arch-chroot and error with umount -l /mnt/gentoo/dev

[st834]

Hello, this is not a description of the problem, but just a question for a short answer to which I would be grateful.

Why, when, during installation, I enter a new system using an arch-chroot script (https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Base), then when I exit it and execute the command (https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Bootloader):

[ali3nx]

Often umount -l may hang or perhaps single directory unmount may not succeed. that behaviour is just consequential functional quirk that is what it is.

If you try using

[st834]

Thank you very much for your answer.

umount -l works stably even for one directory when /proc, /sys, /dev, /run mounted manually and does not work stably when they are mounted via arch-chroot script. The command unmounts two/dev/shm/and dev/pts file systems.

Are there differences in mounting methods (arch-chroot and manual) that lead to different umount -l behavior?

[ali3nx]

whether you've used arch-chroot or an arch livecd last I used one I've had similar experiences with chroot subdirectories not single directory unmounting while booted from many livecd iso's not limited to arch or having used arch-chroot.


livecd's are fantastic but have functional behaviour quirks that a complete linux distro system install doesn't usually exhibit as commonly. Livecd's are considered temporary in some ways. I usually do gentoo bulds using a fully functional linux distro install as a preference when i'm able to avoid using a livecd for long duration's

umount --lazy is essentially a more polite attempt to unmount a directory. for example if you kill a specific process

[st834]

Thank you for your answer.

I don't use arch livecd, Gentoo Handbook says

[Hu]

How exactly does arch-chroot create its mounts? If it is using a private mount namespace, they would all vanish when you exit.

[st834]

hello, I found the script here: https://gist.github.com/bhelm/65283c37a0cb585089041214002df4f7 , the same is on livecd Gentoo.

as I understand it, using proc and dev as an example, they are mounted like this:

[st834]

I think I figured it out, these file systems will be unmounted automatically when I exit chroot. this is done through the exit trap:

[teika]

When not mounted, the error message is this:

 $ umount /tmp/foo/
 umount: /tmp/foo/: not mounted.

My guess is that it's because the namespace is separated by unshare:

[Hu]

That use of unshare only unshares the pid namespace, but not the mount namespace, so you can ignore it for the purpose of determining when mounts are created and destroyed. Building complicated chroots, and automatically destroying them on exit, is a great use case for unsharing the mount namespace, so I find it a bit surprising that this script would use unshare (thereby depending on its presence), and not make use of a mount namespace.

[teika]

Then maybe this part?

[Hu]

If they use that part, yes. I looked at the upstream repository earlier, but since the script is stored as a template to be modified at install time, I did not try to follow its logic.