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 with the correct answer and an explanation. Start a timed exam below, or scroll on to read through the questions.
Troubleshooting practice questions
Answers and explanations are shown. Take the timed exam above to test yourself first.
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.
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