automatic grub2 choice on remote reboot

[ricoPan]

I'm trying to figure out if I can do a remote reboot (eg over ssh) and specify a new grub2 os choice for the next boot only (once), in order to boot windows remotely once, but then back to linux on the next reboot.

I found this related post for grub, but won't work for grub2 ( I never tried it with grub for a remote reboot).

http://sidvind.com/wiki/GRUB:_Boot_another_OS_once

which suggests changing the default menu option with the once flag:

[root@localhost ~]# echo "savedefault --default=2 --once" | grub --batch
[root@localhost ~]# reboot

I'm just starting to work with grub2 and am not at all clear whether I can do anything similar.

BTW Ubuntu karmic and windows 7.

thanks.

[tobias81]

I'm looking basically for exactly the same thing ...

In my case I have a remote machine that I re-instelled using deb-bootstrap and I wanna try to boot into it just once and if something goes wrong reboot back into the old system... (obviously if something DOES go wrong I can't reconfigure anything)

does anybody have a good idea on how to do this

PS: there is absolutely no way that I can get phisical access to this machine ;/

[chngtrn]

Here are the steps you need to do to achieve what you wanted.

1. Modify /etc/default/grub like below
GRUB_DEFAULT=saved
2. Re-generate /boot/grub/grub.cfg as root
grub-mkconfig > /boot/grub/grub.cfg
3. Set your default OS to boot everytime, replace 0 with 1 for second OS, etc.
sudo grub-set-default 0
4. Set a different OS to boot into once only, replace 1 with 2 if you want to boot 3rd OS, etc.
sudo grub-reboot 1
5. (Optional) Change the entry below in /boot/grub/grub.cfg so that GRUB doesn't stay at the boot screen waiting for input after an abnormal shutdown.
From:
if [ ${recordfail} = 1 ]; then
set timeout=-1
else
set timeout=10
fi

To:
if [ ${recordfail} = 1 ]; then
set timeout=1
else
set timeout=1
fi

[al3azef]

Here's the simple and complete answer:

Important note: Configuration changes are normally made to /etc/default/grub and to the custom files located in /etc/grub.d. The /boot/grub/grub.cfg file should not be edited by the user; changes to this file are made by configuration scripts. After editing /etc/default/grub, you need to run sudo update-grub for your changes to take effect on the next boot.
Some of the most common changes, such as the default OS/kernel and menu timeout, can be changed from within a GUI app called StartUp-Manager. See the community doc StartUpManager for information about how to install and use this application.

/etc/default/grub (file)

• The main configuration file for changing default settings. Upon installation, the following lines are available for alteration by the user:
• GRUB_BACKGROUND - Sets the background image, enter the full path to the image here. See splash image configuration above for further details.
• GRUB_DEFAULT - Sets the default menu entry. Entries may be numeric, a complete menuentry quotation, or "saved"
  
  
  • GRUB_DEFAULT=0 Sets the default menu entry by menu position. As in GRUB, the first "menuentry" in grub.cfg is 0, the second is 1, etc.
  • GRUB_DEFAULT="xxxx" An exact menu entry, including the quotation symbols, may also be used. In this case, location in the menu will not matter. Example: GRUB_DEFAULT="Ubuntu, Linux 2.6.31-9-generic"
  • GRUB_DEFAULT=saved
    
    
    • The information in this section applies to GRUB 1.98 and later.
    • Enables the "grub-reboot" and "grub-set-default" commands to set the default OS.
    • The default OS will not be set by an interactive selection of an OS from the menu.
    • grub-set-default Sets the default boot entry until changed.
      
      
      • The format is sudo grub-set-default X, with X being the menu entry position (starting with 0 as the first entry) or the exact menu string. Examples: sudo grub-set-default 3 or sudo grub-set-default "Ubuntu, Linux 2.6.32-15-generic"
      • To obtain the existing menu entry choice number (starting from 0) or the menu entry "string", run grep menuentry /boot/grub/grub.cfg
    • grub-reboot This command sets the default boot entry for the next boot only. The format of the command is the same as for grub-set-default (see above).

for the complete Guide refer to https://help.ubuntu.com/community/Grub2 Section "Configuration GRUB2"

[TimmGood]

Thanks for the info - exactly what I was looking for. But, on the case exposed with a dual linux/Windows OS (and grub2 as boot loader), is there any way when I've booted on Windows to reboot next time on linux? Should I try to map the ext4 partition in Windows and manually modify the config files (since obviously update-grub or grub-mkconfig cannot be used there)? Any idea? Regards Timm