How to Fix a Grub Boot Error: "Symbol 'Grub_Calloc' Not Found

Using Linux Mint 19.3 bios grub setup in a simple 2 partition installation.

After GRUB2 update the machine crashed on reboot and entered rescue mode.

error: symbol 'grub_calloc' not found    

To restore GRUB I booted into Linux Mint 19.3 Live USB stick and issued the following commands in the terminal:

sudo mount /dev/sda1  /mnt    
sudo grub-install --root-directory=/mnt/  /dev/sda    

On reboot the desktop showed up nicely.

I was in the same boat as Rick N. 2 disks but they weren't in RAID. I used this tool

I found that tool from the Ubuntu Help page

It appears to have installed some GUI features that weren't there before (this system has been CLI-only for as long as I can remember) but I'm running again, which is the important part.

Thanks to the others, here, for the guidance.

This is some of the work we did fixing this on our Azure Ubuntu 18.04 servers

Problem appears to be a failed attempt to upgrade grub. Problem happens with an unattended reboot after a security upgrade.

We then found these instructions from a comment posted on the Ubuntu bug for this problem:

Note that I modified this slightly and below is my modified version that I mention in a later comment on the bug( )

For Azure users (the same should work in any cloud, with small changes) that end up here while looking for this bug, the steps to recover are:

Deploy a recovery VM using AzCli or just attach a copy of the affected OS vm disk to a rescue VM. Once done, connected to rescue VM and:

$ sudo su -
# lsblk <-- this will identify the attached disk, usualy /dev/sdc, but can be /dev/sda or /dev/sdb
# mkdir /rescue
# mount /dev/sdc1 /rescue <-- this assumes /dev/sdc is the attached data disk
# for fs in {proc,sys,tmp,dev}; do mount -o bind /$fs /rescue/$fs; done
# cd /rescue
# chroot /rescue
# grub-install /dev/sdc <-- this assumes /dev/sdc is the attached data disk
# exit
# cd /
# for fs in {proc,sys,tmp,dev}; do umount /rescue/$fs; done
# umount /rescue
# rmdir /rescue

Now you should be able to swap back the repaired disk to affected VM.

First attempt at a fix

We found the following Azure documentation links useful:

Ok, step by step:

Deploy a recovery VM

What sort of VM is that? Attempted creating a regular Ubuntu 18.04 LTS VM. This is what you want - to create a recovery VM that matches the servers that are broken

All normal except for connecting to an existing disk. Looks like you can't attach to a disk unless you first somehow move it from another machine (detach it) first.

attach a copy of the affected OS vm disk to a rescue VM.

To create a copy, you can take a read only snapshot of the disk and then create a new Managed Disk based on the snapshot.

The only disk you need a snapshot of is the OS disk, not the data disk.

You can create the recovery VM without a data disk, just the OS disk that automatically gets created.

You can then add the Managed Disk OS snapshot to the recovery VM as a data disk.

Then you can log into the recovery VM and follow the steps above.

All the steps completed without error - we could copy and paste the exact messages

The critical line is running grub-install you should see the following:

root@recoveryVM:/# grub-install /dev/sdc
Installing for i386-pc platform.
Installation finished. No error reported.

Then log out and stop the VM.

You can then go into the broken VM and under the Disks section of the VM select 'Swap OS Disk'.

Reddit mini thread explaining the mounts required: