CompTIA Linux+ (XK0-006) — Questions and Answers

Question 1: Which systemd unit type is responsible for mounting filesystems during boot?

.socket
.service
.mount (Correct answer)
.path

Correct answer: .mount

.mount units correspond to filesystem mount points and are generated from /etc/fstab entries.

Question 2: What does `read -r line` do differently from `read line` in bash?

Prevents backslash from being treated as an escape character (Correct answer)
Reads from a file instead of stdin
Reads the line in reverse order
Reads only a single character

Correct answer: Prevents backslash from being treated as an escape character

The `-r` flag disables backslash interpretation, so backslashes are read literally — essential for reading file paths.

Question 3: What is the purpose of the `tcpdump` tool in Linux network security?

Tests TCP connection speeds
Captures and analyzes network packets in real time (Correct answer)
Dumps network interface configuration
Monitors TCP connection states in the kernel

Correct answer: Captures and analyzes network packets in real time

tcpdump is a packet capture tool that intercepts and displays network traffic, essential for troubleshooting and security analysis.

Question 4: Which factor MOST significantly affects the quality of technical outcomes in Linux practice?

The brand of equipment being used
The practitioner's training, preparation, and attention to detail (Correct answer)
The speed at which procedures are completed
The time of day the procedure is performed

Correct answer: The practitioner's training, preparation, and attention to detail

The quality of technical outcomes depends primarily on the practitioner's level of training, thorough preparation, and careful attention to detail. While equipment matters, the professional's competence is the most significant factor.

Question 5: Which `getopts` call correctly processes a flag `-v` and an option `-o` that takes an argument?

getopts "v:o" opt
getopts "v|o:" opt
getopts "-v -o:" opt
getopts "vo:" opt (Correct answer)

Correct answer: getopts "vo:" opt

In `getopts`, a colon after a letter means it takes an argument; `vo:` means `-v` is a flag and `-o` requires a value.

Question 6: What is the purpose of the `tune2fs` command?

Tunes system performance by adjusting kernel parameters
Converts ext2 to ext4 filesystem
Adjusts tunable parameters of ext2/3/4 filesystems, such as reserved block count, check intervals, and mount options (Correct answer)
Tunes RAID parameters for ext filesystems

Correct answer: Adjusts tunable parameters of ext2/3/4 filesystems, such as reserved block count, check intervals, and mount options

tune2fs modifies ext2/3/4 filesystem parameters without reformatting, including reserved space percentage, mount count limits, and filesystem features.

Question 7: What does `ls -d */` display?

Symbolic links only
All files including hidden ones
Files sorted by directory
Only directories in the current location (Correct answer)

Correct answer: Only directories in the current location

`ls -d */` matches and lists only directories (the trailing slash selects directories, `-d` prevents recursion).

Question 8: What role does calibration play in maintaining technical accuracy for Linux professionals?

It is only necessary for new equipment
It is an optional best practice for advanced professionals
It only matters during formal inspections
It ensures instruments and methods produce accurate, consistent results over time (Correct answer)

Correct answer: It ensures instruments and methods produce accurate, consistent results over time

Regular calibration ensures that instruments, tools, and methods continue to produce accurate and consistent results over time. Without calibration, measurement drift and equipment wear can lead to unreliable outcomes.

Question 9: In Linux practice, what is the CORRECT sequence when performing a technical procedure?

Document, execute, then plan
Execute, then plan and review
Plan, prepare, execute, verify, and document (Correct answer)
Execute immediately and document only if issues arise

Correct answer: Plan, prepare, execute, verify, and document

The correct sequence follows a systematic approach: plan the procedure, prepare necessary resources, execute according to standards, verify results meet specifications, and document the process and outcomes. This ensures quality and accountability.

Question 10: Which command installs and activates fail2ban to protect SSH from brute-force attacks?

fail2ban-client start sshd
systemctl enable --now fail2ban (Correct answer)
service fail2ban install && start
apt install fail2ban --activate-ssh

Correct answer: systemctl enable --now fail2ban

After installing fail2ban, systemctl enable --now fail2ban starts the service immediately and enables it at boot.

Question 11: When a Linux professional faces pressure to compromise professional standards, the BEST response is to:

Immediately resign from the position
Document the pressure and uphold professional standards (Correct answer)
Ignore the pressure and continue without reporting
Comply to maintain workplace relationships

Correct answer: Document the pressure and uphold professional standards

Professionals should document any pressure to compromise standards and continue upholding their professional obligations. Documentation creates a record of the situation while maintaining ethical integrity.

Question 12: What does `set -u` do in a bash script?

Enables Unicode support
Updates the PATH variable
Treats unset variables as an error when they are expanded (Correct answer)
Unsets all variables

Correct answer: Treats unset variables as an error when they are expanded

`set -u` causes the script to exit with an error if an unset variable is referenced, catching typos early.

Question 13: In SELinux, what does the 'enforcing' mode do to policy violations?

Only logs to audit.log without blocking
Blocks and logs violations (Correct answer)
Disables all network policies
Logs violations but allows them

Correct answer: Blocks and logs violations

Enforcing mode actively blocks actions that violate SELinux policy and records denials in the audit log.

Question 14: In Linux certification, what does redundancy in system design primarily provide?

Increased complexity
Simplified maintenance
Fault tolerance and high availability (Correct answer)
Lower initial cost

Correct answer: Fault tolerance and high availability

Redundancy provides fault tolerance by ensuring that if one component fails, backup components maintain system availability.

Question 15: Which command displays the process tree showing parent-child relationships?

procstat
pstree (Correct answer)
top -H
ps -ef

Correct answer: pstree

pstree displays running processes as a tree, visually showing parent-child relationships between processes.

Question 16: What role does calibration play in maintaining technical accuracy for Linux professionals?

It ensures instruments and methods produce accurate, consistent results over time (Correct answer)
It is an optional best practice for advanced professionals
It is only necessary for new equipment
It only matters during formal inspections

Correct answer: It ensures instruments and methods produce accurate, consistent results over time

Question 17: Which option makes `apt-get` automatically remove packages that were installed as dependencies but are no longer needed?

apt-get remove --auto
apt-get clean
apt-get purge --orphans
apt-get autoremove (Correct answer)

Correct answer: apt-get autoremove

`apt-get autoremove` removes orphaned dependency packages that are no longer required by any installed package.

Question 18: How do you append a line to a file inside a shell script without overwriting it?

echo 'line' > file
echo 'line' | file
echo 'line' >> file (Correct answer)
echo 'line' >| file

Correct answer: echo 'line' >> file

`>>` appends to a file; `>` truncates and overwrites.

Question 19: What does the 'umask 027' command do?

Sets the maximum permission to 027
Removes all permissions from new files
Makes all new files executable
New files get permissions 640 and new directories get 750 (Correct answer)

Correct answer: New files get permissions 640 and new directories get 750

umask 027 masks out write for group and all permissions for others, resulting in 640 for files and 750 for directories.

Question 20: When a Linux professional encounters an unexpected result during a technical procedure, the FIRST action should be to:

Continue the procedure and address it later
Repeat the procedure from the beginning immediately
Report the issue without any preliminary assessment
Stop, assess the situation, and determine whether to proceed or seek guidance (Correct answer)

Correct answer: Stop, assess the situation, and determine whether to proceed or seek guidance

Stopping to assess the situation when unexpected results occur is critical. This allows the professional to evaluate whether it is safe and appropriate to continue, and to determine if additional guidance or resources are needed.

Question 21: What does 'find / -perm -4000' search for?

Files readable by all users
Files with the SUID bit set (Correct answer)
World-writable files
Files owned by root

Correct answer: Files with the SUID bit set

-perm -4000 matches files where the SUID bit (4000) is set, which can be a privilege escalation risk.

Question 22: Which boot parameter disables all CPU mitigations for Spectre/Meltdown vulnerabilities, sometimes used for performance testing?

cpu.mitigations=none
nosecurity=1
mitigations=off (Correct answer)
nopti nospectre_v2

Correct answer: mitigations=off

The mitigations=off kernel parameter is a single flag that disables all CPU vulnerability mitigations (available since Linux 5.2).

Question 23: Which nmap flag performs a SYN (stealth) scan without completing the TCP handshake?

-sS (Correct answer)
-sT
-sA
-sU

Correct answer: -sS

nmap -sS sends SYN packets and never completes the handshake, making the scan less likely to appear in connection logs.

Question 24: In Linux, what is the PRIMARY purpose of conducting regular safety drills and exercises?

To ensure personnel can respond effectively in emergencies (Correct answer)
To evaluate employee performance reviews
To satisfy insurance requirements only
To reduce daily workload

Correct answer: To ensure personnel can respond effectively in emergencies

Regular safety drills ensure that all personnel are prepared to respond effectively during actual emergencies. Practice builds muscle memory, identifies gaps in emergency procedures, and improves overall response times.

Question 25: Which iptables table is used for Network Address Translation (NAT)?

mangle
filter
nat (Correct answer)
raw

Correct answer: nat

The nat table handles NAT operations including SNAT, DNAT, and MASQUERADE in the PREROUTING and POSTROUTING chains.

Question 26: In nftables, what keyword is used to create a stateful firewall rule accepting established and related traffic?

ct state { established, related } accept (Correct answer)
match state established related permit
conntrack state=ESTABLISHED,RELATED -j ACCEPT
state established,related ACCEPT

Correct answer: ct state { established, related } accept

nftables uses 'ct state' (connection tracking state) with set notation to match multiple states in one expression.

Question 27: When a Linux professional encounters an unexpected result during a technical procedure, the FIRST action should be to:

Report the issue without any preliminary assessment
Repeat the procedure from the beginning immediately
Stop, assess the situation, and determine whether to proceed or seek guidance (Correct answer)
Continue the procedure and address it later

Correct answer: Stop, assess the situation, and determine whether to proceed or seek guidance

Question 28: What does `$(command)` do in a shell script?

Pipes command output to /dev/null
Captures the command's stdout as a string (Correct answer)
Executes the command in the background
Runs the command in a subshell and discards output

Correct answer: Captures the command's stdout as a string

Command substitution `$(...)` replaces itself with the standard output of the enclosed command.

Question 29: What is the purpose of the UFW (Uncomplicated Firewall) command `ufw enable`?

Reloads the firewall rules without enabling it
Activates the firewall and enables it to start on boot (Correct answer)
Only enables the firewall for the current session
Creates a default allow-all policy

Correct answer: Activates the firewall and enables it to start on boot

ufw enable both activates the firewall immediately and configures it to start automatically on system boot.

Question 30: What is the purpose of the /etc/sudoers file?

Store hashed passwords for sudo users
Define which users can run commands as root or another user (Correct answer)
Log all sudo command executions
Set password expiration policies

Correct answer: Define which users can run commands as root or another user

/etc/sudoers specifies user and group privileges for running commands via sudo.

CompTIA Linux+ (XK0-006)

CompTIA Linux+ certifies foundational Linux administration skills for IT professionals, covering system management, security, scripting/automation, and troubleshooting of Linux-based environments.

Questions

35 min

Time Limit

72%

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