After I migrated a local VMware Player virtual machine to a QEMU/KVM virtual machine (which worked surprisingly well and with improved performance!), I ran into an apt error a few weeks later.
The mentioned virtual machine runs Linux Mint with a Cinnamon Desktop and after running the system updates, the following error showed up in the GUI:
A manual apt-get dist-upgrade confirmed the error:
ck@mintvm:~$ sudo apt-get dist-upgrade
[...]
Errors were encountered while processing:
shim-signed
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install. Trying to recover:
Setting up shim-signed (1.51.4+15.8-0ubuntu1) ...
Unknown device "/dev/disk/by-id/*": No such file or directory
mount: /var/lib/grub/esp: special device /dev/sda2 does not exist.
dpkg: error processing package shim-signed (--configure):
installed shim-signed package post-installation script subprocess returned error exit status 32
Errors were encountered while processing:
shim-signed
The most interesting information: The post-install script of the shim-signed package somehow wanted to access /dev/sda2 - which does not exist anymore since the VM was migrated (this would now be /dev/vda2):
ck@mintvm:~$ blkid
/dev/vda2: UUID="D3A2-0E8E" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="d86e6df3-d66a-46ad-bbab-a535d220eb0c"
/dev/vda3: UUID="23d9573c-3c80-442c-8658-1d4bf6595c60" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="423655c6-49ad-46e1-9d0d-1291739ca743"
Somewhere in the system a config must still contain a reference to the original /dev/sda disk. But where?
Obviously the first place I looked at was /etc/fstab, but the entries are using the UUID of the partitions:
ck@mintvm:~$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/sda3 during installation
UUID=23d9573c-3c80-442c-8658-1d4bf6595c60 / ext4 errors=remount-ro 0 1
# /boot/efi was on /dev/sda2 during installation
UUID=D3A2-0E8E /boot/efi vfat umask=0077 0 1
/swapfile none swap sw 0 0
And even though the VM was migrated from a VMware Virtual Machine to a KVM/QEMU VM, the UUIDs remain the same (see blkid output above). The machine wouldn't boot either if this wasn't the case.
A grep search inside /etc/ did not reveal any hits (besides the comment in /etc/fstab).
The mentioned post-install script (/var/lib/dpkg/info/shim-signed.postinst) did not contain any hard-coded /dev/sda2 entry either. Where is this still configured if not within /etc/?
After some research I came across a very helpful question on Ask Ubuntu, where the OP basically ran into the same problem. The answer pointed to /var/cache/debconf/config.dat. As it turns out, this file does indeed contain a reference to the old /dev/sda2:
root@mintvm:~# grep sda2 /var/cache/debconf/config.dat
Value: /dev/sda2
Value: /dev/sda2, /dev/vda2
Taking a closer look reveals these entries inside the file:
Name: grub-efi/install_devices
Template: grub-efi/install_devices
Value: /dev/sda2
Owners: grub-common, grub-pc
Flags: seen
Variables:
[...]
Name: grub-efi/install_devices_disks_changed
Template: grub-efi/install_devices_disks_changed
Value: /dev/sda2, /dev/vda2
Owners: grub-common, grub-pc
Flags: seen
Variables:
The first entry (grub-efi/install_devices) still refers to /dev/sda2 as value. The second entry (grub-efi/install_devices_disks_changed) correctly identifies the newer /dev/vda2.
As there is no longer any /dev/sda drive around, let's get fully rid of it and replace /dev/sda2 by /dev/vda2:
root@mintvm:~# sed -i "s/sda2/vda2/" /var/cache/debconf/config.dat
Note: A closer look at the shim-signed postinstall script confirms that this debconf config.dat file is indeed read and therefore uses information/values from that file.
After the change in /var/cache/debconf/config.dat, let's try the package upgrade once more:
root@mintvm:~# apt-get upgrade
apt-get upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up shim-signed (1.51.4+15.8-0ubuntu1) ...
Unknown device "/dev/disk/by-id/*": No such file or directory
Installing grub to /boot/efi.
Installing for x86_64-efi platform.
grub-install: warning: EFI variables cannot be set on this system.
grub-install: warning: You will have to complete the GRUB setup manually.
Installation finished. No error reported.
And finally this ran through correctly! Problem fixed!
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