How can I undo the effects of grub-reboot?

Solution 1:

Use the grub-set-default command.
For example, assuming you want the first grub entry to be your default:

sudo grub-set-default 0

Solution 2:

Open Terminal and type:

cd /etc/default/

Backup your file:

sudo cp grub grub.backup

Edit your file:

gksudo gedit grub

Add this line before the GRUB_DEFAULT=? line:

GRUB_SAVEDEFAULT=true

and change this line to:

GRUB_DEFAULT=saved

Save, close and then run this:

sudo update-grub

Next time, whenever you choose an OS from your grub menu it will be the default one until you choose another one, and so on.

Your first lines will look like these:

GRUB_SAVEDEFAULT=true
GRUB_DEFAULT=saved
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=6
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_CMDLINE_LINUX=""
# ...

Solution 3:

It is working , ...anyway.

the first choice in the grub2 menu is '0' the second one is '1' and so on.......

so your file looks like:

GRUB_DEFAULT=0
#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=""
GRUB_CMDLINE_LINUX=""

................. ......................