grub single boot and kernel panic reboot

So, over the past while i have been working on getting a new kernel working on my system. The problem i was having is that the newer kernels i use are not loading the sata modules properly from the initrd images.

When trying to fix this i would run into the scnenario whereas, i reboot using the new kernel and if it kernel panics, i then have to file a ticket with my hosting provider to reboot the system and select the old kernel.

I have now found 2 ways around this that might be useful for anyone who does a lot of kernel testing.

1.) Booting once-only - (same as lilo -R)

In reference to http://www.gnu.org/s...g-once_002donly

in grub.conf, add the following line to the beginning.

default saved

If for example your grub.conf looks like the one i have below. This boots into the 2.6.20-1.2944 by default.

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Fedora Core (2.6.20-1.2944.fc6)
        root (hd0,0)
        kernel /vmlinuz-2.6.20-1.2944.fc6 ro root=LABEL=/ acpi=off 
        initrd /initrd-2.6.20-1.2944.fc6.img
title Fedora Core (2.6.20-FluKex.com)
        root (hd0,0)
        kernel /vmlinuz-2.6.20-FluKex.com ro root=LABEL=/ acpi=off 
        initrd /initrd-2.6.20-FluKex.com.img

If you want to have it so that 2.6.20-FluKex.com boots on next boot, run the following command from the console before rebooting.
echo "savedefault --default=1 --once" | grub --batch
then
reboot

Now, if you have a kernel that panics and need it to reboot if it panics. change your config and add the panic=# (# being seconds before auto reboot) to the kernel line. Example file below

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Fedora Core (2.6.20-1.2944.fc6)
        root (hd0,0)
        kernel /vmlinuz-2.6.20-1.2944.fc6 ro root=LABEL=/ acpi=off panic=5
        initrd /initrd-2.6.20-1.2944.fc6.img
title Fedora Core (2.6.20-FluKex.com)
        root (hd0,0)
        kernel /vmlinuz-2.6.20-FluKex.com ro root=LABEL=/ acpi=off panic=5
        initrd /initrd-2.6.20-FluKex.com.img

so the order of operations on this are as follows.

1.) Add new kernel to grub.conf
2.) set default=# in grub.conf to the failsafe kernel (the one you want it to try if the other fails)
3.) run the following:
echo "savedefault --default=1 --once" | grub --batch
4.) reboot

This will try the flukex.com kernel, and if it panics, it will reboot and use the normal default kernel.

BLAM works for me.

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