LPIC-1 Essential System Services and Networking Practice Question
Exhibit
Refer to the exhibit. # systemctl status sshd ● sshd.service - OpenSSH server daemon Loaded: loaded (/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: failed (Result: start-limit-hit) since Mon 2023-09-18 10:30:45 UTC; 2min ago Process: 1297 ExecStart=/usr/sbin/sshd -D $SSHD_OPTS (code=exited, status=0/SUCCESS) Main PID: 1297 (code=exited, status=0/SUCCESS) Status: "Failed to start SSH daemon: Address already in use"
Based on the exhibit, what is the most likely cause of the SSH service failure?
⚠ Common exam trap
Many exam-takers assume SSH failures are always due to firewall rules or disabled services, but the specific error message 'address already in use' directly points to a port conflict, not a firewall or configuration syntax issue.
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
✓
Another service is already listening on port 22.
The exhibit shows that the sshd service failed to start because the address (0.0.0.0:22) is already in use. This indicates that another process is already bound to port 22, preventing sshd from binding to it. Therefore, the most likely cause is that another service is already listening on port 22.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The sshd service is disabled.
Why it's wrong here
A disabled sshd service would mean no process is listening, but the exhibit shows the daemon attempting to start and failing, which a disabled unit would not produce. Checking unit enablement is right when systemctl status shows inactive and no startup attempt occurs.
- ✗
The firewall is blocking port 22.
Why it's wrong here
A firewall blocking port 22 would prevent connection attempts entirely, yet the exhibit shows sshd failing to start rather than a refused connection. Firewall diagnosis is the right path when the daemon runs but clients cannot reach it, which is not what the evidence here indicates.
- ✓
Another service is already listening on port 22.
Why this is correct
SSH binds to TCP port 22; if another process already holds that port, sshd cannot bind and fails to start. The exhibit's bind error confirms this conflict, making a competing listener the most likely cause rather than configuration or key issues.
- ✗
The SSH configuration file has a syntax error.
Why it's wrong here
A syntax error in sshd_config would cause sshd to reject the file and exit, which is plausible, but the exhibit's specific error output points elsewhere. Syntax checking is the correct avenue when sshd -t reports a parse failure, not when the service is simply not running.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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