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.

As an example, the Butane snippet below shows how to disable SysRq keys:

Example: configuring kernel tunable to disable SysRq keys
variant: fcos
version: 1.5.0
    - path: /etc/sysctl.d/90-sysrq.conf
        inline: |
          kernel.sysrq = 0

Further details can be found in the systemd man pages sysctl.d(5) and systemd-sysctl.service(8).