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In Ubuntu 12.04 (or above), how do I set the GRUB time and the default OS (that I see at boot time) as I'm dual-booting Windows (7/8) and Ubuntu (12.04 or above)?

• Press Alt + F2, type gksudo gedit /etc/default/grub press Enter and enter your password.


• 
  

  You will see the following contents:

  
  
  

  
  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="quiet splash"
  GRUB_CMDLINE_LINUX=""
  

  
  



• You can change the default from 0 to any number, corresponding to the entry in the Grub bootup menu (first entry is 0, second is 1, etc.)



• You can change the "hidden timeout" (no menu); and also display the countdown (GRUB_HIDDEN_TIMEOUT_QUIET=false)


• You can force the grub menu to show by commenting out the two GRUB_HIDDEN lines with a # at the beginning of the line



• And set the grub menu timeout (default is 10 seconds)




• Make your changes, press Ctrl + S to save and Ctrl + Q to exit



• 
  Important: Open a terminal with Ctrl + Alt + T and type sudo update-grub to apply the changes you just made


• Reboot and you should see your timeout/default entry change

Linked Question:

• How do I set Windows to boot as the default in the boot loader?

If you read the file that you are editing in the example above (/etc/default/grub), you will notice that the very first couple lines instruct you to run update-grub after making changes in order to update the actual file that grub reads to "get its instructions" (/boot/grub/grub.cfg). Note that you must actually run it with the sudocommand first as you need root privileges to actually run the command (which is why the poster above said to type sudo update-grub). This will cause the changes you made to be written to /boot/grub/grub.cfg. The very next couple lines tell you that you can read the full documentation of options in that file (again, /etc/default/grub) by typing info -f grub -n 'Simple configuration'.

That said, set GRUB_TIMEOUT to -1 if you want to set the "grub time" to be indefinite. In other words, it will never automatically boot. You will have to make a selection.

Finally, to answer your question, here are the descriptions of those "grub hidden lines" straight from the above-referenced documentation:

GRUB_HIDDEN_TIMEOUT
 Wait this many seconds for a key to be pressed before displaying
 the menu. If no key is pressed during that time, boot
 immediately. Unset by default.

GRUB_HIDDEN_TIMEOUT_QUIET
 In conjunction with `GRUB_HIDDEN_TIMEOUT', set this to `true' to
 suppress the verbose countdown while waiting for a key to be
 pressed before displaying the menu. Unset by default.

I hope this helps!

You can use an application called Grub Customizer. It is much more easier.

You can install it by:

sudo add-apt-repository ppa:danielrichter2007/grub-customizer
sudo apt-get update
sudo apt-get install grub-customizer

There is an How-To Geek article about it, How to Configure the Linux GRUB 2 Boot Menu the Easy Way. Also, there is a solved thread on the Ubuntu Forums, Change boot order in GRUB 2 that mentions this tool.

Here are some screen shots of this software:

I followed the first answer but it seems to need updating if you are dual booting with Windows 7 Pro and Ubuntu 16.04. Also make sure secure boot is off in the BIOS.

a) First he says use Alt + F2 when I think he wants to use to open a terminal window. In my case it is Ctrl+Alt+T.

b) In the first entry gksudo gedit /etc/default/grub the gksudo command is not installed by default in Ubuntu 16.04. To get around this do the following in Terminal:

sudo -i and press Enter and give your password and then Enter again.

then type:

gedit /etc/default/grub and press Enter.

c) You will now see the grub change menu as illustrated in answer 1. Follow his answer until he gets to Ctrl + S to save the changes. This doesn't work in Ubuntu 16.04 but you should see a save button in the upper right corner of the screen. Click on that.

d) Ctrl + Q to quit.

e) Next type sudo update-grub and Enter

f) Type exit. You need to do this twice.

g) Reboot

I found that on my computer after a few logons the boot process would not show the grub screen at start up and therefore I could not get into Ubuntu as I had set Windows as my default bootup with a 7 second delay in case I wanted to get into Ubuntu.

To correct this problem you need to get into Windows.

1. Click on the start menu and type CMD in the search box.




2. Right click on the CMD line which should be at the top of the screen produced by the right clicking.




3. Click on run as administrator.




4. On the command line type bcdedit /set bootmgr path EFIubuntugrubx64.efi. This entry has the effect of registering the grub menu with the windows boot manager. (Credit to: Grub not showing on startup for Windows 8.1 Ubuntu 13.10 Dual boot)




5. Finally, I rebooted back into windows.

I hope this helps.