Grub: reboot to specific kernel
I’d like to ask for help getting grub-reboot to work. The theory: According to this blog post (and other sources) I should be able to choose the kernel for the next reboot, using grub-reboot . However, this does not work for me; grub always boots to the default kernel. Here’s what I tried:
$ grep GRUB_DEFAULT /etc/default/grub GRUB_DEFAULT=saved $ grep "menuentry " /boot/grub/grub.cfg menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-f3a807d1-3fd6-4970-b741-5382e9801060' < menuentry 'Ubuntu, with Linux 4.4.0-43-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-43-generic-advanced-f3a807d1-3fd6-4970-b741-5382e9801060' < menuentry 'Ubuntu, with Linux 4.4.0-43-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-43-generic-recovery-f3a807d1-3fd6-4970-b741-5382e9801060' < menuentry 'Ubuntu, with Linux 4.4.0-36-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-36-generic-advanced-f3a807d1-3fd6-4970-b741-5382e9801060' < menuentry 'Ubuntu, with Linux 4.4.0-36-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-36-generic-recovery-f3a807d1-3fd6-4970-b741-5382e9801060' < # Version 1, using the name $ sudo grub-reboot "Ubuntu, with Linux 4.4.0-36-generic" # Version 2, using the id $ sudo grub-reboot gnulinux-4.4.0-36-generic-advanced-f3a807d1-3fd6-4970-b741-5382e9801060 # Version 3, counting $ sudo grub-reboot 3 Neither of these commands seem to have an effect; after reboot, I always end up with the 4.4.0-43 kernel. Note: This is on Ubuntu 16.04 Xenial. It is a server machine and I don't have access to the console during boot, so I can't look at the grub menu 🙁
Mark: Sorry, I have SSH access but no physical access. Trying to get an IPMI console to work now. that might help.
Patrick: I'm running into a bug with a newer version of the Kernel. The previous one worked. Also, AFAIK I can't apt-get purge the one kernel that's currently running.
4 Answers 4
Display Grub Menu Entries from Command Line
I created a script grub-menu.sh to make it easy to find the menu entry number:
Booting with Grub Menu Entry Number
If you wanted to reboot into Kernel 4.4.0-131 you would use:
Getting the bash script grub-menu.sh
It seems the kernel you want to boot is in a submenu of grub (just look at the complete grub.cfg ). man grub-reboot says:
Please note that menu items in submenus or sub-submenus require specifying the submenu components and then the menu item component. The titles should be separated using the greater-than character ( > ) with no extra spaces. Depending on your shell some characters including > may need escaping. More information about this is available in the GRUB Manual in the section about the 'default' command.
Maybe something like grub-reboot '2>2' will work for you.
I've been in a similar situation, and wanted a simple way to reboot into a different kernel or set the default. The menus that are generated in Ubuntu do make this less than trivial.
I've put together a script called boot-kernel that makes this easier. Its not perfect, but works well for at least official ubuntu kernels.
$ sudo ./boot-kernel --setup-only changing GRUB_DEFAULT from 0 to "saved" in /etc/default/grub apply change to /etc/default/grub --- /etc/default/grub 2018-01-12 19:40:38.681080878 +0000 +++ /tmp/boot-kernel.GXbsRC 2018-01-12 19:40:50.525044373 +0000 @@ -3,7 +3,7 @@ # For full documentation of the options in this file, see: # info -f grub -n 'Simple configuration' -GRUB_DEFAULT=0 +GRUB_DEFAULT=saved GRUB_HIDDEN_TIMEOUT=0 GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=0 execute: update-grub Generating grub configuration file . Found linux image: /boot/vmlinuz-4.4.0-109-generic Found initrd image: /boot/initrd.img-4.4.0-109-generic Found linux image: /boot/vmlinuz-4.4.0-108-generic Found initrd image: /boot/initrd.img-4.4.0-108-generic done $ sudo ./boot-kernel /boot/vmlinuz-4.4.0-108-generic GRUB_DEFAULT already set to 'saved'. no change necessary. selected /boot/vmlinuz-4.4.0-108-generic. entry: Advanced options for Ubuntu>Ubuntu, with Linux 4.4.0-108-generic execute: grub-reboot "Advanced options for Ubuntu>Ubuntu, with Linux 4.4.0-108-generic"