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hardMultiple SelectObjective-mapped

Troubleshooting SSH Connection Failures on Linux

A Linux server is not accepting SSH connections. The administrator wants to troubleshoot the issue. Which THREE actions should be taken?

Quick Answer

The answer is to check the SSH daemon configuration file, firewall rules, and service status. The primary configuration file for the OpenSSH server, /etc/ssh/sshd_config, controls critical settings like the listening port, permitted authentication methods, and whether root login is allowed; a syntax error or a misconfigured directive here will silently prevent connections. On the CompTIA Linux+ XK0-005 exam, this question tests your systematic approach to service troubleshooting, often hiding traps where a candidate jumps to restarting the service without verifying the config file first. When you cannot SSH into a Linux server, always start by checking the sshd_config for errors, then confirm the sshd service is running with systemctl status sshd, and finally inspect firewall rules using iptables -L or ufw status to ensure port 22 is open. Remember the mnemonic “CSF” — Config, Service, Firewall — to lock in the correct order of attack.

⚠ Common exam trap

CompTIA often tests the misconception that reinstalling a package or rebooting is a valid first troubleshooting step, when in reality, checking configuration files, service status, and firewall rules are the precise, targeted actions required.

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

Check /etc/ssh/sshd_config for configuration errors

B is correct because /etc/ssh/sshd_config is the primary configuration file for the OpenSSH server. Syntax errors, incorrect directives (e.g., PermitRootLogin no, Port 22 commented out), or misconfigured authentication settings can prevent SSH from accepting connections. Checking this file is a fundamental step in troubleshooting SSH 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.

  • Reboot the server

    Why it's wrong here

    Last resort; not a troubleshooting step.

  • Check /etc/ssh/sshd_config for configuration errors

    Why this is correct

    Correct: Misconfiguration can prevent connections.

  • Check if sshd service is running (systemctl status sshd)

    Why this is correct

    Correct: First step to ensure service is active.

  • Reinstall the SSH package (apt reinstall openssh-server)

    Why it's wrong here

    Drastic; not a first troubleshooting step.

  • Check firewall rules (iptables -L or ufw status)

    Why this is correct

    Correct: Firewall may be blocking port 22.

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Same concept, more angles

1 more way this is tested on XK0-006

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A user is able to ping the Linux server but cannot connect via SSH. The SSH service is running and listening. Which configuration file should the administrator review FIRST?

medium
  • A./etc/pam.d/login
  • B./etc/ssh/sshd_config
  • C./etc/nsswitch.conf
  • D./etc/hosts.allow

Why B: The SSH service is running and listening, but the user cannot connect. This points to a configuration issue within the SSH daemon itself. The `/etc/ssh/sshd_config` file controls SSH server settings such as allowed authentication methods, port numbers, and user access restrictions (e.g., `AllowUsers`, `DenyUsers`, `PermitRootLogin`). Reviewing this file first is the logical step to identify why connections are being rejected despite the service being active.

JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.