Pah! Shut the system down like a real BOFH! Use the Magic SysRq Key interface to instantly crash the system:

  echo 1 > /proc/sys/kernel/sysrq
  echo o > /proc/sysrq-trigger
https://docs.redhat.com/en/documentation/red_hat_enterprise_...

Wouldn’t this potentially leave e.g. disk encryption keys in memory?

You'd probably want to do the filesystem unmount dance first:

  echo 1 > /proc/sys/kernel/sysrq
  echo u > /proc/sysrq-trigger
  dmesg --follow \
  | grep -qm1 'Emergency Remount complete'
  echo o > /proc/sysrq-trigger
...least putting a bit too much trust in ext4/btrfs/zfs journalling.