grub2 background color on Ubuntu

• 17.10 and later:
  

  sudo -H gedit /usr/share/plymouth/themes/default.grub
  

And change the grub background color as you want, in my case I change grub background to black (0,0,0)

if background_color 0,0,0 ; then
   clear
fi

Then, update grub

sudo update-grub


https://askubuntu.com/questions/47488/how-to-change-the-purple-background-color-in-grub

Nice teal that stands out from Win and Ubuntu alike: rgb(0, 123, 96)

Ubuntu upgrade kernel

Install ukuu and run it to get other kernel:
https://linuxhint.com/upgrade-kernel-ubuntu-1804/

Disable secure boot using an older kernel selected at grub level
https://wiki.ubuntu.com/UEFI/SecureBoot/DKMS

Only install critical security updates on ubuntu

I read the apt-get man page carefully when I got tired of manually editing the sources.list every time I wanted to only apply security updates (that means the second time).
Figured this solution out:

sudo cp /etc/apt/sources.list /etc/apt/security.sources.list

Edit the latter to contain only security repositories, then:

sudo apt-get upgrade -o Dir::Etc::SourceList=/etc/apt/security.sources.list

https://serverfault.com/questions/270260/how-do-you-use-apt-get-to-only-install-critical-security-updates-on-ubuntu 

Fix dual boot time discrepancy

http://ubuntuhandbook.org/index.php/2016/05/time-differences-ubuntu-1604-windows-10/

1. Disable UTC and use Local Time in Ubuntu:
In previous Ubuntu editions, you can edit the config file /etc/default/rcS to disable UTC.
In Ubuntu 16.04, open terminal (Ctrl+Alt+T) and run the command below instead:

timedatectl set-local-rtc 1 --adjust-system-clock

To check out if your system uses Local time, just run:

timedatectl