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Some options for installing GRUB to disk, adding a new OS to GRUB, or updating GRUB
(there are other ways, such as writing to a custom and adding using the OS prober)

1 ....Boot a new OS with Super Grub2 on a thumb drive
then enter in the terminal in the booted OS:
sudo apt-get install grub
sudo grub-install /dev/sda
(where "sda" is the root of the hard disk you want to install GRUB on)

super grub2 (boots into a OS with no GRUB yet installed on the machine)

2 ....Add OS to the GRUB menu and set a splash screen with Grub Customizer
this is easy if there is already an OS on the machine with this programme installed - it tends to work fine detecting other Linux installs, but it may fail detecting Win7 or Win8 OS, Android etc.

get from Ubuntu page here and run apt-get install -f if there are needed dependencies

make sure you have installed dependencies
sudo apt-get install cmake libgtkmm-3.0-dev libssl-dev libarchive-dev
(check the list on the site page)

unpack it and build with (note the "dot" after "cmake")
cmake .
sudo make install

  1. On running it searches for OS's. Then you can edit the names to alter how they will appear on the GRUB menu at boot.  
  2. Change any particulars, like the time out for GRUB screen. 
  3. click save and then >File >write to MBR for GRUB to be updated (File >save only saves settings in Grub Customizer).

3 ....Boot Repair Disk
Run this Live CD and the Recovery app automatically searches for OS's.  Open the Advanced options to choose location to install GRUB (set it to the root of your main harddisk, e.g. sda) and any other particulars. 

You can install Boot repair to your system as well, but to detect and repair GRUB it must be run during a live session.

    1. get packages boot-repair and boot-sav .. 
download from or
    2. install glad2script - download and install the .deb package from
sudo dpkg glad<tab>
    3. get and install parted -
    4. then install the boot-sav package with dpkg
    5. finally install boot-repair package with dpkg

4 ....Chroot from a Live environment into the new OS's partiton and install GRUB,
mount /dev/sda2 /mnt
mount -t proc none /mnt/proc
mount -o bind /dev /mnt/dev
mount --bind /sys /mnt/sys
chroot /mnt
grub-install /dev/sda

5 ....Using Rescue Mode of a net install CD
type "rescue" at boot prompt ? or select Advanced > Graphical Rescue Mode
when it arrives at rescue mode, select the mount point for the OS partition e.g. sda5
test the internet connection
edit /etc/apt/sources.list if necessary
apt-get update
apt-get install grub
grub-install /dev/sda

6 ....Using a custom entry
which is really what Grub Customizer (above) does for you - but it might not pick up the OS!  It didn't pick up a Windows 7 OS on a laptop I installed Debian on recently, so I had to use this manual approach.
  1. edit the file /etc/grub.d/40_custom with an entry for the OS to be added (see examples on the Arch Wiki page)
  2. then run: sudo update-grub - OS prober will look for the OS in the custom entries file and add it to GRUB

Read up here

Removing a non-present OS from the GRUB menu
from a booted OS run:
sudo update-grub

Read up on Grub