see the order of the wanted kernel. Starts from 0.
Example:
... ### BEGIN /etc/grub.d/10_linux ### menuentry 'Ubuntu, with Linux 2.6.35-30-server' --class ubuntu --class gnu-linux # this is 0 --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos1)' search --no-floppy --fs-uuid --set 71119ab7-e93f-49a9-80f1-efc11398c954 linux /boot/vmlinuz-2.6.35-30-server root=UUID=71119ab7-e93f-49a9-80f1 -efc11398c954 ro quiet initrd /boot/initrd.img-2.6.35-30-server } # this is 1 menuentry 'Ubuntu, with Linux 2.6.35-30-server (recovery mode)' --class ubuntu - -class gnu-linux --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos1)' search --no-floppy --fs-uuid --set 71119ab7-e93f-49a9-80f1-efc11398c954 echo 'Loading Linux 2.6.35-30-server ...' linux /boot/vmlinuz-2.6.35-30-server root=UUID=71119ab7-e93f-49a9-80f1 -efc11398c954 ro single echo 'Loading initial ramdisk ...' initrd /boot/initrd.img-2.6.35-30-server } # this is 2 menuentry 'Ubuntu, with Linux 2.6.32-28-server' --class ubuntu --class gnu-linux --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos1)' search --no-floppy --fs-uuid --set 71119ab7-e93f-49a9-80f1-efc11398c954 linux /boot/vmlinuz-2.6.32-28-server root=UUID=71119ab7-e93f-49a9-80f1 -efc11398c954 ro quiet initrd /boot/initrd.img-2.6.32-28-server } # this is 3 menuentry 'Ubuntu, with Linux 2.6.32-28-server (recovery mode)' --class ubuntu - -class gnu-linux --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos1)' search --no-floppy --fs-uuid --set 71119ab7-e93f-49a9-80f1-efc11398c954 echo 'Loading Linux 2.6.32-28-server ...' linux /boot/vmlinuz-2.6.32-28-server root=UUID=71119ab7-e93f-49a9-80f1 -efc11398c954 ro single echo 'Loading initial ramdisk ...' initrd /boot/initrd.img-2.6.32-28-server } ### END /etc/grub.d/10_linux ### ...
2. vi /etc/default/grub
change GRUB_DEFAULT=0 value to wanted kernel
Example:
If we want to boot to 'Ubuntu, with Linux 2.6.32-28-server' we should set 2
3. run update-grub to update
4. reboot and check with uname -r to see if correct kernel selected.