hd1 cannot get C/H/S values

[19henry21]

Hello,

Having a dual boot PC with Windows 10 / Linux Mint 19.3 and using on that PC also a Mint 20.2 external disk, I ran into the problem of not being able to boot the external disk any more (to which I had already transferred important data from the Mint 19.3.)

During my normal startup GRUB let me chose whether I wanted to boot either Windows 10 or Linux Mint 19.3 or Linux Mint 20.2 on the external disk. This does not work any more. I can only boot either Windows 10 or Linux Mint 19.3 but n o t Linux Mint 20.2 on the external disk although it is shown on the startup GRUB screen.

Trying to apply the standard boot repair procedure did not work out. Booting from ATA (whatever that means, but recommended by the boot repair app) was not possible. I ended up with the Linux Mint recovery mode and got the error message: "hd1 cannot get C/H/S values, no such device, you have to start the kernel first".

Hoping that somebody can help me out, I would like to show the current system:

user@user-ThinkPad-T510:~$ sudo fdisk -l
[sudo] Passwort für user:
Festplatte /dev/loop0: 2 GiB, 2147483648 Bytes, 4194304 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop1: 290,1 MiB, 304140288 Bytes, 594024 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop2: 219 MiB, 229638144 Bytes, 448512 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop3: 164,8 MiB, 172761088 Bytes, 337424 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop4: 55,4 MiB, 58114048 Bytes, 113504 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop5: 135,4 MiB, 142016512 Bytes, 277376 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop6: 139,1 MiB, 145883136 Bytes, 284928 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop7: 65,1 MiB, 68259840 Bytes, 133320 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/mmcblk0: 119,1 GiB, 127865454592 Bytes, 249737216 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
Festplattenbezeichnungstyp: dos
Festplattenbezeichner: 0xddf664c4

Gerät Boot Anfang Ende Sektoren Größe Kn Typ
/dev/mmcblk0p1 2048 249737215 249735168 119,1G 83 Linux


Festplatte /dev/sda: 465,8 GiB, 500107862016 Bytes, 976773168 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
Festplattenbezeichnungstyp: dos
Festplattenbezeichner: 0x801c4ce0

Gerät Boot Anfang Ende Sektoren Größe Kn Typ
/dev/sda1 2048 1187839 1185792 579M 7 HPFS/NTFS/exFAT
/dev/sda2 1187840 442849279 441661440 210,6G 7 HPFS/NTFS/exFAT
/dev/sda4 442849280 976771071 533921792 254,6G f W95 Erw. (LBA)
/dev/sda5 * 442851328 976771071 533919744 254,6G 83 Linux


Festplatte /dev/sdb: 3,7 TiB, 4000787029504 Bytes, 7814037167 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 4096 Bytes
E/A-Größe (minimal/optimal): 4096 Bytes / 4096 Bytes
Festplattenbezeichnungstyp: gpt
Festplattenbezeichner: C331BC8A-3620-42E8-A240-8EB9F2CC180F

Gerät Anfang Ende Sektoren Größe Typ
/dev/sdb2 2048 2097029119 2097027072 1000G BIOS boot
/dev/sdb3 2097416192 3940616191 1843200000 878,9G Microsoft Basisdaten
/dev/sdb4 3940616192 5789960191 1849344000 881,9G Microsoft Basisdaten
/dev/sdb5 5789960192 7641352191 1851392000 882,8G Microsoft Basisdaten
/dev/sdb6 7641352192 7743752191 102400000 48,8G Microsoft Basisdaten




Festplatte /dev/mapper/cryptswap1: 2 GiB, 2146959360 Bytes, 4193280 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop8: 99,4 MiB, 104202240 Bytes, 203520 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop9: 99,4 MiB, 104210432 Bytes, 203536 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop10: 290,1 MiB, 304140288 Bytes, 594024 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop11: 95,7 MiB, 100352000 Bytes, 196000 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop12: 219 MiB, 229629952 Bytes, 448496 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop13: 64,8 MiB, 67915776 Bytes, 132648 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop14: 162,9 MiB, 170778624 Bytes, 333552 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop15: 95,7 MiB, 100356096 Bytes, 196008 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop16: 55,5 MiB, 58134528 Bytes, 113544 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/sdc: 14,9 GiB, 15938355200 Bytes, 31129600 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
Festplattenbezeichnungstyp: dos
Festplattenbezeichner: 0xc3072e18

Gerät Boot Anfang Ende Sektoren Größe Kn Typ
/dev/sdc1 240 31129599 31129360 14,9G c W95 FAT32 (LBA)
user@user-ThinkPad-T510:~$ sudo lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 2G 0 loop
└─cryptswap1 253:0 0 2G 0 crypt [SWAP]
loop1 7:1 0 290,1M 1 loop /snap/vault/1958
loop2 7:2 0 219M 1 loop /snap/gnome-3-34-1804/72
loop3 7:3 0 164,8M 1 loop /snap/gnome-3-28-1804/161
loop4 7:4 0 55,4M 1 loop /snap/core18/2066
loop5 7:5 0 135,4M 1 loop /snap/skype/176
loop6 7:6 0 139,1M 1 loop /snap/skype/177
loop7 7:7 0 65,1M 1 loop /snap/gtk-common-themes/1515
loop8 7:8 0 99,4M 1 loop /snap/core/11316
loop9 7:9 0 99,4M 1 loop /snap/core/11420
loop10 7:10 0 290,1M 1 loop /snap/vault/1930
loop11 7:11 0 95,7M 1 loop /snap/poedit/29
loop12 7:12 0 219M 1 loop /snap/gnome-3-34-1804/66
loop13 7:13 0 64,8M 1 loop /snap/gtk-common-themes/1514
loop14 7:14 0 162,9M 1 loop /snap/gnome-3-28-1804/145
loop15 7:15 0 95,7M 1 loop /snap/poedit/30
loop16 7:16 0 55,5M 1 loop /snap/core18/2074
sda 8:0 0 465,8G 0 disk
├─sda1 8:1 0 579M 0 part
├─sda2 8:2 0 210,6G 0 part
├─sda4 8:4 0 1K 0 part
└─sda5 8:5 0 254,6G 0 part /
sdb 8:16 0 3,7T 0 disk
├─sdb2 8:18 0 1000G 0 part
├─sdb3 8:19 0 878,9G 0 part /media/user/A58B-5CA7
├─sdb4 8:20 0 881,9G 0 part /media/user/AF1D-CA10
├─sdb5 8:21 0 882,8G 0 part /media/user/B738-1BEE
└─sdb6 8:22 0 48,8G 0 part /media/user/Home Data 4
sdc 8:32 1 14,9G 0 disk
└─sdc1 8:33 1 14,9G 0 part /media/user/USB DISK
sr0 11:0 1 1024M 0 rom
mmcblk0 179:0 0 119,1G 0 disk
└─mmcblk0p1 179:1 0 119,1G 0 part /media/user/USB STICK
user@user-ThinkPad-T510:~$


My Linux Mint 20.2 system was created big enough to satisfy my future needs and is located on sdb2.
Your assistance to solve the boot problem with my external disk system is very much appreciated.

[AndyMH]

Is your mint 20.2 install on sdb2 an encrypted install?

[19henry21]

No, I learned from previous bad experience and did n o t encrypt it. I also wanted to test Mint 20.2 on an external disk before I switch from Mint 19.3.

[AndyMH]

The reason I asked about encryption was this:

Code: Select all

Festplatte /dev/mapper/cryptswap1: 2 GiB, 2146959360 Bytes, 4193280 Sektoren

I don't use encryption so cannot comment on if this is a problem.

I was also initially confused by the number of loop devices showing in fdisk, but this is due to snaps - which I don't use.

Your original post suggested that you have been able to boot mint from the external drive (sdb). I am surprised because:

Code: Select all

Festplattenbezeichnungstyp: dos

Suggests you are booting mint and windows from sda in legacy mode from a drive with a legacy partition table

While

Code: Select all

Festplattenbezeichnungstyp: gpt

you have a GPT partition table on sdb which implies UEFI boot, but there is no EFI partition on that drive. But you do need a GPT partition table on that drive because it is larger than 2TB (the limit for a legacy partition table).

You do have a EFI partition table on sda, but the fdisk output does not show what flags are set. It may be as a result of installing mint on sda with the 'install alongside' option - it creates a useless EFI partition (a bug*).

Check your BIOS settings, if the T510 is anything like a T430 you will have four options - UEFI only, Legacy only, Both (legacy first), Both (UEFI first). I would expect it to be either legacy only or both (legacy first). You can also check your BIOS boot list - do you have an entry for 'ubuntu' - this would be a UEFI install, probably on sdb - if you select it does it boot?

You can also check, booting LM19.3, in a terminal:

Code: Select all

andy@T432 ~ $ efibootmgr
EFI variables are not supported on this system.

this is a T430 booting in legacy mode. Anything else and you are booting UEFI.

Booting LM19.3 from sda can you mount sdb1 in your file manager? It should appear in the devices panel on the left, probably as something like 1000G volume. Can you see all the files and folders?

My best guess at the moment is that you have LM19.3 installed in legacy mode and you managed to install LM20.2 in UEFI mode.

Note - for future reference post terminal output between code markers (the </> button above the reply window), it makes it easier to read.


* viewtopic.php?f=46&t=326270&p=1855497&h ... l#p1855497

[19henry21]

Thanks Andy, I appreciate your explanations and your patience with a bloody beginner. Perhaps I should study more basics about OS systems in order to understand better. Do you know a good publication for non-IT people?

Let me go to the subject matter: I started with the last remark in your post and found out via the command you had suggested that there is was no UEFI boot system detected. Am I correct to conclude from your remarks that (at best) there should be a Legacy boot system on the dual boot PC and on the external Mint 20.2 disk? Since I did not know how to establish that on my PC, I wanted to start a comparative analysis and approached a friend who also has a dual boot (Windows 10/Linux Mate 19.3) Lenovo T430 PC. He let me test my external Mint 20.2 disk and what a surprise: on his Lenovo T430 PC I could start it without any problem.

At startup a GNU GRUB version 2.02 showed up and displayed

1) the Linux 19.3 Mate
2) the Windows 10
3) the Mint 20.2 Uma disk.

None of the systems started automatically. A click on choice 3 opened the Linux Mint 20.2 system, let me apply my password and everything worked fine. After that we tested 1) and 2) and they also worked fine. My conclusion from that: The problem might have something to do with settings on my Lenovo T510 PC.

Next surprise: When I went back to connect the external Mint 20.2 disk to my Lenovo T510 again, a different GRUB version 2.02 screen showed up than in the past. It only displayed

1) the Linux 19.3 Mate and
2) the Windows 10 system.

Both systems could be started via a click at the relevant part and both worked fine. Only the external Mint 20.2 disk did not show up on the startup screen. Following your recommendation I checked in Linux Mint 19.3 and found that all Windows partitions were shown but not the Mint 20.2 volume.

Another observation: If I did not make a choice between 1) und 2) Linux Mint 19.3 started automatically after a short while. It looks like the GRUB version 2.02 comes up with different screens on different PCs. Can that happen even considering that I always chose a comparable USB port for the external Mint 20.2 disk?

Hoping that I made my comparative observations clear enough, I wonder whether you can make something out of it. Your comments are very much appreciated.

[AndyMH]

Try this bit:

Check your BIOS settings, if the T510 is anything like a T430 you will have four options - UEFI only, Legacy only, Both (legacy first), Both (UEFI first). I would expect it to be either legacy only or both (legacy first). You can also check your BIOS boot list - do you have an entry for 'ubuntu' - this would be a UEFI install, probably on sdb - if you select it does it boot?

Booting LM19.3 you can also, in a terminal sudo os-prober. If LM20 on the external drive is installed in legacy mode (don't think it is, nowhere for the bootloader) it will find it. If it doesn't it suggests that LM20 is installed in UEFI mode. If it does find it, then sudo update-grub should add it to the grub menu for your next boot.

[19henry21]

Thank you, Andy. I did not know how to check the bios setting.

After proceeding as suggested via the command line, I got the following output:

user@user-ThinkPad-T510:~$ sudo os-prober
[sudo] Passwort für user:
/dev/sda1:Windows 10:Windows:chain
/dev/sda2:Windows 10:Windows1:chain
/dev/sdb2:Linux Mint 20.2 Uma (20.2):LinuxMint:linux
user@user-ThinkPad-T510:~$ sudo update-grub
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/50_linuxmint.cfg'
GRUB-Konfigurationsdatei wird erstellt …
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-147-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-147-generic
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-144-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-144-generic
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-20-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-20-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
Windows 10 auf /dev/sda1 gefunden
Windows 10 auf /dev/sda2 gefunden
Linux Mint 20.2 Uma (20.2) auf /dev/sdb2 gefunden
erledigt
user@user-ThinkPad-T510:~$

this sounds like everything is done and o.k. When starting the PC after that update and clicking Linux Mint 20.2 Uma, I however still get an error message saying that the device 0f79e865-7802-4ab1-b592-ab2c0cc3ab1d cannot be found etc.etc. (just like mentioned in the beginning of my post: ...cannot get C/H/S values, load kernel first)

Going via Gparted on Linux Mint 19.3 to /dev/sdb2 I can find the device on which Linux Mint 20.2 is installed in the correct size. The partition info says that it is not mounted and shows the flag: bios grub. Do I have to change that flag and if so how? Or do I have do change anything in my Windows setup? Unfortunately, I don't know how to do it there neither. With your last hints we still advanced in the necessary analysis, didn't we? Thanks so much for your attention.

[AndyMH]

this sounds like everything is done and o.k. When starting the PC after that update and clicking Linux Mint 20.2 Uma, I however still get an error message saying that the device 0f79e865-7802-4ab1-b592-ab2c0cc3ab1d cannot be found etc.etc. (just like mentioned in the beginning of my post: ...cannot get C/H/S values, load kernel first)

Going via Gparted on Linux Mint 19.3 to /dev/sdb2 I can find the device on which Linux Mint 20.2 is installed in the correct size. The partition info says that it is not mounted and shows the flag: bios grub. Do I have to change that flag and if so how? Or do I have do change anything in my Windows setup? Unfortunately, I don't know how to do it there neither. With your last hints we still advanced in the necessary analysis, didn't we? Thanks so much for your attention.

For future reference, when you post terminal output paste it between code markers (the </> above the reply window) - makes it much easier to read, e.g. your last post:

Code: Select all

user@user-ThinkPad-T510:~$ sudo os-prober
[sudo] Passwort für user:
/dev/sda1:Windows 10:Windows:chain
/dev/sda2:Windows 10:Windows1:chain
/dev/sdb2:Linux Mint 20.2 Uma (20.2):LinuxMint:linux
user@user-ThinkPad-T510:~$ sudo update-grub
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/50_linuxmint.cfg'
GRUB-Konfigurationsdatei wird erstellt …
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-147-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-147-generic
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-144-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-144-generic
Linux-Abbild gefunden: /boot/vmlinuz-4.15.0-20-generic
initrd-Abbild gefunden: /boot/initrd.img-4.15.0-20-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
Windows 10 auf /dev/sda1 gefunden
Windows 10 auf /dev/sda2 gefunden
Linux Mint 20.2 Uma (20.2) auf /dev/sdb2 gefunden
erledigt

I think your problem might be the setup on sdb, your external drive. When you try and boot in legacy mode on a drive with a gpt partition table (you need one because of the size of the drive*), grub is normally installed in its own partition. This is called a bios_grub partition. It is 1MB in size and has the flag bios_grub set on it - that is all you don't need to do anything else. You don't have a bios_grub partition on sdb and I think grub is installed in sdb2. For some reason this is okay on a T430 but not on the T510 (an older thinkpad).

The simplest thing is to re-install mint on your external drive:

• copy anything you want to keep off sdb2 (your /partition) because it is going to be overwritten.

• boot LM19.3 and install gparted (from software manager) if not already installed.

• run gparted and create a bios_grub partition on sdb. If you have already used all the drive space, just shrink the last partition to create space. The partition you create only needs to be 1MB in size and set the flag bios_grub on it (when you have created the partition right click on it and 'manage flags'). You don't need to format it. While the partition is better at the beginning of the drive, it should be okay at the end, just slightly slower to boot. Putting it at the beginning of the drive will mean moving all the other partitions = slow to move the data and slightly more risky.

• boot your mint install stick and re-install. Select the 'something else' option. The next screen shows you all your drives and partitions, select sdb2 (your existing / partition) tell it to use it for / and reformat it.

• at the bottom of the screen is a drop-down asking where to put the bootloader. You select the drive, sdb, not a specific partition, the installer will find your bios_grub partition and install grub in it.

• install.

• You will need to re-install any software you have installed.

When you reboot you might find that it automatically boots into your external drive. If so, go into BIOS and make sure that the drive with LM19.3 is at the top of the boot list. Boot LM19.3 and in a terminal sudo update-grub. It should find LM20 on the external drive and add it to the grub menu for the next boot.

Your other alternative is to create your bios_grub partition and then re-install grub. This would save you re-installing mint. It is reasonably straightforward with legacy boot, but I've never done it on a GPT drive with a bios_grub partition. If you want to try this first, ask.

* you normally install linux in legacy mode to a drive with a legacy/msdos partition table, but this option is not available to you because you have a 4TB drive and the max drive size for a legacy partition table is 2TB. You are stuck with GPT.

[19henry21]

Thanks for your input, Andy. For an unexperienced user the first alternative seems to be a real challenge.

So please, if you don't mind, let me still know what to do with the second alternative of creating a bios-grub partition on my current 4 TB external disk.

What I take from this whole exercise is, that obviously using an external disk bigger than 2 TB for a Linux Mint system is not recommendable for somebody who is not experienced in handling boot problems. Should alternative 2 you mentioned not work at all, I am considering setting up a new 2 TB external disk with a 1,2 TB Linux Mint 20.2 system, make a backup of my current 1 TB system partition of the 4 TB external disk and restore this one the new system partition of the 2 TB external disk. All the other data could remain where they are. Only disadvantage: I would have to carry around two external disks, but would avoid having to reinstall all the software on my current disk. What do you think?

[AndyMH]

Can't guarantee that this will work - not tried with a bios_grub partition on a gpt drive.

You still need to create a bios_grub partition. I have see one post online that says it must be at the start of the drive, but not sure I believe that.

Booting LM19.3 as normal, in a terminal:

Code: Select all

sudo mount /dev/sdb2 /mnt 
sudo grub-install --boot-directory=/mnt/boot /dev/sdb

The first command mounts your LM20 / partition at /mnt in LM19.3. The second command installs grub to sdb using the files in the /boot folder of LM20. This command should find your bios_grub partition and install grub into it.

[19henry21]

Thanks Andy for your many hints and explanations.

Since you warned me that alternative 2 of your suggestions might not work out, I took a prudent approach and first made a backup of my sdb2 partition which took a long time to finish. Then I started Linux 19.3 and proceeded step by step with the commands you suggested and got no error messages in between. But ... after having finished, I still could not boot my 4 TB external disk with the Linux Mint 20.2 system.

Next step: I bought a brand new 2 TB external disk and installed Linux Mint 20.2 with the same password I had used on my 4 TB external disk. I chose the size of the Mint 20.2 primary partition a little bit bigger (1.3 TB) than on my 4 TB external disk. Then I restored the backup partition of my 4 TB external disk on the new 2 TB external disk. All of that took ages. Upon startup the Lenovo T510 stil only showed Linux Mint 19.3 and Windows 10 as boot alternatives.

When I booted with F12 however, I could see the Linux Mint 20.2 as one of the available alternatives and booted the 2 TB disk with no problems at all. All the apps worked fine. Out of curiosity I tried the same with my old 4 TB external disk and - what a surprise - it worked too.

I have no idea why all the sudden the old system a n d the new system worked without any problem, as long as I booted them via F12. My guess is that through the new installation something must have inadvertedly been fixed on my Lenovo T510 PC. If you have any idea, please let me know. It might also help the understanding of other users who face similar problems!!