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Kernel tunables (sysctl)
The Linux kernel offers a plethora of knobs under `/proc/sys` to control the availability of different features and tune performance parameters.
Values under `/proc/sys` can be changed directly at runtime, but such changes will not be persisted across reboots. Persistent settings should be written under `/etc/sysctl.d/` during provisioning, in order to be applied on each boot.
Example: configuring kernel tunable to disable SysRq keys
Further details can be found in the systemd man pages https://www.freedesktop.org/software/systemd/man/sysctl.d.html[sysctl.d(5)] and https://www.freedesktop.org/software/systemd/man/systemd-sysctl.service.html[systemd-sysctl.service(8)].
As an example, the xref:producing-ign.adoc[Butane] snippet below shows how to disable _SysRq_ keys:
variant: fcos
version: 1.4.0
- path: /etc/sysctl.d/90-sysrq.conf
inline: |
kernel.sysrq = 0