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The Fedora 15 grub.conf have timeout=0 , so it boots directly to Fedora without showing any grub menu. Is there a way to halt the booting at grub anyway ?
(The issue is an upgraded kernel doesn't boot, and I'd like to just boot the prior kernel version without having to go to a rescue CD and edit grub.conf)
Hold ESC right after boot.
I have dual boot with timeout=0, this is the way how I'm getting access to the menu.
I had the same problem, but just hitting ESC would show me a so called GRUB CLI. It's not a menu but rather a console. I don't think there is a way to change timeout settings from that GRUB CLI, however, there is a way to instruct it to load specific kernel with specific options.
So, the first thing I did is I printed the current grub config.
cat /etc/default/grub
It can print too much, so we need some kind of pagination:
set pager=1
Once we do that, you can find something similar in that output:
menuentry 'Ubuntu, with Linux 4.14.27-041427-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.14.27-041427-generic-advanced-f3f8e7bc-b337-4194-88b8-3a513f6be55b' {
recordfail
savedefault
load_video
gfxmode $linux_gfx_mode
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod ext2
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root f3f8e7bc-b337-4194-88b8-3a513f6be55b
else
search --no-floppy --fs-uuid --set=root f3f8e7bc-b337-4194-88b8-3a513f6be55b
fi
echo 'Loading Linux 4.14.27-041427-generic ...'
linux /boot/vmlinuz-4.14.27-041427-generic root=UUID=f3f8e7bc-b337-4194-88b8-3a513f6be55b ro quiet splash loglevel=0 vga=current udev.log-priority=3 fastboot kaslr acpiphp.disable=1 crashkernel=384M-2G:128M,2G-:256M $vt_handoff
echo 'Loading initial ramdisk ...'
initrd /boot/initrd.img-4.14.27-041427-generic
So, what I did next was I took a photo of everything in that entry, finished pagination until I get back to GRUB CLI.
And started to copy over the commands ignoring 'if' anc 'echo' statements:
recordfail
savedefault
load_video
gfxmode $linux_gfx_mode
insmod gzio
insmod part_gpt
insmod ext2
search --no-floppy --fs-uuid --set=root f3f8e7bc-b337-4194-88b8-3a513f6be55b
linux /boot/vmlinuz-4.14.27-041427-generic root=UUID=f3f8e7bc-b337-4194-88b8-3a513f6be55b ro quiet splash loglevel=0 vga=current udev.log-priority=3 fastboot kaslr acpiphp.disable=1 crashkernel=384M-2G:128M,2G-:256M $vt_handoff
initrd /boot/initrd.img-4.14.27-041427-generic
Note: TAB will help you to choose the right linux and initrd, type /boot/vmlinuz and then TAB, you will be prompted with options. Same for initrd, type /boot/initrd and TAB.
The root uuids are very important, make sure you typed them correctly. Also, since I lost my root password I wanted to start a single user recovery mode in order to set the password, so to the end of the linux xxx I have added recovery single.
The last thing you need to do is to execute in the GRUB CLI:
boot
That will load the linux using the data provided above. In my case I got to recovery and changed the user password using passwd command.
Hope that helps.
See my answer here for how to set things up so that the GRUB boot menu is interruptible when timeout=0.
