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.

This shows how to disable SysRq keys:

Example: configuring kernel tunable to disable SysRq keys
# /usr/lib/sysctl.d/90-sysrq.conf
kernel.sysrq = 0

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