Quick Answer
The answer is the pam_securetty.so module, as it restricts root login to terminals listed in /etc/securetty. When this module is misconfigured or set to 'required' for all users, local console and graphical display manager logins—which use virtual terminals like tty1—are blocked, while SSH sessions succeed because they use pseudo-terminals like pts/0 that pam_securetty typically ignores. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of PAM module ordering and terminal types; a common trap is assuming all login methods are affected equally. Remember that pam_securetty only applies to local TTYs, not remote pseudo-terminals. Memory tip: "Secure TTY, not PTY"—if SSH works but local root login fails, check /etc/securetty and the pam_securetty line in /etc/pam.d/system-auth.
This XK0-005 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Linux administrator is troubleshooting login issues. Users can log in using SSH but not through the local console or graphical display manager. The /etc/pam.d/system-auth file was recently modified. Which PAM module is likely misconfigured?
pam_limits.so
Why wrong: Sets limits but does not prevent login.
pam_securetty.so
Controls which TTYs root may log in; if misconfigured, console login can be blocked.
pam_deny.so
Why wrong: Explicitly denies access; would block all logins.
pam_unix.so
Why wrong: Handles authentication; misconfiguration would affect all logins.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
pam_securetty.so
The pam_securetty.so module restricts root login to terminals listed in /etc/securetty. If this file was misconfigured or the module is incorrectly set to 'required' for all users, local console and graphical display manager logins (which use virtual terminals like tty1) would be denied, while SSH (which uses pseudo-terminals like pts/0) would still succeed because pam_securetty.so typically does not apply to SSH sessions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
pam_limits.so
Why it's wrong here
Sets limits but does not prevent login.
pam_securetty.so
Why this is correct
Controls which TTYs root may log in; if misconfigured, console login can be blocked.
Related concept
Read the scenario before looking for a memorised answer.
pam_deny.so
Why it's wrong here
Explicitly denies access; would block all logins.
pam_unix.so
Why it's wrong here
Handles authentication; misconfiguration would affect all logins.
Common exam traps
The trap here is that candidates confuse pam_securetty.so with pam_access.so or assume SSH is also blocked, but pam_securetty.so specifically targets local TTYs and does not affect SSH pseudo-terminals by default.
Detailed technical explanation
pam_securetty.so checks the tty name against /etc/securetty, which typically lists only physical terminals (e.g., tty1-tty6). Graphical display managers (e.g., GDM, LightDM) often start on tty7 or use a different session type, and if the module is set to 'required' without proper exceptions, those logins fail. A common real-world scenario is after a system update or manual edit of /etc/securetty that accidentally removes all entries, causing root to be locked out of all local consoles while SSH remains accessible.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: pam_securetty.so — The pam_securetty.so module restricts root login to terminals listed in /etc/securetty. If this file was misconfigured or the module is incorrectly set to 'required' for all users, local console and graphical display manager logins (which use virtual terminals like tty1) would be denied, while SSH (which uses pseudo-terminals like pts/0) would still succeed because pam_securetty.so typically does not apply to SSH sessions.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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