General Information

Modifying runtime or persistent kernel parameters.

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

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

Note: Starting in CentOS 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