After Upgrading from 18.04 to 20.04 I've notices several warnings during shutdown or reboot like:
Failed to unmount /oldroot: Device or Resource busy Failed to unmount /oldroot/dev/pts: Device or Resource busy Failed to unmount /oldroot/dev: Device or Resource busy Failed to unmount /oldroot/sys: Device or Resource busy
Sometimes it's visible on the screen, sometimes it's covered by the splash.
I cannot find anything related using journalctl or logs, the only thing I've found is:
abr 23 22:24:36 vanburen07-G5-5590 sudo: vanburen07 : TTY=pts/0 ; PWD=/home/vanburen07 ; USER=root ; COMMAND=/bin/umount /oldroot/dev/pts
There's nothing specific in fstab:
<file system> <mount point> <type> <options> <dump> <pass> # / was on /dev/nvme0n1p3 during installation UUID=063c6892-66d6-4598-9dcf-82136ad4ea81 / ext4 errors=remount-ro 0 1 # /boot/efi was on /dev/nvme0n1p1 during installation UUID=C000-EAB9 /boot/efi vfat umask=0077 0 1 /swapfile none swap sw 0 0
The only thing I was able to find were on Arch/Manajaro forums and the suggested workaround is to modify a file that doesn't esxist in Ubuntu: /etc/mkinitcpio.conf
I don't think this is a huge issue as it doesn't cause visible crush or even error in syslogs but yet it'd be nice to know the reason.