grub2更改默认启动项

grub2 和 grub0.97 的启动项目差别还是比较大的，最近Ubuntu自动更新，把默认启动项目给更改了，导致很多驱动无法成功加载，需要改回去，这里记录下修改过程：

通过sudo vim /boot/grub/grub.cfg打开grub2的默认配置文件

注意：

grub2的一级和二级 menu 的索引都是从 0 开始的
假如第一个启动项（索引为0）不包含子menu，可以通过修改配置set default="0"把默认启动项设为第一个
如果一个启动项包含子menu，可以通过set default="1> 3"的形式来设置默认启动项，其中1是一级menu的索引，2是二级menu的索引

If you have a submenu in your grub.cfg you should use two digits like this:

grub-reboot '1>3'
The first is menu index, and the second is submenu index.

For example, to boot last entry from config like this:

grep menu /boot/grub/grub.cfg

menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
submenu 'Advanced options for Debian GNU/Linux' $menuentry_id_option 'gnulinux-advanced-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 4.6.0-0.bpo.1-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.6.0-0.bpo.1-amd64-advanced-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 4.6.0-0.bpo.1-amd64 (sysvinit)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.6.0-0.bpo.1-amd64-init-sysvinit-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 4.6.0-0.bpo.1-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.6.0-0.bpo.1-amd64-recovery-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 3.16.0-4-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-4-amd64-advanced-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 3.16.0-4-amd64 (sysvinit)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-4-amd64-init-sysvinit-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
    menuentry 'Debian GNU/Linux, with Linux 3.16.0-4-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-4-amd64-recovery-1ffa16a9-fda2-43b5-91b9-c91a08ff190f' {
you should use: