zeroroot.sh

#!/bin/bash

# zero all the free blocks on a (mounted) root fs to TRIM it
# and/or make it more compressible for backups
# during this process the machine is basically dead (only ssh works)
# reboots at the end

systemctl isolate rescue-ssh
sleep 3
systemctl stop systemd-journald.socket
systemctl stop systemd-journald-audit.socket
systemctl stop systemd-journald-dev-log.socket
systemctl stop systemd-journald
systemctl stop systemd-udevd-control.socket
systemctl stop systemd-udevd-kernel.socket
systemctl stop systemd-udevd

sleep 10

systemctl stop systemd-journald.socket
systemctl stop systemd-journald-audit.socket
systemctl stop systemd-journald-dev-log.socket
systemctl stop systemd-journald
systemctl stop systemd-udevd-control.socket
systemctl stop systemd-udevd-kernel.socket
systemctl stop systemd-udevd

echo s > /proc/sysrq-trigger
sleep 1
echo u > /proc/sysrq-trigger
sleep 1

zerofree $(findmnt -no SOURCE /)

systemctl reboot