cannot find a device for / (is /dev mounted?)

[fabolous_gen2]

A few days ago i wanted to update my kernel as usual, but

[alamahant]

Are you trying to update grub from within a chroot?
Is selinux running in permissive mode?
If you make changes to an selinux system from a chroot then you need to relabel the filesystem in the next boot.
How many btrfs pools do you have?
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[fabolous_gen2]

1. When i update grub from chroot it works perfectly fine and i can boot into the new kernel.
The error occures when i am not in a chroot.
2. I have selinux not enabled. (my profile is: default/linux/amd64/17.1 (stable))
3. I am not sure about this one. As far as i understand btrfs pools are kind of like a RAID and i definitely dont have a RAID system.

This is my fstab file for reference:

[alamahant]

It seems to me you have not installed grub.
Something like

[fabolous_gen2]

I couldn’t reinstall grub due to the same error as when trying to update grub.
In my desperate tries to fix this problem I unmerged grub and wasn’t able to merge it ever since.
Instead i got a few new error messages, that all look like this:

[fabolous_gen2]

Ok i wondered why i couldn’t merge grub so i created a new partition and made a new minimal, side by side gentoo install.
Then i fixed all filesystems and UUID’s and (both) fstab files.
And in my new install (where I was able to merge grub) i edited /boot/grub/grub.cfg by hand and added a second entry which boots into my old install.

This setup is actually pretty neat, but I wish I could manage grub from my main install.

[papu]

i am suffering that problem from 2 days ago, and i can't undestand what are happening.

are you using kernel 6.7.0?

like fabolous_gen2 now [grub-mkconfig -o /boot/grub/grub.cfg gets all time the /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?) message.

but if i launch inside chroot all it's ok.






fstab

[papu]

with kernel < 6.7.0 grub works fine again!

may be a problem with 6.7.0?
see screen shots below

https://i.imgur.com/LqVuAQ3.png 6.7.0 don't works

https://i.imgur.com/EaRB8EM.png 6.6.9 works
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"~amd64" --cpu 7700 non-x --DDR5 2x16GB 6000MHz --gpu RX 470

[eeckwrk99]

papu,

Is this with sys-boot/grub 2.12? There were a couple of threads these last few days from users having issues with this specific -testing- version.

[papu]

[fabolous_gen2]

i can confirm the same behavior as @papu
only kernel versions >=6.7.0 produce this error

Is this because of nvme or btrfs?

[papu]

[fabolous_gen2]

Sorry for late response. I have as good as no time at the moment but i see if i can spare some over this week.

[cc68]

I have excactly the same problem with Kernel 6.7.0, also no initrd

Seems to be a general problem. One system is with efi boot other with MBR/GPT, issue is with both.

[GDH-gentoo]

Could any of the affected people also post the output of grub-probe --verbose --target=device / when booting with a 6.7 kernel and when booting with a 'good' kernel? If the kernel is to blame, I expect the "error: cannot find a device for / (is /dev mounted?)" message in the first case, and a normal output in the latter. The error mensaje about device.map that the OP posted seems strange to me in this context.

The code that seems to fail is function grub_guess_root_devices() in grub-core/osdep/unix/getroot.c. Called from probe() here:

util/grub-probe.c

[cc68]

on a system with kernel 6.5.0

[GDH-gentoo]

Ah, seeing the whole output, the "info: cannot open `/boot/grub/device.map': No such file or directory" message is just informational, the command actually works and prints "/dev/sda3" for kernel 6.5.0, and fails with "error: cannot find a device for / (is /dev mounted?)" for kernel 6.7.0.

Could someone affected install dev-util/strace and post the output (on a pastebin site if necessary) of strace grub-probe --target=device / 2>&1 with the 6.7 kernel? Without the --verbose this time.
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[cc68]

I did the strace, it is temporarily available here:

https://docs.google.com/document/d/1BjDJLrTGTH4IFX99ZTUTF5v6aguqBDDGFEzlKGexiG4

[papu]

kernel 6.7.0

C_MESSAGES=C.utf8 strace grub-probe --target=device / 2>&1
https://paste.gentoo.zip/RqQadznw

LC_MESSAGES=C.utf8 grub-probe --verbose --target=device /

[GDH-gentoo]

[papu]

kernel 6.6.12

[GDH-gentoo]

[fabolous_gen2]

Thank you so much for looking into this.

FYI: My root device is not /dev/nvme0n1p3 it's /dev/nvme1n1p3
Why is this even hardcoded in the kernel?

[pietinger]

[GDH-gentoo]

It's not hardcoded in the kernel. It should give different pathnames for different computers.

"ioctls" are interfaces that the kernel exposes to userspace programs through one system call (see man 2 ioctl if you are curious). grub-probe makes use of some of the Btrfs-specific ones if it finds out (by reading /proc/self/mountinfo) that the pathname it is given is the mountpoint of a device with such a filesystem.

One of these ioctls, BTRFS_IOC_DEV_INFO, seems to have changed behaviour and affect grub-probe. Seemingly for one specific corner case:

• The rootfs is Btrfs.
  
• The rootfs is mounted without an initramfs.

I want to post a small C program based on GRUB's code that readers can build and run to test their kernels. I'll try to do that when I come home after work.

EDIT: It doesn't matter where kernels are, grub-probe --target=device / is called unconditionally.
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