Ubuntu: Failed to get canonical path of /cow


I am trying to install Ubuntu 12.10 for quite some time, and passing hurdles one by one. Now I am in a situation as follows.

I have got a PC and 10 GB HDD which will be totally dedicated to Ubuntu so no option of Wubi and dual boot.

I was trying to install from DVD, but it is getting stuck at "Out of frequency" error. So I had to adapt for USB boot option. But my PC is USB non bootable, so workaround is "Plop Boot Manager". So I am doing the installation procedure as follows:

  1. starting from a CD drive which is having plop installed.
  2. opting for for USB boot in plop options.
  3. booting begins from USB.
  4. monitor eventually gives "out of frequency" error
  5. press Shift+Alt+F1 to get the terminal.
  6. open the grub with sudo nano /etc/default/grub.
  7. do necessary changes.
  8. sudo update-grub.

Now here I am getting error as follows:

/usr/sbin/grub-probe:error:failed to get canonical path of /cow.  

My system is

P4 3.06 GHz, 1 GB ram , 10 GB HDD without an OS, monitor CRT lg StudioWorks (7 years old). Mobo Mercury P4 266a NDMx (865 equivalent). The whole system is perfectly in working condition under XP, but it is USB non bootable, and all other devices working perfectly.

What should I do next?


After booting from the 14.04 live CD I was able to work around this problem by running update-grub chroot'ed to the grub partition. How you do that depends on what is on the grub partition. (Substitute /dev/sda1 in the below recipes with whatever partition you installed grub on. All commands as root.)

If Your Grub Partition Contains A Full OS Install

Ubuntu 14.04

mount /dev/sda1 /mnt  chroot /mnt  update-grub2  

Ubuntu 16.04

mount /dev/sda1 /mnt  for dir in /dev /dev/pts /proc /sys /run; do      mount --bind $dir /mnt$dir  done  chroot /mnt  update-grub2  

If Your Grub Partition Only Contains Boot Files

In my case the grub partition was a stand-alone boot partition with no system installed, so I had to bring in most of the system to the chroot environment first:

mkdir /mnt/chrootdir  mount /dev/sda1 /mnt/chrootdir  for dir in proc dev sys etc bin sbin var usr lib lib64 tmp; do      mkdir /mnt/chrootdir/$dir && mount --bind /$dir /mnt/chrootdir/$dir  done  chroot /mnt/chrootdir  update-grub2  # inside chroot  


Find your drive that's supposed to boot with



parted -l  


fdisk /dev/sda  

And type p to list the partitions, look for type 83.

(If you've got Fedora you might have to use the commands "vgs" and "lvs" and if you've got mdraid you might have to "cat /proc/mdstat" or mdadm -A --scan or insmod raid1 or insmod raid5 and then mdadm -A --scan) and you will use /dev/md0 or /dev/mapper/my-vg instead of /dev/sda

then try mount it

mkdir /mnt  mount /dev/sda1 /mnt  cd /mnt  ls -l  

Is this your drive? Cool!

grub-install --recheck --root-directory=/mnt /dev/sda   

(Or whichever /dev drive your root is, with it's mounted path)

grub-install --recheck --root-directory=/mnt /dev/sda -f  

(Force it if it doesn't like your partitions.)

Now it should boot into grub, and you can use the grub commands to boot up, after rebooting and selecting the right boot drive from the BIOS Setup, or by pressing ESC or F12 depending on your BIOS and whether you are quick enough, then at the Grub prompt:

insmod linux  ls  root=(hd0,1)  linux /boot/vmlinuz root=/dev/sda1  initrd /boot/initrd  boot  

Or, hopefully you've still got an intact grub.cfg file... or maybe this will work:

grub-mkconfig -o /mnt/boot/grub/grub.cfg  


Revised solution based on code above

The solution from above will not work totally without problems because it mounts the boot partition into the / (root) of the file system. That makes grub complain that /boot does not exist, of course. This will fix that problem:

mkdir /mnt/chrootdir  mkdir /mnt/chrootdir/boot  mount /dev/sda1 /mnt/chrootdir/boot  for dir in proc dev sys etc bin sbin var usr lib lib64 tmp; do mkdir /mnt/chrootdir/$dir && mount --bind /$dir /mnt/chrootdir/$dir ; done  chroot /mnt/chrootdir  update-grub2  # inside chroot  

As you see i also removed the line breaks so that it is easier to execute for everyone.

Another (simpler) solution

If you keep having problems getting it to work you should look to copy the /boot partition onto the / (root) partition. For that start your system with the Ubuntu live boot dvd and open the terminal. Inside it type:

sudo su  fdisk -l  

To find out which partitions you have. In my case sda1 is my /boot partition which is about 250MB large and an sda5 which is about 500GB. I use these values in the commands below:

mkdir /mnt/boot/  mount /dev/sda1 /mnt/boot/    mkdir /mnt/root/  mount /dev/sda5 /mnt/root/    cp -R /mnt/boot/ /mnt/root/boot/  

Set the bootable flag for the data partition and remove it for the boot partition:

fdisk /dev/sda  b -> 1 (unset the bootable flag for the first partition)  b -> 5 (set the bootable flag for the fifth partition)  w -> write changes to the MBR  

Your computer will now look inside the sda5 for the boot files. Time to do the chrooting again, this time with some required folders needed for grub and which are generated by your Ubuntu live disc already:

mkdir /mnt/chrootdir/  mkdir /mnt/chrootdir/dev/  mkdir /mnt/chrootdir/proc/  mkdir /mnt/chrootdir/sys/    mount /dev/sda5 /mnt/chrootdir/  mount --bind /dev/ /mnt/chrootdir/dev/  mount --bind /proc/ /mnt/chrootdir/proc/  mount --bind /sys/ /mnt/chrootdir/sys/    chroot /mnt/chrootdir/    grub-install /dev/sda  

Installation finished. No error reported.

If you do not see a message that the grub.cnf file is generated then also run the update command:

update-grub2 /dev/sda  

Now you can safely reboot and see the well known boot menu appear again.

This solution was the only one which was working for me after migrating from a physical server to a virtual machine. I hope someone finds this useful!


I know, it's a old problem, but I had the same troubles today with the actual version of mint-linux (ubuntu-based). I found a very simply solution! :-) Take off the internet-connection during the first installation. This stop loading of a non compatible grub2. Make the update of all after installation has finished.


It is the update-grub command which will give you the error when using it from a live cd. I faced with a similar situation when i was doing a grub rescue. The problem you have is that update-grub and grub-install commands do not work directly under live cd (I don't know why). So, you have to go to /usr/sbin where the commands are located and execute them from there (i.e ./update-grub).

Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
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