Dual boot¶

ll /etc/grub.d/: GRUB builds its menu using scripts in /etc/grub.d/. The numbers define the order - lower numbers appear first
Change Script File Order so Windows appear before Linux: sudo mv /etc/grub.d/30_os-prober /etc/grub.d/09_os-prober
Update GRUB sudo update-grub: This rebuilds /boot/grub/grub.cfg with the new order
sudo reboot

Set default boot OS¶

open /etc/default/grub
change GRUB_DEFAULT=2 [order starts from zero] and save it
sudo update-grub and reboot

OS selection time¶

open /etc/default/grub
change GRUB_TIMEOUT=10 [value in second] and save it
sudo update-grub and reboot

Repair grub efi overwritten by windows update¶

https://askubuntu.com/questions/88384/how-can-i-repair-grub-how-to-get-ubuntu-back-after-installing-windows

When starting up the computer, it goes straight to Windows, without giving me the option of booting Ubuntu.

Reason: Windows assumes it is the only operating system (OS) on the machine. During update it replaces GRUB with its own boot loader.

Solution: Replace the Windows boot loader with GRUB.

After showing dell logo, press F12
Boot from the live USB, in "Try Ubuntu" mode
Determine the partition number of your main partition sudo fdisk -l
Mount linux partition: sudo mount /dev/nvme0n1p5 /mnt - Linux filesystem
Mount efi partition: sudo mount /dev/nvme0n1p1 /mnt/boot/efi - EFI System
Bind mount some other stuff for i in /sys /proc /run /dev; do sudo mount --rbind "$i" "/mnt$i"; done
sudo chroot /mnt
update grub update-grub
reinstall grub grub-install /dev/nvme0n1
reboot exit and sudo reboot

fsck exited with status code 4¶

The root filesystem on /dev/nvme0n1p5 requires a manual fsck

fsck /dev/nvme0n1p5 -y

After that run exit

Stuck at GRUB command line - GNU GRUB version 2.06-3~deb11u2¶

This means the grub could not find the root system so we need to repair it.

The second answer in the first link is same as the second link

https://askubuntu.com/questions/883992/stuck-at-grub-command-line
https://medium.com/codebrace/rescuing-a-non-booting-grub-on-linux-9409dd623743

find disk and partition info¶

https://ubuntuforums.org/showthread.php?t=2455336

sudo fdisk -lu

My disk is /dev/nvme0n1 and the partition for linux is /dev/nvme0n1p7

find the partition with `/boot/grub`¶

Type ls to list all partitions that GRUB sees
Use ls (hd0,gpt7)/ command to find the partition with /boot/grub
Ensure this is the linux partition: grub> cat (hd0,gpt7)/etc/issue will return Ubuntu 20.04 LTS \n \l

temporally boot from grub into the linux system (only works once)¶

In the second line root=/dev/sdX sets the location of the root filesystem. Mine is /dev/nvme0n1. The third line sets the initrd file, which must be the same version number as the kernel.

grub> set root=(hd0,gpt7)
grub> linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
grub> initrd /boot/initrd.img-3.13.0-29-generic
grub> boot

making permanent repairs¶

Open a terminal in the linux

sudo update-grub
sudo grub-install /dev/nvme0n1p7

Install the grub to the boot sector of your hard drive and not to a partition.

check security boot enabled or not¶

sudo mokutil --sb-state:

SecureBoot enabled
SecureBoot disabled
SecureBoot disabled\nPlatform is in Setup Mode

disable fast startup in windows¶

Issue:

wifi disappeared after boot from windows
reboot ubuntu will bring back wifi
might due to windows fast startup

https://www.windowscentral.com/software-apps/windows-11/how-to-enable-or-disable-fast-startup-on-windows-11

Power Options
Choose what the power button does
Change settings that are currently unavailable
Under the "Shutdown settings" section, check the "Turn off fast startup" option
Save Changes

Wifi setting is missing¶

power off
disconnect power cable
hold the power button for 30 seconds
wifi should be back - but just a temporal solution (usually reboot works)

Dual boot wrong time¶

https://itsfoss.com/wrong-time-dual-boot/

A hardware clock which is also called RTC (real time clock) or CMOS/BIOS clock. By default, Linux assumes that the time stored in the hardware clock is in UTC, while Windows thinks that the time stored on the hardware clock is local time.

Solution 1¶

Setup for Linux system to use the local time for the hardware clock (RTC)

timedatectl set-local-rtc 1 #0 for UTC time standard, 1 for localtime time standard

Solution 2¶

Setup for Windows system to use the UTC for the hardware clock (RTC).

For 64-bit Windows, open regedit then browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation. Create a new QWORD entry called RealTimeIsUniversal, then set its value to 1. Reboot the system. The clock should now be in UTC time.

Reg add HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation /v RealTimeIsUniversal /t REG_QWORD /d 1