[Bug 1928200] Re: Prompt error message "Failed to unmount /oldroot" when shutdown or reboot

[Dan Streetman]

ubuntu at lp1928200-f:~$ cat /etc/binfmt.d/TestFormat.conf 
:TestFormat:M::XX::/bin/true:F
ubuntu at lp1928200-f:~$ dpkg -l systemd|grep systemd
ii  systemd        245.4-4ubuntu3.6 amd64        system and service manager

reboot to pick up change...

reboot again to show issue...

[  OK  ] Reached target Reboot.
[   35.164202] sd-umoun[1548]: Failed to unmount /oldroot: Device or resource busy
[   35.174070] shutdown[1]: Failed to finalize  file systems, ignoring
[   35.219215] reboot: Restarting system


ubuntu at lp1928200-f:~$ dpkg -l systemd|grep systemd
ii  systemd        245.4-4ubuntu3.8 amd64        system and service manager

reboot to pick up change...

reboot again to check issue...

[  OK  ] Reached target Reboot.
[   22.494535] reboot: Restarting system



** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1928200

Title:
  Prompt error message "Failed to unmount /oldroot" when shutdown or
  reboot

Status in OEM Priority Project:
  Confirmed
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [impact]

  root fs is not cleanly unmounted on shutdown

  [test case]

  create a file in /etc/binfmt.d/TestFormat.conf with the following
  content:

  :TestFormat:M::XX::/bin/true:F

  reboot the system, and then shutdown or reboot again, and watch the
  serial console for the error message:

  sd-umount[1334]: Failed to unmount /oldroot: Device or resource busy

  [regression potential]

  any regression would likely cause problems on shutdown and/or reboot,
  or may cause problems with unmounted root fs on shutdown/reboot

  [scope]

  this is needed only for f

  this is fixed upstream with PR 15566 which is included in v246, so
  this is fixed already in g and later

  this isn't reproducable on b

  [original description]

  On ubuntu 20.04, with latest kernel and systemd, it will show error on
  ThinkPad X1.

  sd-umount[1334]: Failed to unmount /oldroot: Device or resource busy

  systemd 245.4-4ubuntu3.6
  kernel: 5.8.0-53

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