EX200 Operate running systems Practice Question
Exhibit
[root@server ~]# systemctl status sshd
● sshd.service - OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Mon 2025-03-10 14:22:34 EDT; 5min ago
Process: 1234 ExecStart=/usr/sbin/sshd -D $OPTIONS (code=exited, status=255)
Main PID: 1234 (code=exited, status=255)
Status: "Failed to start sshd"
CGroup: /system.slice/sshd.service
└─1234 /usr/sbin/sshd -D
Jan 10 14:22:34 server sshd[1234]: fatal: Cannot bind any address.
Jan 10 14:22:34 server sshd[1234]: fatal: Cannot bind any address.Refer to the exhibit. What is the most likely cause of this failure?
⚠ Common exam trap
Red Hat often tests the distinction between service startup failures caused by port conflicts versus configuration or SELinux issues, and the trap here is that candidates may assume SELinux or a missing config file is the cause when the error message explicitly states 'address already in use'.
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 process is already bound to port 22.
The error message in the exhibit indicates that the sshd service failed to start because port 22 is already in use. This is a classic port conflict, where another process (e.g., another SSH daemon, a web server misconfigured to use port 22, or a leftover process) has bound to the same TCP port. The system log or `ss -tlnp` would show the PID and name of the conflicting process, confirming that port 22 is unavailable for the new sshd instance.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Another process is already bound to port 22.
Why this is correct
The log message 'Cannot bind any address' is what OpenSSH emits when bind(2) returns EADDRINUSE, meaning another process already holds a listening socket on 0.0.0.0:22 or the specific address configured in sshd_config. This can happen after a failed shutdown leaves an old sshd running, or if another daemon (e.g., a second sshd, a proxy) grabbed port 22. Confirm by checking `ss -tlnp` or `sudo lsof -i :22` to identify the PID holding the port.
- ✗
The sshd service is not enabled.
Why it's wrong here
Whether sshd is enabled (`systemctl enable sshd`) only controls whether it is automatically started at boot; it has no bearing on a runtime bind failure. If the service were merely not enabled, starting it manually would still bind successfully as long as port 22 is free, and `systemctl status sshd` would show "inactive (dead)" or "disabled" rather than a socket bind error at startup. The exhibit showing 'enabled' already rules this out.
- ✗
SELinux is blocking the service.
Why it's wrong here
SELinux enforcement causes denial messages such as 'Permission denied' on socket operations or AVC denials logged via `audit2why`; it does not produce EADDRINUSE, and sshd would fail earlier trying to create its privilege separation directory or write its PID file. A bind conflict is a TCP/IP stack-level issue, independent of SELinux policy, so the error text specifically implicates a port conflict rather than a denial.
- ✗
The /etc/ssh/sshd_config file is missing.
Why it's wrong here
If `/etc/ssh/sshd_config` were missing, sshd would abort during configuration parsing with a 'No such file or directory' or 'fatal: bad permissions' style error before even calling socket() and bind(). The bind is attempted only after startup reads its configuration and generates host keys, so reaching the 'Cannot bind any address' stage proves a valid config file was loaded and the failure is at the network binding layer.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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