysctl.conf
vim /etc/sysctl.conf net.ipv4.ip_forward = 1
Load settings from a file
sysctl -p <filename>
- If no file name is specified, defaults to: /etc/sysctl.conf
Tuned
Tuned is a “dynamic adaptive system tuning daemon”.
Starting in EL 7.2, some parameters (such as vm.swappiness) are set AFTER systemd-sysctl.service by the tuned service.
View the active tuned profile
tuned-adm active
- Location of built in system tuned profiles: /usr/lib/tuned/
- Location of user defined profiles: /etc/tuned
- Example: Create a virtual-guest override file
mkdir /etc/tuned/virtual-guest cp /usr/lib/tuned/virtual-guest/tuned.conf /etc/tuned/virtual-guest/
- Edit the over ride file (/etc/tuned/virtual-guest/tuned.conf), make any changes.
- Restart the tuned service
systemctl restart tuned