Which grub boot option is used to drop into an initramfs debug shell during recovery?

• A. rd.break on the linux16 line
• B. boot=single
• C. init=/bin/sh
• D. rd.break in initramfs

Answer: (A)

Dropping into an initramfs debug shell is achieved by telling the boot process to pause at the early initramfs stage and provide you with a shell for debugging. The grub option to do this is rd.break, placed on the linux16 line of the GRUB menu entry. When the kernel starts with this parameter, dracut stops early in initramfs and presents a debug shell you can use to inspect devices, mount the real root, or fix boot problems before continuing boot. After you’ve made whatever changes you need, you can resume boot and let it proceed.

Other options won’t reliably give you that early initramfs debugging shell: boot=single targets later single-user mode rather than the early initramfs stage; init=/bin/sh runs a shell as the real init and may fail if the root isn’t ready yet, rather than giving you the initramfs debugging environment; and rd.break in initramfs isn’t the standard way to trigger the early break at the grub level.