====== Use Proc Sys And Sysctl To Modify And Set Kernel Runtime Parameters ======
**General Information**
Modifying runtime or persistent kernel parameters.
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====== Lab Setup ======
The following virtual machines will be used:
* server1.example.com (192.168.1.150) -> Configure the kernel parameters here
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====== Help ======
Finding help in this section.
* Sysctl man pageman sysctl
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====== Runtime Kernel Settings ======
Everything in this section are runtime ONLY changes; the values will go back to their original setting upon reboot.
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View all tunable kernel parameters
sysctl -a
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View the configuration of a specific setting
sysctl vm.swappiness
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Write a runtime only configuration change and verify
sysctl -w vm.swappiness=10
sysctl vm.swappiness
# Or
sysctl -a | grep swappiness
* -w -> write
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Alternative: Echo the value into the correct location in /proc
echo "15" > /proc/sys/vm/swappiness
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====== Persistent Kernel Settings ======
To make changes that are persistent across reboots...
* Default system values: /usr/lib/sysctl.d/
* Persistent configuration over rides: /etc/sysctl.d/filename.conf
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Create entries in /etc/sysctl.d/mychanges.conf
vim /etc/sysctl.conf
net.ipv4.ip_forward = 1
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Load settings from a file
sysctl -p /etc/sysctl.d/mychanges.conf
* If no file name is specified, defaults to: /etc/sysctl.conf
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Load all settings
sysctl --system
===== Tuned =====
Tuned is a "dynamic adaptive system tuning daemon".
* **Notes**
* Starting in EL 7.2, some parameters (such as vm.swappiness) are set AFTER systemd-sysctl.service by the tuned service.
* In EL 7.4, it appears that tuned defaults to honor sysctl (/etc/tuned/tuned-main.conf)....SNIP....
# Whether to reapply sysctl from the e.g /etc/sysctl.conf, /etc/sysctl.d, ...
# If enabled these sysctls will be re-appliead after Tuned sysctls are
# applied, i.e. Tuned sysctls will not override system sysctls.
reapply_sysctl = 1
....SNIP....
* Either way; be aware of tuned and its potential to conflict with sysctl.
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View the active tuned profile
tuned-adm active
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* Location of built in system tuned profiles: /usr/lib/tuned/
* Location of user defined profiles: /etc/tuned
* **Example**: Create a virtual-guest override filemkdir /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 servicesystemctl restart tuned
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