![]() If the install locations/drives are configuration - driven, and one of these locations can't be reached, then somehow a mismatch has arisen between that configuration data and reality. All that the update needs to do by default is put each part where the current parts are, because obviously that worked. This is actually still a bit of a mystery to me. Ideally, failure to do this should cause grub installation to fail, and the system should be reverted to a safe state. The root cause of the problem is that the grub update has not ensured that both parts have been updated. I would have expected the second, but the grub build system is a work of considerable art, so I don't know :). It's not 100% clear to me if grub_calloc belongs in the second, larger part or the first. The visible, run-time problem occurs when these parts are not aligned, and the function grub_calloc is not supplied. These parts must be aligned - neither part must require any functionality from the other part which is not actually there. But for most of it's functionality, it needs the second part. ![]() The first, most basic, part is the part that is started on bootup. ![]() On 'non-UEFI' systems, grub is installed in two separate parts. OK, thanks to lots of people ! Here's what I think I now understand. Is my best bet just to boot from a live CD and see if I can roll back the update to grub somehow? I noticed that this update also included 'firmware', not sure if that could be related. To me, 'symbol not found' implies some sort of build error with the grub package, but I don't really know how grub works. I'm dropped into the 'grub rescue' shell, but have no idea what to do there that might be useful. Just ran the latest batch of updates on 20.04 (Xubuntu), and now I'm getting a GRUB error: symbol 'grub_calloc' not found To configure GRUB so the menu is always displayed, even after a normal startup, see. The GNU GRUB menu will continue to be displayed automatically on each boot until a normal startup of Ubuntu completes. NOTE 2: If you reboot, there is no need to hold the Shift key in step 3. NOTE 1: If you have Ubuntu Quantal (12.10) or earlier, omit step 4 (the recovery mode menu items are displayed on the top-level menu). (This must be done following step 8 so that /etc/mtab is writable.) Alternatively, you could try selecting " Enable networking" in step 7, though this has been found to cause the system to hang (see ). If you have /home, /boot, /tmp, or any other mount point on a separate partition, you can mount them with the command mount -all To mount it read/write, enter the command mount -o remount,rw / Press Return with this option highlighted. One of the options (you may need to scroll down to the bottom of the list) will be " Drop to root shell prompt". Press Return and your machine will begin the boot process.Īfter a few moments, your workstation should display a menu with a number of options. ![]() Select the line ending with " (recovery mode)", probably the second line, something like: Ubuntu GNU/Linux, with Linux 3.8.0-26-generic (recovery mode) Select the line which starts with " Advanced options". (If you see the Ubuntu logo, you've missed the point where you can enter the GRUB menu.) With UEFI press (perhaps several times) the Escape key to get grub menu. With BIOS, quickly press and hold the Shift key, which will bring up the GNU GRUB menu.(During this time you will probably see a logo of your computer manufacturer.) Note: UEFI fast boot may be too fast to give time to press any key. Wait until the UEFI/BIOS has finished loading, or has almost finished.If booting into recovery mode does not work you can still use your installation CD (if it is a live cd) as described in LivecdRecovery. ![]() You are then logged in as root (the superuser) and can repair your system using command line tools. This mode just loads some basic services and drops you into command line mode. If your system fails to boot for whatever reason, it may be useful to boot it into recovery mode. ![]()
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