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**oshunluvr** · Jan 03, 2016, 07:58 AM

Lots of data in there, but at first glance I have a question: Did you use the default install setup for btrfs when you installed (K)Ubuntu? What I mean is; when installing - you used the installer and selected a btrfs file system as the target to install to?

If yes, the default (K)Ubuntu btrfs install creates two subvolumes on the target btrfs partition: @ for / and @home for /home. This means that, for example, the file system on 821f7ab0-4351-45f1-b870-1a4b33db1b5c contains these two subvolumes - @ and @home. Therefore, grub is not finding the configfile grub.cfg because it's in /@/boot/grub/ not /boot/grub/. Your 40_custom grub stanzas need to reflect the subvolume /@/ in the configfile statements.

If you did something non-standard during install, please detail what.

After booting, the two subvolumes are transparent to you because in your fstab mounts the subvolumes are stated as options like this: subvol=@. In fact, you should see two separate fstab lines that are nearly identical for both the root and home mounts - the only differences being the mount points and subvolume names.

**SimonAndric** · Jan 04, 2016, 05:46 PM

Originally posted by oshunluvr View Post

Lots of data in there, but at first glance I have a question: Did you use the default install setup for btrfs when you installed (K)Ubuntu? What I mean is; when installing - you used the installer and selected a btrfs file system as the target to install to?

If yes, the default (K)Ubuntu btrfs install creates two subvolumes on the target btrfs partition: @ for / and @home for /home. This means that, for example, the file system on 821f7ab0-4351-45f1-b870-1a4b33db1b5c contains these two subvolumes - @ and @home. Therefore, grub is not finding the configfile grub.cfg because it's in /@/boot/grub/ not /boot/grub/. Your 40_custom grub stanzas need to reflect the subvolume /@/ in the configfile statements.

If you did something non-standard during install, please detail what.

After booting, the two subvolumes are transparent to you because in your fstab mounts the subvolumes are stated as options like this: subvol=@. In fact, you should see two separate fstab lines that are nearly identical for both the root and home mounts - the only differences being the mount points and subvolume names.

Hello!

first let me say, your help is much appriciated, even more so, because IT WORKED! Thank you so much!

By "it worked" i mean, i just had to minimally edit both of my "40_custom" files, to look like this:

plasma 5 (etc/grub.d/40_custom):

Code:

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry 'kde4' {
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root 821f7ab0-4351-45f1-b870-1a4b33db1b5c
configfile [COLOR=#ff0000][B]/@[/B][/COLOR]/boot/grub/grub.cfg
}

and my kde4 (etc/grub.d/40_custom):

Code:

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry 'Plasma5' {
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root 3af2cb3c-34d8-4f4e-94be-4e7138e331de
configfile [COLOR=#ff0000][B]/@[/B][/COLOR]/boot/grub/grub.cfg
}

Let me also say both of my installations i used the default installation BTRFS settings (it means i selected btrfs partitions in the kubuntu installation menu), therefore my fstabs look like this:

plasma5:

Code:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda5 during installation
UUID=3af2cb3c-34d8-4f4e-94be-4e7138e331de /               btrfs   defaults,subvol=@ 0       1
# /home was on /dev/sda5 during installation
UUID=3af2cb3c-34d8-4f4e-94be-4e7138e331de /home           btrfs   defaults,subvol=@home 0       2
# swap was on /dev/sda1 during installation
UUID=d2ad0990-78e3-464e-8ac9-1dc67be49963 none            swap    sw              0       0


# kde4 on /dev/sda6
LABEL=kde4    /media/original/kde4root/               btrfs    defaults 0       1
/media/original/kde4root/@/ /media/fani/kde4/   none  bind     0   0
/media/original/kde4root/@home/ /media/fani/kde4_home/   none  bind     0   0

# disk on /dev/sda7
LABEL=disk    /media/original/diskroot/               btrfs    defaults 0       1
/media/original/diskroot/disk/ /media/fani/disk/   none  bind     0   0

and kde4:

Code:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda6 during installation
UUID=821f7ab0-4351-45f1-b870-1a4b33db1b5c /               btrfs   defaults,subvol=@ 0       1
# /home was on /dev/sda6 during installation
UUID=821f7ab0-4351-45f1-b870-1a4b33db1b5c /home           btrfs   defaults,subvol=@home 0       2
# swap was on /dev/sda1 during installation
UUID=d2ad0990-78e3-464e-8ac9-1dc67be49963 none            swap    sw              0       0
/dev/sdb        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0


# plasma5 on /dev/sda5
LABEL=plasma5    /media/original/plasma5root/               btrfs    defaults 0       1
/media/original/plasma5root/@/ /media/fani/plasma5/   none  bind     0   0
/media/original/plasma5root/@home/ /media/fani/plasma5_home/   none  bind     0   0

# disk on /dev/sda7
LABEL=disk    /media/original/diskroot/               btrfs    defaults 0       1
/media/original/diskroot/disk/ /media/fani/disk/   none  bind     0   0

The only thing which i cannot right now still do is run "grub-install" when i chroot into another instalaltion. I know, now i can simply boot the other installation and "grub-install" from there, but i would like to know in case one day it might come in handy, if i find myself in situation that i cannot access the other installation other way than to chroot in it. Thats also the reason i (for now) wont mark this as solved just yet

so if i do this:

Code:

fani@avatar:~$ sudo mount[COLOR=#ff0000][B] -o subvol=@[/B][/COLOR] /dev/sda5 /media/fani/plasma5

fani@avatar:~$ for i in dev/pts sys proc run; do sudo mount --bind /$i /media/fani/plasma5/$i; done

fani@avatar:~$ sudo chroot /media/fani/plasma5

root@avatar:/# sudo grub-install /dev/sda
Installing for i386-pc platform.
grub-install: napaka: failed to get canonical path of `/dev/sda5'.

then i tried this (without setting the "subvol"):

Code:

fani@avatar:~$ sudo mount /dev/sda5 /media/fani/plasma5

fani@avatar:~$ for i in dev/pts sys proc run; do sudo mount --bind /$i /media/fani/plasma5/$i; done

fani@avatar:~$ sudo chroot /media/fani/plasma5

root@avatar:/# sudo grub-install /dev/sda
Installing for i386-pc platform.
grub-install: napaka: failed to get canonical path of `/dev/sda5'.

same thing.... what am i doing wrong here?

and..again thank you!

nice day

Simon

**oshunluvr** · Jan 05, 2016, 09:57 AM

My setup is different than yours so I can't answer that last part. I see why you might want to do that, but I have no ideas at the moment. You might consider that you're going through more work than really necessary considering the value of skipping a reboot to upgrade grub. Of course, learning how to do it could be useful down the road.

What I do is install ALL my versions and distros to the same btrfs flesystem by changing the default subvolume names to unique names. My btrfs root looks like this:

Code:

stuart@office:~$ ll /mnt/samsung/
total 0
drwxr-xr-x 1 root   root   382 May 28  2015 @Kubuntu_14_04
drwxr-xr-x 1 root   root    48 Jan 25  2015 @Kubuntu_14_04_home
drwxr-xr-x 1 root   root   306 Dec 19 12:47 @Kubuntu_15_04
drwxr-xr-x 1 stuart stuart  86 Jul 27 09:51 @Kubuntu_15_04_home
drwxr-xr-x 1 root   root   248 Dec 19 13:25 @Kubuntu_15_10
drwxr-xr-x 1 root   root    52 Dec 19 13:13 @Kubuntu_15_10_home
drwxr-xr-x 1 root   root   126 Dec 19 12:55 snapshots
drwxr-x--- 1 stuart stuart 732 Nov  3 11:34 @stuart

Then I use a dedicated grub install that uses the grub.cfg of each install to boot. IMO, there's little reason to upgrade grub often as it's not really a security issue.

**SimonAndric** · Jan 08, 2016, 08:25 PM

hello!

im just writing to say i managed to SOLVE it!

the problem was with my "FOR" sentence.... The right way to do it is like this:

Code:

sudo mkdir /mnt
sudo mount -o subvol=@ /dev/sdaX /mnt
[COLOR=#ff0000]for i in /dev /dev/pts /proc /run /sys; do sudo mount -B /$i /mnt/$i; done[/COLOR]
sudo chroot /mnt
sudo grub-install /dev/sdX
sudo update-grub

[COLOR=#ff0000]for i in /dev /dev/pts /proc /run /sys; do sudo umount -B /$i /mnt/$i; done[/COLOR]
sudo umount /mnt
exit

thank you for your help! much appriciated!

nice day!

Simon

**oshunluvr** · Jan 09, 2016, 07:49 AM

Excellent work and thanks for detailing it and your solution.

Announcement

[BTRFS] [GRUB] Problem with GRUB recognizing my two installations

[SOLVED] [BTRFS] [GRUB] Problem with GRUB recognizing my two installations

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