Configuring the Grub2 boot loader

I had to use Linux for work the last few days, and my previous installation was completely outdated so I reinstalled from scratch, switching distribution in the process (from OpenSUSE to Kubuntu).
Part of the fun in installing Linux on a computer where I still want to mainly use Windows is configuring the bootloader. Apparently, it’s 2017 yet it still has to be done 100% via manually editing configuration files.

The file you want to edit is /etc/default/grub, so:

sudo nano /etc/default/grub

Then the interesting things to change are among those lines:
GRUB_DEFAULT=4 : boot the 5th item in the list (numbering starts at 0, so 5th item is 4, not 5)
GRUB_DEFAULT="Windows 7 (loader)" : boot the item named “Windows 7 (loader)”. NB: for me, for some reason it didn’t work
GRUB_DEFAULT=saved : boot the last operating system you chose (requires to also set GRUB_SAVEDEFAULT=true). NB: for me, the saving failed for some reason so it always loaded the first item :/
GRUB_CMDLINE_LINUX_DEFAULT="" : show console log output when starting up, instead of the static splashscreen (which is the default "quiet splash") (link https://askubuntu.com/questions/477821/how-can-i-permanently-remove-the-boot-option-quiet-splash)

After you’ve saved your modifications, you have to run sudo update-grub to apply them, as /etc/default/grub isn’t directly used by Grub but it used to automatically generate Grub’s configuration files (which is /boot/grub/grub.cfg and shouldn’t be manually modified)

More details there: https://www.howtogeek.com/196655/how-to-configure-the-grub2-boot-loaders-settings/

Bonus 1 my /etc/default/grub file

#GRUB_DEFAULT="Windows 7 (on /dev/sdb1)"
GRUB_DEFAULT=4
#GRUB_DEFAULT=saved
#GRUB_SAVEDEFAULT=true
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_CMDLINE_LINUX=""

Bonus 2: if you happen to have damaged RAM, you can use Grub to enable BadRAM filtering. Not sure how this works exactly, but the setting is called GRUB_BADRAM

Bonus 3: since you’re here, I assume you’re dual booting. Maybe you’re having an issue with Windows and Linux both messing up your system date. Long story short, run "timedatectl set-local-rtc 1" to make Linux store local time instead of UTC in the hardware clock (well at least that’s how it is for Ubuntu). More details: https://help.ubuntu.com/community/UbuntuTime#Multiple_Boot_Systems_Time_Conflicts