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I'm running a fresh install of Kubuntu 20.04. Every time I reboot, it hangs for several minutes with the last line shown as:

[ OK ] Reached target reboot.

Several minutes later, it finally proceeds to:

sd-umoun[29198]: Failed to umount /oldroot: Device or resource busy
sd-umoun[29199]: Failed to umount /oldroot/dev/pts: Device or resource busy
sd-umoun[29200]: Failed to umount /oldroot/dev: Device or resource busy
sd-umoun[29201]: Failed to umount /oldroot/sys: Device or resource busy
shutdown[1]: Could not detach DM /dev/dm-2: Device or resource busy
shutdown[1]: Could not detach DM /dev/dm-0: Device or resource busy
shutdown[1]: Failed to finalize file systems, DM devices, ignoring
reboot: Restarting system

And then at last it finally reboots. I found a similar issue here, but it has no solution (he said he just reformatted & reinstalled - and my Kubuntu was not an upgrade from a previous version, per that post). Another similar question here has no answer, but also doesn't mention any issue wit hanging - I'd be happy to disregard the message if it didn't seem (?) to be the cause of my agonizingly slow reboots. Search as I might, I can't figure out why it's doing it or how to get it to reboot "normally." Any help would be greatly appreciated.

J23
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2 Answers2

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It sounds like you've got LVM setup which makes things complicated. The "Failed to umount /oldroot" is an issue I do not have on my Ubintu 20.04 desktop system and therefore am unable to help you with. It is not related to LVM either.

LVM setup had hit me we with "Could not detach DM /dev/dm-0: Device or resource busy" error message on shutdown when I upgraded from 18.04 to 20.04. Turned out that my "ubuntu" VG information did not match DM setup after upgrade. Fixed it with vgck command as follows:
sudo vgck --updatemetadata ubuntu
You are to replace "ubuntu" with VG name matching your setup of course.

Lex Ross
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  • Thanks for the answer! After hours & hours & hours, I ended up figuring out a solution...which, oddly, was as simple as running Bleachbit. As to why this actually fixed it, I have no idea tho. Upvoted yours (& will post my solution now) – J23 Oct 22 '20 at 20:09
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This is a "how I fixed it" answer, but note that I never actually figured out why it was happening. If someone has a clearer idea, feel free to post.

Ultimately, the solution was as simple as:

  • Launch bleachbit (as root)
  • Select everything except Vim swap files across the system, Vim swap files under user profile, free disk space, free memory.
  • Run it

Done. There is now zero lag on reboot. Note that it does actually still show (some of) the messages above, so it seems likely my original post was actually mixing up two distinct issues (i.e. it was lagging for a different reason than the message made it appear). But thanks to this this answer on Reddit, I was able to get reboots working properly again & I'm satisfied with that.

J23
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