[RESOLVED] No dual boot

[nilsA]

So, after a long time no problem installing, upgrading and running Kubuntu, today I installed Kubuntu alongside WIN10 on a HP Probook 6560b.

Hard disk two partitions (plus two minimal) (sda2) WIN10, (sda4) Kubuntu 24.04.2 LTS. (sda1) and (sda3) are very small and seem to have been created by the cloning program when I transferred the 256 GB original HD with WIN10 to a 500 GB SD disk.

Everything fine, but when I reboot, there is no boot screen, so I can't find WIN10.

How to fix this?

[oshunluvr]

Check /etc/grub.d/30_os-prober and make sure it's executable. Then run "sudo update-grub"

[jlittle]

Check /etc/grub.d/30_os-prober and make sure it's executable. Then run "sudo update-grub"

Before running sudo update-grub, ensure that /etc/default/grub has the line

GRUB_DISABLE_OS_PROBER=false
​

(That variable was changed to come on a new install set to true, as it is was considered a security hole.)

[claydoh]

sda1 is likely your EFI partition, needed and used by both Windows and Linux for housiong their boot loaders. The other may be a Windows recovery partition, in lieu of a restore disk. These often break when re-partitioning and dual booting.



Now, to add to the other suggestions, you can also use a hotkey when powering on to to choose a specific OS instead of the default one set in the BIOS (Kubuntu in your case). On my HP I can get there using the <esc> key or <F9> or <F8>, (can't recall) during the initial HP bootup splash screen. This is useful when there are boot/grub problems or as a fallback, or seldom boot another OS and don't want a grub menu seen at all.

As you aren't seeing a boot menu at all, but still loading Kubuntu, your menu may be set to 'hidden'.
You can check this and change it if necessary in /etc/default/grub

GRUB_TIMEOUT_STYLE=menu is what you want to see.
If it is set as hidden, change it to menu, save, and then run sudo update-grub

Another thing to try, if you like the menu being hidden, is hitting your <f4 key> (or <esc> again) at the right time at the end of your initial boot splash to bring up the grub menu. It isn't always easy or clear when to hit this, and spamming the key might get you to a strange grub edit or commandline screen so I don't usually suggest this.

Now, I have had some systems in the past where the monitors aren't fully powered on and in use at this stage, so this might be an issue as well. Setting a longer timeout in your grub config might help here as well, if the menu is not set as hidden.

[nilsA]

Thank you all for your kind answers!

Now, this happened to solve itself, and I am not sure how/why. As it happened I needed something in the Windows part of the PC, and found it easier to use a WIN10 rescue CD to get in while waiting. The strange thing is, the rescue CD did not boot, but was obviously read - and then the Grub menu was there!