Quick Answer
The answer is to edit /etc/security/limits.conf and add the lines 'soft nofile 65536' and 'hard nofile 65536' to permanently increase open file limits in Linux. This works because the soft limit defines the current working threshold for file descriptors, while the hard limit sets the absolute maximum a user can raise it to without root privileges; setting both ensures the user can immediately use the higher value without additional ulimit commands. On the CompTIA Linux+ XK0-005 exam, this tests your understanding of PAM (Pluggable Authentication Modules) and system resource limits, often appearing as a scenario where a web application exhausts file descriptors. A common trap is confusing a temporary ulimit command with a permanent configuration change, or forgetting that limits.conf requires a logout/login to take effect. Memory tip: think "soft is now, hard is the ceiling"—both must be set to lock in the increase.
This XK0-005 practice question tests your understanding of system management. 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 runs a web application that frequently runs out of file descriptors. Which configuration change would permanently increase the maximum number of open files for all users?
Set 'fs.file-max = 65536' in /etc/sysctl.conf
Why wrong: Sets system limit, not per-user.
Add 'session required pam_limits.so' to /etc/pam.d/login
Why wrong: pam_limits.so is already included; this enables limits but doesn't set values.
Run 'ulimit -n 65536' in a startup script
Why wrong: Only affects current shell session.
Edit /etc/security/limits.conf and add 'soft nofile 65536' and 'hard nofile 65536'
Correct file and syntax.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Edit /etc/security/limits.conf and add 'soft nofile 65536' and 'hard nofile 65536'
Option D is correct because editing /etc/security/limits.conf with both 'soft nofile' and 'hard nofile' entries permanently raises the per-user limit on open file descriptors for all users (or specified users/groups) at login. The soft limit is the current working limit, while the hard limit is the maximum ceiling; setting both ensures the user can reach the desired value without needing to run ulimit with root privileges.
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.
Set 'fs.file-max = 65536' in /etc/sysctl.conf
Why it's wrong here
Sets system limit, not per-user.
Add 'session required pam_limits.so' to /etc/pam.d/login
Why it's wrong here
pam_limits.so is already included; this enables limits but doesn't set values.
Run 'ulimit -n 65536' in a startup script
Why it's wrong here
Only affects current shell session.
Edit /etc/security/limits.conf and add 'soft nofile 65536' and 'hard nofile 65536'
Why this is correct
Correct file and syntax.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse the system-wide kernel parameter 'fs.file-max' (Option A) with the per-user PAM limits in limits.conf, assuming that raising the kernel value alone will resolve per-process file descriptor exhaustion.
Detailed technical explanation
Under the hood, the per-user file descriptor limits are enforced by the PAM module pam_limits.so, which reads /etc/security/limits.conf at user login. The 'nofile' item controls the RLIMIT_NOFILE resource, which is a per-process limit; each process started by the user inherits these values. In real-world scenarios, a web application like Apache or Nginx may spawn many worker processes, and if the per-user soft limit is too low, the application will hit 'Too many open files' errors even if the system-wide fs.file-max is high.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
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FAQ
System Management — This question tests System Management — Read the scenario before looking for a memorised answer..
The correct answer is: Edit /etc/security/limits.conf and add 'soft nofile 65536' and 'hard nofile 65536' — Option D is correct because editing /etc/security/limits.conf with both 'soft nofile' and 'hard nofile' entries permanently raises the per-user limit on open file descriptors for all users (or specified users/groups) at login. The soft limit is the current working limit, while the hard limit is the maximum ceiling; setting both ensures the user can reach the desired value without needing to run ulimit with root privileges.
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 11, 2026
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