Cannot update grub with paramters on live USB

Question

I have booted from a live USB ("Try Ubuntu"), that also has a persistent option set (I used LiLi to create one) to do some tests for this pcie hotplug issue I'm having.

I'm trying to test some boot paramaters (like in this question) by doing this

sudo nano /etc/default/grub
sudo update-grub

The problem is that that last command gives me this:

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

It looks like /cow is the file-system that is mounted on /, according to:

:~# df
Filesystem     1K-blocks    Used Available Use% Mounted on
/cow             4056896 2840204   1007284  74% /
udev             1525912       4   1525908   1% /dev
tmpfs             613768     844    612924   1% /run
....

Is there a way for me to run update-grub?

Answer 1

I found your question while searching how to fix my grub setup after a partition resize from a live cd.

It requires to execute update-grub, and I got the same failed to get canonical path of /cow error message.

I followed this procedure, and I forgot to use the chroot and got the error message.

After the chroot it just works.

I don't know how the live usb works, but it is probable that you have to chroot to the live usb partition to be able to run update-grub properly.

Hope that helps.