Q1. What command shows kernel ring buffer messages?
- A.dmesg✓ Correct
- B.journalctl
- C.syslog
- D.kernlog
Explanation: dmesg displays boot-time and kernel-related messages. Learn more.
CompTIA Linux+ Practice Questions: Troubleshooting
17 free, exam-style CompTIA Linux+ (XK0-006) practice questions covering Troubleshooting. Each question shows the correct answer and a clear explanation. Ready for the real thing? Take the full timed quiz below.
Q2. What does 'journalctl -u nginx' display?
- A.All system logs
- B.Kernel messages
- C.NGINX service logs✓ Correct
- D.User login history
Explanation: -u filters logs by systemd unit (service). Learn more.
Q3. What does 'strace -p <PID>' do?
- A.Trace system calls✓ Correct
- B.Show process tree
- C.Monitor network traffic
- D.Profile CPU usage
Explanation: strace intercepts system calls made by a process. Learn more.
Q4. What does 'logger' command do?
- A.Analyze logs
- B.Write to syslog✓ Correct
- C.Rotate logs
- D.Encrypt logs
Explanation: logger adds entries to the system log. Learn more.
Q5. Which directory contains logrotate configurations?
- A./etc/logrotate.d/✓ Correct
- B./var/log/
- C./usr/lib/logrotate/
- D./etc/rsyslog.d/
Explanation: Custom logrotate configs go in /etc/logrotate.d/. Learn more.
Q6. Which directory contains kernel panic crash dumps?
- A./var/crash✓ Correct
- B./proc/kcore
- C./var/log/kernel
- D./sys/kernel/debug
Explanation: Kernel crash dumps stored in /var/crash by default. Learn more.
Q7. Which command shows open files by process?
- A.lsof✓ Correct
- B.fuser
- C.ps aux
- D.netstat
Explanation: lsof lists open files and their processes. Learn more.
Q8. Which directory contains systemd journal logs?
- A./var/log/journal✓ Correct
- B./run/log
- C./etc/systemd/journal
- D./tmp/journal
Explanation: Persistent journals stored in /var/log/journal/. Learn more.
Q9. What is the purpose of 'systemd-analyze blame'?
- A.List failed services
- B.Show slowest-starting units✓ Correct
- C.Check disk I/O stats
- D.Analyze security vulnerabilities
Explanation: Identifies services impacting boot performance. Learn more.
Q10. What is the purpose of 'logrotate --force'?
- A.Bypass log rotation schedules✓ Correct
- B.Delete old logs
- C.Create new log files
- D.Encrypt rotated logs
Explanation: Forces rotation even if not scheduled. Learn more.
Q11. Which command shows kernel ring buffer messages?
- A.dmesg
- B.journalctl -k
- C.cat /proc/kmsg
- D.All of the above✓ Correct
Explanation: All access kernel messages through different interfaces. Learn more.
Q12. What is the purpose of 'strace -c'?
- A.Count system calls✓ Correct
- B.Continue after signals
- C.Capture network traffic
- D.Colorize output
Explanation: Summarizes system call statistics. Learn more.
Q13. Which command displays the last lines of a log file and can follow new entries?
- A.tail -f✓ Correct
- B.head -n 1
- C.chmod +x
- D.mkfs.ext4
Explanation: tail -f shows the end of a file and continues displaying new lines as they are written. Learn more.
Q14. Which command displays kernel messages from the boot and runtime ring buffer?
- A.dmesg✓ Correct
- B.uname -m only
- C.whoami
- D.groups
Explanation: dmesg prints messages from the kernel ring buffer, useful for hardware and driver troubleshooting. Learn more.
Q15. Which command displays logs for a specific systemd unit?
- A.journalctl -u service✓ Correct
- B.systemctl reload-daemon only
- C.ls -u service
- D.grep -u service
Explanation: journalctl -u filters logs for a named systemd unit. Learn more.
Q16. Which command follows the end of the system journal in real time?
- A.journalctl -f✓ Correct
- B.dmesg -C
- C.last -f
- D.find -journal
Explanation: journalctl -f follows new journal entries as they arrive. Learn more.
Q17. Which command shows messages for sshd from the current boot?
- A.journalctl -u sshd -b✓ Correct
- B.dmesg -u sshd
- C.lastlog -b sshd
- D.systemctl cat sshd --logs
Explanation: journalctl -u filters by the sshd unit, and -b restricts output to the current boot. Learn more.