Without enter the bios, in some PC you can choose from what device boot, simply with F11 key.
You will prompt for the device you want start from (an usb one or a partition of your PC).
Install Kubuntu without EFI bootloader
If you have, i.g., another linux distro, such as KDE-Neon, and you want add Kubuntu as secondary SO, without changing your EFI, you do this way:
- in Kubuntu (usb iso) menu -> try Kubuntu
- in a terminal (once logged in):
ubiquity -b - this will open the graphical installation tool letting you install Kubuntu without modifying existing EFI
- don’t worry for the warnings (“the system could not start”)
- after rebooting, in KDE-Neon do
update-grub
If you get, with update-grub, an error such this:
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
You can solve adding or uncommenting this line in /etc/default/grub
GRUB_DISABLE_OS_PROBER=false
slow boot
You can check what apps cause a slowing of your boot, in Linux, with this command:
systemd-analyze blame
You should see something like the following
systemd-analyze blame
3.115s NetworkManager-wait-online.service
1.980s fwupd-refresh.service
1.928s fwupd.service
[…]
To disable NetworkManager-wait-online.service, i.g., you can type: sudo systemctl disable NetworkManager-wait-online.service.
other possible causes
Check also if your UUID (of swap partitions, i.g.) are correct. This can be a cause of a severe slowing.
grub rescue
It could happen that your PC, after some operations (i.g. with gdisk) doesn’t start booting and you are therefore in grub rescue prompt. A very unpleasant situation.
The steps to follow are:
- see what are the partitions, with the command
ls- you should see something like:
(hd0)(hd0,msdos1)(hd0,msdos2)(hd1)(hd1,gpt1)
- you should see something like:
- understand what is the right partition to boot (i.g. hd0,gpt2):
- you can list a single partition to see what it contains, with the command ls (hd0,gpt2). You should be able to see if a partition is the right one.
- give the command
set prefix=(hd0,gpt2)/boot/grub - give the command
set root=(hd0,gpt2)/ root=/dev/sda2(if the right partition is hd0,gpt2 the name is /dev/sda2, if it was hd1,gpt3 it would be /dev/sdb3) - give the command
insmod normal - give the command:
normal(orboot)
In this way the system should start with the expected partition.
boot useful tips
- It is not necessary to start booting with EFI if you have GPT partitions (you could choose to have legacy boot with GPT partitions).
- It is not necessary that EFI partition be at the start of a disk: it could be in every place, provided that it has a) boot (esp) flags, and b) at least 110mb of space.
System not starting after upgrading to Ubuntu 22.04
After upgrading Ubuntu from 20.04 to 22.04 it can happen that you cannot start the desktop: emergency mode.
In some case it could be happened that fstab was modified and the efi partition is set with a wrong UUID. Therefore you can try to change, in your fstab file, the efi UUID (i.g. copying it from a working installation).
ssd slow (in Linux)
If your SSD has become slow, it could depend from the swap file: f.e. in fstab the ssd swap UUID could be wrong (after some partitions changes in your SSD).
You can fix this by giving to the swap partition the correct UUID.
a non-destructive way to modify a multi-boot
You can try gdisk: a very simple, easy, fast and safe, command-line tool.
With gdisk you can make several actions, such as:
- convert a MBR disk to a GPT one (with the command gdsk and then the disk you want modify , i.g. /dev/sda, and the doing the command “w”, that is “write”)
- re-order your partition table (with the command “s”, that is “sort”), if in your disk there is some “desorder”, i.g. if /dev/sdb8 is before /dev/sdb6.
Be careful, if you get a warning message that partitions will be deleted: it can really happen.
But mainly be careful that if you change the order of SO partitions you could not be more able to boot.