Crucial Exams

CompTIA Linux+ XK0-006 (V8) Practice Question

During an on-call shift you are alerted that a public-facing CentOS 9 server becomes sluggish every evening around 21:00 UTC. CPU consumption is low, but top shows frequent wake-ups by rsyslogd and systemd-journald, and the 5-minute load average is greater than 10. Running journalctl -u sshd --since "5 minutes ago" reveals thousands of repeating lines such as: sshd: Failed password for invalid user admin from 198.51.100.42 port 58234 ssh2 Engineers worldwide must still be able to open interactive SSH sessions. Which single remediation will most quickly reduce the performance impact of these repeated failed log-in attempts while keeping legitimate SSH access available?

  • Add UseDNS no to sshd's configuration and restart the service so reverse DNS lookups are skipped during handshakes.

  • Raise RateLimitBurst= in /etc/systemd/journald.conf to 20000, then restart systemd-journald to accept larger bursts of log entries.

  • Install and enable the default sshd jail in Fail2ban, adjusting maxretry and bantime to block sources after only a few failed attempts.

  • Set LogLevel QUIET in /etc/ssh/sshd_config and reload the SSH daemon to suppress authentication-failure messages.

CompTIA Linux+ XK0-006 (V8)
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