The s6-linux-init-umountall program
s6-linux-init-umountall unmounts all filesystems.
- s6-linux-init-umountall unmounts all filesystems according to /proc/mounts.
It processes /proc/mounts in the reverse order, starting with the most recently mounted
partition and ending with the root filesystem ("unmounting" the root filesystem means remounting
- It makes an exception for the first instances of devtmpfs, proc
and sysfs filesystem types, but not for later instances. In other words: it
does not attempt to unmount /dev, /proc and /sys, but it
will attempt to unmount duplicates of those pseudo-filesystems.
- s6-linux-init-umountall does not touch /etc/mtab.
- If a filesystem fails to unmount, a warning is printed to stderr, but
s6-linux-init-umountall still attempts to unmount all the other ones.
s6-linux-init-umountall returns the number of errors it encountered
when attempting to unmount the filesystems listed in /proc/mounts.
- s6-linux-init-umountall is automatically called at the very end of the shutdown procedure,
in "stage 4", i.e. after a SIGKILL has been sent to all the processes on the system, and
right before the system reboots (or halts, or is powered off). By that point, there is
no possible process that could prevent real file systems from being unmounted.
- It is likely that some filesystems will still fail to unmount, typically
cgroups or tmpfses. That's okay: those are pseudo-filesystems, and
will not cause data loss or a fsck if the system shuts down while they are still mounted.
- Distributions usually provide a umount command with a -a option
to unmount all filesystems. That command is usually bloated with historical artifacts
and relies on unsafe interfaces, so it was decided not to use it.