JN0-106 Junos OS Fundamentals Practice Test 4 — 15 Questions

Question 1

Which Junos CLI mode allows a user to view the configuration and execute operational commands, but not make configuration changes?

Accepted Answer

Operational mode. In Junos OS, Operational mode (indicated by the `>` prompt) allows users to execute operational commands (e.g., `show`, `ping`, `traceroute`) and view the active configuration using `show configuration`, but it does not permit any changes to the configuration. Configuration changes require entering Configuration mode (indicated by the `#` prompt) via the `configure` command. This separation enforces a strict two-tier access model, ensuring that operational tasks do not inadvertently alter the device's configuration.

Answer

Monitor mode

Answer

Enable mode

Answer

Configuration mode

Question 2

A network administrator makes several changes to the configuration but decides to discard all uncommitted changes and start fresh. Which command should be used to revert the candidate configuration back to the current active configuration?

Accepted Answer

rollback 0. The 'rollback 0' command reverts the candidate configuration to the currently active configuration, discarding all uncommitted changes. This is because Junos maintains a rollback database of the last 50 committed configurations, with index 0 always representing the active configuration. Using 'rollback 0' effectively resets the candidate configuration to match the active one, allowing the administrator to start fresh without affecting the running system.

Answer

load override

Answer

commit check

Answer

rollback 1

Question 3

A Juniper device fails to boot and stops at the 'loader>' prompt. What is the most likely cause of this issue?

Accepted Answer

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

Corrupted configuration file

Answer

Hardware failure of the power supply

Answer

Missing root password

Question 4

A technician notices that the /var partition on a Junos device is 95% full. Which action will immediately free up disk space without affecting device operation?

Accepted Answer

Clear log files using 'clear log messages'. The 'clear log messages' command immediately removes the contents of the active log files (e.g., messages, interactive-commands) without requiring a reboot or affecting running processes. This directly frees up space in /var/log, which is a primary consumer of the /var partition, while leaving the directory structure intact so logging continues normally.

Answer

Delete unused software packages using 'request system software delete'

Answer

Reboot the device

Answer

Remove the /var/log directory

Question 5

Which command is used to view the terminal history of commands entered by the user?

Accepted Answer

show cli history. The 'show cli history' command displays the list of previously entered CLI commands in the current session, allowing users to recall and re-execute them. This is a Junos-specific command that provides a terminal history feature, distinct from the commit history or system logs.

Answer

show system commit

Answer

show configuration

Answer

show log messages

Question 6

A network operator needs to backup the current configuration to a file on the local flash. Which command accomplishes this?

Accepted Answer

show configuration | save /var/tmp/backup.conf. The correct command to backup the current configuration from operational mode is `show configuration | save /var/tmp/backup.conf`. This pipes the active configuration to the save command, writing it to the specified file. Option B (`save /var/tmp/backup.conf`) is a configuration mode command and will not work in operational mode. Option A saves the rescue configuration, not the active configuration. Option C commits the configuration and exits but does not save to a file.

Answer

request system configuration rescue save

Answer

save /var/tmp/backup.conf

Answer

commit and-quit

Question 7

An engineer suspects that a recent software upgrade caused a compatibility issue. Which command should be used to revert the Junos OS to the previous version?

Accepted Answer

request system software rollback. The 'request system software rollback' command is the correct method to revert the Junos OS to the previously installed version. This command triggers a reboot and loads the previous software set from the /altroot partition, effectively undoing the upgrade while preserving the configuration.

Answer

rollback 0

Answer

request system reboot

Answer

request system software delete jinstall-*.tgz

Question 8

Refer to the exhibit. Which filesystem should the administrator investigate to free up disk space?

Accepted Answer

/var. The /var filesystem on Junos devices stores system logs, core dumps, and temporary files. When disk space is low, /var is the most common culprit because it contains rotating log files (e.g., messages, interactive-commands) and crash data that can accumulate rapidly. The administrator should investigate /var to free up space by clearing old logs or core files.

Answer

/config

Answer

/ (root)

Answer

/dev

Question 9

Refer to the exhibit. Which log file will contain messages about authorization events?

Accepted Answer

messages. In Junos, the 'messages' log file (typically /var/log/messages) records system log messages, including authorization events such as user login failures, privilege escalation attempts, and configuration changes. Authorization events are generated by the system's authentication, authorization, and accounting (AAA) framework and are logged at the 'info' severity level by default, which is captured in the messages file. The 'interactive-commands' log file specifically records CLI commands entered by users, not authorization events.

Answer

Both messages and interactive-commands

Answer

Neither

Answer

interactive-commands

Question 10

Which THREE actions can be performed in operational mode on a Junos device?

Accepted Answer

Ping a remote host. In Junos, operational mode is the CLI mode entered after login (prompt user@host>), used for monitoring and controlling device state. Option B (Ping a remote host) is correct because the ping command is an operational-mode command used to test reachability to a remote host. Option D (View system logs) is correct because operational mode provides commands such as show log messages to inspect system log files. Option E (Reboot the chassis) is correct because the request system reboot command is executed from operational mode to restart the device. Options A and C are not operational-mode actions: committing configuration changes (commit) and configuring interface IP addresses (set interfaces ...) are performed in configuration mode, which is entered with the configure command.

Answer

Commit configuration changes

Answer

Configure interface IP addresses

Question 11

Which TWO commands are used to install and remove software packages on a Junos device?

Accepted Answer

request system software delete. Option A, `request system software delete`, is correct because it is the Junos operational-mode command used to remove an installed software package (such as a Junos image or an individual package) from the device. Option E, `request system software add`, is correct because it is the Junos command used to install a new software package or Junos image onto the device, typically referencing a local file or URL. Option B, `request system software rollback`, is incorrect because it reverts the system to a previously installed software version rather than installing or removing a package. Option C, `show system software`, is incorrect because it only displays information about installed software and does not modify it. Option D, `request system reboot`, is incorrect because it restarts the device and does not install or remove any software package.

Answer

request system software rollback

Answer

show system software

Answer

request system reboot

Question 12

Which command shows the operational status of all interfaces in a brief format?

Accepted Answer

show interfaces terse. The 'show interfaces terse' command displays a brief, one-line summary of each interface, including its administrative status (up/down), link status, protocol status, and configured IP addresses. This is the correct command for a concise overview of all interfaces' operational state, as specified in the Junos OS documentation.

Answer

show interfaces statistics

Answer

show interfaces detail

Answer

show configuration interfaces

Question 13

What is the default behavior when a user logs in to a Junos device and enters configuration mode?

Accepted Answer

The user can edit the candidate configuration.. When a user enters configuration mode on a Junos device, they are placed into a private copy of the candidate configuration. This allows the user to make changes without affecting the active configuration until a commit operation is performed. Option B correctly describes this default behavior.

Answer

The user must first commit before making changes.

Answer

The user can only view the configuration.

Answer

The user directly modifies the active configuration.

Question 14

Refer to the exhibit. The network administrator made a change that caused connectivity loss. They need to revert to the configuration before the most recent commit. Which command would accomplish this?

Accepted Answer

rollback 1. In Junos, rollback numbers are stored with 0 being the most recent committed configuration. To revert to the configuration before the most recent commit, you need to load the configuration that was active before that change. That is rollback 1, which represents the second most recent commit. Using rollback 0 would load the configuration that caused the issue, not fix it.

Answer

rollback 0

Answer

rollback 3

Answer

rollback 2

Question 15

An engineer needs to copy a configuration from one device to another. Which command should be used to export the current active configuration in a mergeable format?

Accepted Answer

show configuration | display set. The 'show configuration | display set' command outputs the current active configuration as a series of 'set' commands, which can be directly copied and applied to another Junos device using 'load set terminal' or 'load merge'. This format is specifically designed for merging configurations, as it represents the configuration in a flat, non-hierarchical structure that Junos can parse incrementally.

Answer

show configuration | display inheritance

Answer

show configuration | display json

Answer

show configuration | save /var/tmp/config.txt