[CentOS] CentOS 7 cloned VM cannot boot

Fri May 5 17:34:04 UTC 2017
Gianluca Cecchi <gianluca.cecchi at gmail.com>

Il 05 Mag 2017 19:30, "Nikolaos Milas" <nmilas at noa.gr> ha scritto:

On 5/5/2017 3:45 μμ, Gianluca Cecchi wrote:

BTW: see also this paragraph in the provided RH EL link:
> 24.7.3. Resetting and Reinstalling GRUB 2
> But i think is not your problem....

Yes, I have done that, without change in behavior.

Also, after changing partitions flag does your fdisk command reflect the
> change?


Is the error during boot the same as the one provided in your first e-mail?


One final thing. When I had to change boot settings, I made different steps
> in choot environment in respect of the indication inside the image you
> sent.
> Specifically
> Verify if your boot partition is already mounted under /mnt/sysimage/boot
> in your current environment

Yes, it is:

sh-4.2# df -h
Filesystem               Size Used  Avail Use%  Mounted on
/dev/mapper/live-rw      2.0G 1.1G   930M   54% /
devtmpfs                 979M    0   979M    0% /dev
tmpfs                   1001M 4.0K  1001M    1% /dev/shm
tmpfs                   1001M 8.3M   993M    1% /run
tmpfs                   1001M    0  1001M    0% /sys/fs/cgroup
/dev/sr0                 680M 680M      0  100% /run/install/repo
tmpfs                   1001M 300K  1001M    1% /tmp
/dev/mapper/centos-root   18G 1.5G    16G    9% /mnt/sysimage
/dev/vdal                497M 192M   306M   39% /mnt/sysimage/boot
/tmpfs                  1001M    0  1001M    0% /mnt/sysimage/dev/shm

If it is mounted on another mount point in your live env go and umount it
> and run
> mount /dev/vda1 /mnt/sysimage/boot

Didn't need to.

> chroot /mnt/sysimage

OK, I did so:

sh-4.2# chroot /mnt/sysimage

when you are in chrooted environment, probably you don't have special files
> for vda and vda1 because they are dinamically created;
> verify with
> ls -l /dev/vda*

It seems I do have such files:

bash-4.2# ls -la /dev/vda*
brw-rw----.    1  root disk 252, 0 May 5 16:49 vda
brw-rw----.    1  root disk 252, 1 May 5 16:49 vdal
brw-rw----.    1  root disk 252, 2 May 5 16:49 vda2

If this is the case, go and create them
> mknod -m 660 /dev/vda b 253 0
> mknod -m 660 /dev/vda1 b 253 1

Didn't need to.

at this point
> grub2-install /dev/vda
> and let see the output of the command and its exit code

As usual:

   bash-4.2# grub2-install /dev/vda

   Installing for i386-pc platform.
   grub2-install: error: unknown filesystem.

at this point exit chrooted environment (exit)
> umount /mnt/sysimage/boot
> reboot and see if anything changes

Didn't do it,  because grub2-install above failed, so nothing changed.

I am very puzzled with "unknown filesystem".

Thanks for your time and help! I am looking forward to reaching a solution!

All the best,


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CentOS at centos.org

Your /mnt/sysimage/boot is under tmpfs not real disk...
Try to unmount it and mount the vda1 device instead and then follow the
other steps...