JN0-106 Junos OS Fundamentals Practice Question
A Juniper device fails to boot and stops at the 'loader>' prompt. What is the most likely cause of this issue?
⚠ Common exam trap
Many candidates confuse a boot loader failure (loader prompt) with a configuration or authentication issue, assuming that any boot problem is due to a corrupted config or password, when in fact the loader prompt specifically indicates a missing or inaccessible kernel.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bad boot device or missing kernel
When a Juniper device stops at the 'loader>' prompt, it indicates that the boot process has failed to locate or load the kernel (juniper-kernel) from the boot device (e.g., internal flash, USB, or hard disk). This is typically caused by a corrupted boot device, missing kernel image, or incorrect boot device selection in the boot loader (UBoot or CFE). The loader prompt is a low-level environment used for recovery, not a sign of configuration or authentication issues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Bad boot device or missing kernel
Why this is correct
The loader prompt (typically 'loader>') is the bootloader's interactive menu, reached when it cannot locate a valid kernel to load. If the boot device is absent, unreadable, or the kernel file is missing/corrupt, the bootloader cannot proceed with the normal boot sequence and instead drops to this prompt for manual intervention. This is the expected symptom when storage or kernel integrity is compromised.
- ✗
Corrupted configuration file
Why it's wrong here
A corrupted configuration file in Junos does not affect the early boot phase, because the bootloader and kernel do not parse configuration data. Corrupt configuration typically triggers errors during the load or commit phase, causing the RE to reject the config, reboot, or fall back to rescue config, but the system still boots far enough to reach the daemon initialization stage. Therefore, it would not stop at the loader prompt.
- ✗
Hardware failure of the power supply
Why it's wrong here
Power supply failure prevents the device from powering on at all, meaning no console output, no loader prompt, and no system activity. The loader prompt is a software state reached after the hardware has successfully powered up and initialized, so a dead power supply would preclude this entirely. This option describes a hardware issue outside the boot sequence itself.
- ✗
Missing root password
Why it's wrong here
A missing root password does not interrupt the boot process; the system still loads the kernel and starts user-space processes, then presents a login prompt. Without a password you may be unable to log in, but you can recover via the root password recovery process, which operates after boot. The loader prompt is not related to authentication credentials.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 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 JN0-106 exam.