I'd like to access a grub prompt while booting an Ubuntu 12.04 ISO with Virtualbox.

When keeping the left Shift key pressed while booting, or when pressing Esc, I get stuck in some weird prompt named boot:

Here are some commands I tried:

boot: ls
Could not find kernel image: ls

boot: help
Could not find kernel image: help

boot: .
Invalid or corrupt kernel image.

When pressing Enter (empty command) the system boots.

What is this prompt? What commands does it accept? How can I gain a grub prompt from this?


This is the syslinux prompt.

If the Shift or Alt keys are held down during boot, or the Caps or Scroll locks are set, syslinux will display a lilo(8) -style "boot:" prompt.

You can't access grub from this, but you can press Tab to see what options are accepted.

boot: <press Tab>

boot: live
<system booting>

The prompt also accepts kernel command line arguments:

boot: live quiet splash

Note that his prompt may be very old but there is no way to check its version.

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