Quick Answer
The answer is boot /kernel. This is the correct command because when a Junos device fails to boot and drops to the loader prompt—typically U-Boot—the bootloader requires the explicit filesystem path to the kernel to initiate the operating system. Issuing boot /kernel tells the loader to locate and execute the kernel file from the default root directory, bypassing any corrupted or missing boot configuration. On the JNCIA-Junos exam, this scenario tests your understanding of the boot sequence and recovery procedures, often appearing as a troubleshooting question where the device cannot load Junos automatically. A common trap is choosing boot without a path or boot /junos, which are invalid at the loader prompt. Remember the memory tip: “Kernel is the core, so boot /kernel to restore.”
This JNCIA-JUNOS practice question tests your understanding of junos os fundamentals. 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.
A Junos device fails to boot and enters the loader prompt. Which command should be used to boot the device into the Junos kernel from the loader prompt?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
load kernel
Why wrong: This is not a loader command.
boot device
Why wrong: Not a valid loader command.
boot
Why wrong: Boot without arguments may try default but not guaranteed to load kernel.
boot /kernel
This command boots the Junos kernel from the loader.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
boot /kernel
When a Junos device fails to boot and drops to the loader prompt (U-Boot or similar), the correct command to manually load the Junos kernel is 'boot /kernel'. This command instructs the bootloader to locate and execute the kernel file from the default filesystem path. Option D is correct because it specifies the full path to the kernel, which is required at the loader prompt to initiate the Junos OS boot process.
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.
load kernel
Why it's wrong here
This is not a loader command.
boot device
Why it's wrong here
Not a valid loader command.
boot
Why it's wrong here
Boot without arguments may try default but not guaranteed to load kernel.
boot /kernel
Why this is correct
This command boots the Junos kernel from the loader.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates familiar with generic bootloaders might assume 'boot' alone is sufficient, but Junos requires the explicit path '/kernel' at the loader prompt to bypass automatic boot attempts and force a manual kernel load.
Trap categories for this question
Command / output trap
This is not a loader command.
Detailed technical explanation
The Junos loader prompt (often U-Boot) operates independently of the Junos kernel and provides low-level commands for system recovery. The 'boot /kernel' command uses the bootloader's filesystem support to read the kernel image from the root of the default partition (typically /kernel). In scenarios where the bootloader cannot find the kernel automatically due to configuration corruption or filesystem errors, specifying the exact path ensures the kernel is loaded, allowing the device to proceed with the boot process and eventually mount the Junos filesystem.
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.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Junos OS Fundamentals — This question tests Junos OS Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: boot /kernel — When a Junos device fails to boot and drops to the loader prompt (U-Boot or similar), the correct command to manually load the Junos kernel is 'boot /kernel'. This command instructs the bootloader to locate and execute the kernel file from the default filesystem path. Option D is correct because it specifies the full path to the kernel, which is required at the loader prompt to initiate the Junos OS boot process.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JNCIA-JUNOS exam.
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