How can I tell GRUB I want to reboot into Windows—before I reboot?

1. Edit the /etc/default/grub and replace GRUB_DEFAULT=0 with GRUB_DEFAULT=saved
2. sudo update-grub

3. Your command will be:

   sudo grub-reboot "$(grep -i windows /boot/grub/grub.cfg|cut -d"'" -f2)" && sudo reboot
   

   A pretty function for your ~/.bashrc or .bash_aliases could look like:

   # Reboot directly to Windows
   # Inspired by http://askubuntu.com/questions/18170/how-to-reboot-into-windows-from-ubuntu
   reboot_to_windows ()
   {
       windows_title=$(grep -i windows /boot/grub/grub.cfg | cut -d "'" -f 2)
       sudo grub-reboot "$windows_title" && sudo reboot
   }
   alias reboot-to-windows='reboot_to_windows'
   

   Editor's notes:

   • I have replaced deprecated backticks (``) by $(...) construct.

   • In general, I have re-written it to adhere to current POSIX (wiki) standards, and while at it, did a few minor other changes.

   • For completeness, I left the below function untouched for comparison.

---

In case, your grub.conf contains multiple lines for Windows, following functions will take care only about lines starting by menuentry and picking just the first one, referring to Windows:

function my_reboot_to_windows {
    WINDOWS_TITLE=`grep -i "^menuentry 'Windows" /boot/grub/grub.cfg|head -n 1|cut -d"'" -f2`
    sudo grub-reboot "$WINDOWS_TITLE"
    sudo reboot
}

In order for the grub-reboot command to work, several required configuration changes must be in place:

• The default entry for grub must be set to saved. One possible location for this is the GRUB_DEFAULT= line in /etc/default/grub
• Use grub-set-default to set your default entry to the one you normally use.
• Update your grub config (e.g. update-grub).

This should take care of the initial set-up. In the future, just do grub-reboot <entry> for a one-time boot of <entry>.

Agree with @jw013. And you can also give the menu tile to grub-reboot (including the title of parent menu). e.g:

$ sudo grub-reboot "Advanced options for Ubuntu>Ubuntu, with Linux 4.13.0-26-generic"
$ sudo reboot

Where "Advanced options for Ubuntu" is the parent menu, "Ubuntu, with Linux 4.13.0-26-generic" is submenu.