Quick Answer
The answer is /etc/pam.d/sshd. This is the correct file because Linux’s Pluggable Authentication Modules architecture stores per-service configuration in the /etc/pam.d/ directory, where the filename matches the service name exactly—so for the SSH daemon, the authentication order is defined in /etc/pam.d/sshd. This file lists the modules and their control flags (such as required, sufficient, or requisite) that PAM consults sequentially during an SSH login attempt, determining whether to grant or deny access. On the CompTIA Linux+ XK0-005 exam, this tests your understanding of PAM’s modular authentication flow; a common trap is confusing it with the global /etc/pam.conf file or the sshd_config file, which controls SSH behavior, not authentication order. Remember the simple rule: service-specific PAM files live in /etc/pam.d/ and take the service’s name—so for sshd, it’s /etc/pam.d/sshd. A quick memory tip: “PAM matches the daemon’s name in its own directory.”
This XK0-005 practice question tests your understanding of security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 server is configured to use Pluggable Authentication Modules (PAM). Which file is used to define the authentication order for the 'sshd' service?
/etc/authselect/sshd
Why wrong: authselect is a tool, but the PAM file is in /etc/pam.d/.
/etc/security/sshd
Why wrong: This is not a standard PAM configuration file.
/etc/pam.d/sshd
This is the correct PAM configuration file for the SSH daemon.
/etc/pam.d/login
Why wrong: This configures PAM for the login service, not sshd.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
/etc/pam.d/sshd
In Linux, PAM configuration files for individual services are stored in /etc/pam.d/, with the filename matching the service name. For the sshd service, the file /etc/pam.d/sshd defines the authentication order, including the modules and their control flags (e.g., required, sufficient) that PAM will consult during SSH login. This is the standard location per the Linux PAM architecture, as documented in the pam.conf man page.
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.
/etc/authselect/sshd
Why it's wrong here
authselect is a tool, but the PAM file is in /etc/pam.d/.
/etc/security/sshd
Why it's wrong here
This is not a standard PAM configuration file.
/etc/pam.d/sshd
Why this is correct
This is the correct PAM configuration file for the SSH daemon.
Related concept
Read the scenario before looking for a memorised answer.
/etc/pam.d/login
Why it's wrong here
This configures PAM for the login service, not sshd.
Common exam traps
CompTIA often tests the distinction between /etc/pam.d/sshd and /etc/pam.d/login, as candidates may confuse the SSH service file with the general login file, especially since both handle authentication but for different services.
Detailed technical explanation
PAM uses a modular architecture where each service file in /etc/pam.d/ contains a stack of modules (e.g., pam_unix.so, pam_sss.so) with control flags like 'required', 'requisite', 'sufficient', or 'optional'. The order of these modules determines the authentication flow; for example, if pam_sss.so is listed before pam_unix.so, systemd-logind or SSSD authentication is attempted first. In real-world scenarios, misconfiguring the order in /etc/pam.d/sshd can lock out SSH access entirely, requiring console or out-of-band recovery.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the XK0-005 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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: /etc/pam.d/sshd — In Linux, PAM configuration files for individual services are stored in /etc/pam.d/, with the filename matching the service name. For the sshd service, the file /etc/pam.d/sshd defines the authentication order, including the modules and their control flags (e.g., required, sufficient) that PAM will consult during SSH login. This is the standard location per the Linux PAM architecture, as documented in the pam.conf man page.
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 30, 2026
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