package grub-legacy-ec2 1:1 failed to install/upgrade: installed grub-legacy-ec2 package post-installation script subprocess returned error exit status 10

Thank you for taking the time to file a bug report.

I have tried to reproduce this problem here, but did not succeed. Here's what I did:

1) Launched a Bionic VM using lxd

2) apt update && apt upgrade

3) apt-get -o APT::Status-Fd=4 -o APT::Keep-Fds::=5 -o APT::Keep-Fds::=6 -q -y -o APT::Install-Recommends=true -o APT::Get::AutomaticRemove=true -o APT::Acquire::Retries=3 install server^

This last command is what triggered the problem; I don't think the previous commands from the log are too important.

Everything went fine, including the configuration process of grub-legacy-ec2. In my test system, here is what I saw:

Setting up grub-legacy-ec2 (1:1) ...
Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... Generating /boot/grub/default file and setting the default boot entry to 0
Searching for GRUB installation directory ... found: /boot/grub
Testing for an existing GRUB menu.lst file ...

Could not find /boot/grub/menu.lst file.
Generating /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /boot/vmlinuz-4.15.0-126-generic
Found kernel: /boot/vmlinuz-4.15.0-124-generic
Updating /boot/grub/menu.lst ... done

As you can see, I did not get an error about dpkg not being able to determine the root device. I have also gotten the full log, whereas in your case it appears that the log has been cut. Do you have access to the full output of the "apt-get" command you executed?

It is hard to say for certain, but it seems to me that there might be a local configuration error in your system that is preventing the package from completing its setup.

Since it seems likely to me that this is a local configuration problem,
rather than a bug in Ubuntu, I am marking this bug as 'Incomplete'.

However, if you believe that this is really a bug in Ubuntu, then we would
be grateful if you would provide a more complete description of the problem
with steps to reproduce, explain why you believe this is a bug in Ubuntu
rather than a problem specific to your system, and then change the bug
status back to "New".

For local configuration issues, you can find assistance here:
http://www.ubuntu.com/support/community

[Expired for grub-legacy-ec2 (Ubuntu) because there has been no activity for 60 days.]