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.