x86: How to Modify Boot Behavior by Editing the GRUB Menu at Boot Time

When you modify the GRUB kernel behavior by editing the GRUB menu at boot time, the changes do not persist over a system reboot. Default boot behavior is restored the next time you boot the system.

1. Reboot the system.

   When the boot sequence begins, the GRUB main menu is displayed.

2. Use the arrow keys to select the boot entry to edit, then type e to access the GRUB edit menu.

3. Use the arrow keys to select the kernel or kernel$ line in this menu.

4. Type e to add boot arguments to the line.

5. Type any additional boot arguments that you want to specify.

6. Press Return to save your changes and return to the previous menu.

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   Note –

   Pressing the Escape key returns you to the GRUB main menu without saving your changes.

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7. To boot the system, type b.

   Changes you make take affect when the system is booted.

Example 11–4 x86: Booting a 32-Bit Kernel on a 64-Bit Enabled System

To boot a 32-bit kernel on a 64-bit capable system, add the kernel/unix argument.

grub edit> kernel /platform/i86pc/multiboot kernel/unix

Example 11–5 x86: Redirecting the Serial Console

To redirect the serial console to ttyb, add the -B console=ttyb argument.

grub edit> kernel /platform/i86pc/multiboot -B console=ttyb

Alternatively, you can use input-device/output-device property, as shown in the following example:

grub edit> kernel /platform/i86pc/multiboot -B input-device=ttyb,output-device=ttyb

This example shows how you would override the serial line speed:

grub edit> kernel /platform/i86pc/multiboot -B ttyb-mode="115200,8,n,1,-"

Caution: In the preceding example, the property value contains commas, which is also a property separator. To avoid confusing the property parser, use double quotation marks around the entire property value.