# Install grub.  Change /sda to your drive, may need to specify the efi partition.

$ grub-install /dev/sda

# If your boot and partitions are mounted.

$ grub-mkconfig -o /run/media/liveuser/BOOT/grub2/grub.cfg


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# If You have system with several partitions. (Example)

# Get the list of all partions and disks

$ lsblk -o name,mountpoint,label,size,uuid

## NAME   MOUNTPOINT LABEL   SIZE UUID
## sdb                        15G 
## ├─sdb2 /                 13,5G cfaad2ca-1f65-483b-867d-c5a7221da8ac
## ├─sdb3 [SWAP]     SWAP      1G 9afa1f80-fd04-4894-ab89-5a97265f378f
## └─sdb1 /boot              512M 36dbc980-2076-41e1-bfba-bb0404d3746f
## sr0                      1024M 
## sda                     931,5G 
## ├─sda2            TEMP   10,4G 14088554-f243-4d7d-b81c-f3103da615af
## ├─sda7            VAR    15,7G ed42a8ce-47b3-467d-a50c-0193756326ec
## ├─sda5            ROOT   35,2G 2dc70bea-44b0-435b-bc05-9aea8203bd4d
## ├─sda3                      1K 
## ├─sda1            BOOT    512M b6318800-fd89-49ec-bc21-eeafd179dc5f
## ├─sda8            SWAP    4,9G f4c9a05b-7bd3-49b6-9152-4c002833b09e
## └─sda6            HOME  864,9G c72c567b-d8c9-4a65-9e99-d111f554f99a

$ mount /dev/sda5 /mnt
$ mount /dev/sda1 /mnt/boot
$ mount /dev/sda7 /mnt/var
$ mount /dev/sda2 /mnt/tmp
$ for dir in /dev /proc /sys /run; do mount --bind $dir /mnt/$dir ; done

$ grub-install --root-directory=/mnt /dev/sda
$ grub-install --root-directory=/mnt --recheck /dev/sda



# If the grub.cfg should be recreate
$ chroot /mnt

$ ls -la /boot/grub


$ cp /boot/grub/grub.cfg /boot/grub/_grub.old

$ update-grub