To edit Grub2 during the boot process try the following:
为了在启动时,编辑GRUB2,可以尝试下面的步骤
Immediately after the BIOS splash screen during boot, press and hold the SHIFT button. This will display you grub containing a list of kernels and recovery options 在启动过程中出现 BIOS 启动画面后,立即按住SHIFT按键。 这将显示包含内核和恢复选项列表的grub。