This LPIC-2 practice question tests your understanding of linux kernel and system startup. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
During boot, the kernel panics because the root filesystem cannot be mounted. Which kernel parameter should be added at the GRUB prompt to try an alternative root device?
root=/dev/sdb1
The root= parameter explicitly specifies the root device.
init=/bin/sh
Why wrong: init= specifies a different init program, not the root device.
rescue
Why wrong: rescue is not a standard kernel parameter.
single
Why wrong: single boots into single-user mode, but does not change the root device.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
root=/dev/sdb1
The kernel parameter 'root=' specifies the device for the root filesystem. When the default root device fails to mount, adding 'root=/dev/sdb1' at the GRUB prompt overrides the compiled-in root and tells the kernel to attempt mounting from that alternative block device. This is the standard method to redirect the root mount during boot troubleshooting.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
root=/dev/sdb1
Why this is correct
The root= parameter explicitly specifies the root device.
Related concept
Read the scenario before looking for a memorised answer.
init=/bin/sh
Why it's wrong here
init= specifies a different init program, not the root device.
rescue
Why it's wrong here
rescue is not a standard kernel parameter.
single
Why it's wrong here
single boots into single-user mode, but does not change the root device.
Common exam traps
The trap here is that candidates confuse kernel parameters with bootloader commands or init system targets, mistakenly thinking 'rescue' or 'single' can fix a root device failure when they only affect post-mount behavior.
Detailed technical explanation
The kernel parses the 'root=' parameter to set the 'ROOT_DEV' variable, which is used by the VFS layer to locate and mount the root filesystem. Under the hood, the kernel uses the device's major/minor numbers derived from the device name (e.g., /dev/sdb1 maps to 8,17). In real-world scenarios, this parameter is critical when root is on a different disk due to BIOS boot order changes, RAID array reassembly, or when migrating a system to new hardware.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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FAQ
Linux Kernel and System Startup — This question tests Linux Kernel and System Startup — Read the scenario before looking for a memorised answer..
The correct answer is: root=/dev/sdb1 — The kernel parameter 'root=' specifies the device for the root filesystem. When the default root device fails to mount, adding 'root=/dev/sdb1' at the GRUB prompt overrides the compiled-in root and tells the kernel to attempt mounting from that alternative block device. This is the standard method to redirect the root mount during boot troubleshooting.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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