Junos File System: Understanding /config and /var/tmp
Which THREE statements about the Junos OS file system are true? (Choose three.)
⚠ Common exam trap
A common mix-up: candidates confuse the `/etc` directory (which stores system configs, not logs) with the standard Linux convention, or they mistakenly think `/altroot` is for user files instead of its actual purpose as a backup root filesystem.
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
✓
The active configuration is stored in the /config directory
Option C is correct because the active Junos configuration is saved as juniper.conf.gz in the /config directory, which is a separate partition from the root file system. Option D is correct because Junos OS writes its log files, such as messages and interactive-commands, into the /var/log directory. Option E is correct because the Junos OS file system is a FreeBSD-based, UNIX-like hierarchy containing standard directories including /, /var, and /config. Option A is incorrect because /etc holds system configuration files, not log files, which reside in /var/log. Option B is incorrect because /altroot is a backup root partition used for alternate boot images, not for user-uploaded files, which are typically placed in /var/tmp or /var/home.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The /etc directory contains all log files
Why it's wrong here
In Junos, the /etc directory holds system configuration files for daemons and user/group information, such as passwd and fstab. Log files, however, are consolidated under /var/log (e.g., messages, chassisd, authd logs), not /etc. Misidentifying /etc as the log directory confuses the static system configuration store with the dynamic operational logs that Junos rotates and retains for troubleshooting.
- ✗
The /altroot directory is used for user-uploaded files
Why it's wrong here
/altroot is a reserved backup partition used in dual-root designs, allowing a router to boot from an alternative Junos image during upgrades or recovery. It is a copy of the root file system, not a location for user-uploaded files. User-uploaded files belong in /var/home, /var/tmp, or other writable operational directories; /altroot exists solely for high-availability of the OS itself.
- ✓
The active configuration is stored in the /config directory
Why this is correct
The active Junos configuration is stored as the file juniper.conf.gz in the /config directory, which is a separate partition mounted at boot. This location persists across reboots and is distinct from the running configuration held in /var/run, and from the candidate configuration edited with 'configure'. The /config directory also stores rescue configurations, which provide a known-good fallback if the active file becomes corrupted.
- ✓
Log files are typically stored in /var/log
Why this is correct
Log files in Junos are stored under /var/log, following the FreeBSD-derived layout that separates writeable operational data from static system files. Common logs include messages for syslog, chassisd for hardware events, and authd for authentication. Administrators should look here for troubleshooting rather than /etc, since the latter only holds configuration for system services.
- ✓
The file system is UNIX-like with directories such as /, /var, /config
Why this is correct
Junos is built on a FreeBSD kernel, so its file system is UNIX-like, with a root (/) directory and standard subdirectories such as /var, /etc, /dev, and /proc. The addition of /config and /altroot reflects Junos-specific dual-root and configuration storage needs, but overall, path conventions and permission structures match UNIX semantics. This design allows engineers familiar with UNIX to navigate and script against the OS predictably.
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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.