The CompTIA Linux+ V8 Exam (XK0-006)

DNS client configuration is a foundational Linux networking task covered in Linux+ V8 system management objectives. When an administrator needs to specify the IP address of a DNS server that the system should use for name resolution, the correct file to modify is /etc/resolv.conf .

The /etc/resolv.conf file defines DNS resolver settings, including one or more nameserver entries that specify the IP addresses of DNS servers. Applications and system services rely on this file to resolve hostnames to IP addresses.

The other options are incorrect. /etc/whois.conf configures WHOIS queries. /etc/nsswitch.conf controls the order of name resolution sources but does not define DNS server IP addresses. /etc/dnsmasq.conf configures a local DNS caching service, not the system-wide resolver directly.

Linux+ V8 documentation highlights /etc/resolv.conf as the authoritative DNS client configuration file, though it may be dynamically managed by tools such as NetworkManager or systemd-resolved.

Therefore, the correct answer is B. /etc/resolv.conf .

To create an appropriate device label, format and create an ext4 file system on the new partition, you can use the following commands:

To create a GPT (GUID Partition Table) label on the new drive /dev/sdc, you can use the parted command with the -s option (for script mode), the device name (/dev/sdc), the mklabel command, and the label type (gpt). The command is:

parted -s /dev/sdc mklabel gpt

To create a primary partition of 10 GB on the new drive /dev/sdc, you can use the parted command with the -s option, the device name (/dev/sdc), the mkpart command, the partition type (primary), the file system type (ext4), and the start and end points of the partition (1 and 10G). The command is:

parted -s /dev/sdc mkpart primary ext4 1 10G

To format and create an ext4 file system on the new partition /dev/sdc1, you can use the mkfs command with the file system type (ext4) and the device name (/dev/sdc1). The command is:

mkfs.ext4 /dev/sdc1

You can verify that the new partition and file system have been created by using the lsblk command, which will list all block devices and their properties.

Password management is a core topic in the Security domain of CompTIA Linux+ V8. Password expiry policies are implemented to reduce the risk associated with long-lived credentials.

The primary reason for enforcing password expiration is to mitigate the risk of exposed or compromised passwords. If a password is leaked through phishing, malware, keylogging, or data breaches, limiting its lifespan reduces the window of opportunity for attackers to exploit it. Requiring periodic password changes ensures that compromised credentials eventually become invalid.

Option B correctly captures this security objective. Linux+ V8 documentation emphasizes minimizing credential exposure as a key principle of access control.

The other options are secondary or incorrect. Avoiding password reuse and increasing complexity are addressed through password history and complexity policies, not expiration alone. Password expiry does not force passwordless authentication, making option C incorrect.

Therefore, the correct answer is B. To mitigate the use of exposed passwords.

Comprehensive and Detailed 250 to 350 words of Explanation From Linux+ V8 documents:

Passwordless authentication using SSH key pairs is a foundational security practice covered in the Security domain of CompTIA Linux+ V8. It allows administrators to securely authenticate between systems without transmitting passwords over the network, significantly reducing the risk of credential compromise.

The correct approach involves two essential steps : generating an SSH key pair and installing the public key on the remote system. Option A correctly performs both steps using best-practice commands.

The command ssh-keygen -t rsa generates an RSA public/private key pair in the user’s ~/.ssh/ directory. The private key (id_rsa) remains securely on the local system, while the public key (id_rsa.pub) is intended to be shared. The second part of the command, ssh-copy-id -i ~/.ssh/id_rsa.pub john@server2, securely copies the public key to the remote server’s ~/.ssh/authorized_keys file. This enables key-based authentication for the specified user.

The other options are incorrect or incomplete. Option B uses ssh-keyscan, which is intended for collecting host keys to populate known_hosts, not for user authentication. Option C misuses ssh-agent, which manages keys already generated and does not create or install them. Option D is insecure and incorrect because copying the entire .ssh directory risks exposing private keys and violates security best practices.

Linux+ V8 documentation emphasizes the use of ssh-keygen and ssh-copy-id as the standard, secure method for configuring passwordless SSH access. This approach ensures proper permissions, correct key placement, and minimal risk.

This scenario represents a name resolution failure , which is a common troubleshooting case addressed in CompTIA Linux+ V8. The critical clues are the error messages returned by both curl and dig.

The curl error “Could not resolve host” indicates that the system is unable to translate the hostname into an IP address. This is confirmed by the dig output, which returns NXDOMAIN , meaning the DNS resolver cannot resolve the requested domain name. Importantly, the dig output shows that the query is reaching a DNS server (10.255.255.254), but the resolution fails, strongly pointing to a DNS client configuration issue .

Option C , reviewing and fixing the DNS client configuration file (such as /etc/resolv.conf or systemd-resolved settings), is the correct action. Linux+ V8 documentation highlights DNS misconfiguration as a primary cause of application connectivity issues. Incorrect nameserver entries, unreachable DNS servers, or misconfigured resolvers commonly produce NXDOMAIN responses.

The other options are incorrect. Firewall issues would result in connection timeouts, not DNS resolution failures. Requesting a new API endpoint is unnecessary without first confirming local DNS functionality. Internet connectivity issues would typically prevent any DNS communication, but here a DNS server is clearly being contacted.

Linux+ V8 stresses a layered troubleshooting approach: verify DNS resolution before investigating network ports or application logic. Therefore, the correct answer is C. Review and fix the DNS client configuration file .

IP packet forwarding is a key networking function in Linux system management and is explicitly referenced in the Linux+ V8 objectives. Enabling this feature allows a Linux system to act as a router by forwarding packets between network interfaces.

The kernel parameter responsible for this behavior is net.ipv4.ip_forward. When this parameter is set to 1, the Linux kernel allows IPv4 packets to be forwarded between interfaces. By default, this setting is often disabled on non-routing systems for security reasons.

The parameter can be modified temporarily using the sysctl command or permanently by editing /etc/sysctl.conf or files under /etc/sysctl.d/. Linux+ V8 documentation highlights this parameter as essential for configuring routing, NAT, and firewall-based gateway systems.

The other options are incorrect. net.ipv4.ip_multicast controls multicast behavior, not packet forwarding. net.ipv4.ip_route is not a valid kernel parameter. net.ipv4.ip_local_port_range defines the range of ephemeral ports used by outgoing connections and has no effect on routing.

Properly enabling IP forwarding is critical when configuring VPN gateways, firewalls, and network appliances. Therefore, the correct answer is D. net.ipv4.ip_forward .

Log monitoring is a common troubleshooting task in Linux system administration, and Linux+ V8 covers command-line tools for real-time log analysis. The requirement in this scenario is twofold: view log entries as they occur and simultaneously save them to another file.

The command tail -f /var/log/apache2/error.log | tee logfile.txt fulfills both requirements. The tail -f command follows the log file in real time, displaying new entries as they are written. The pipe (|) sends this output to the tee command, which writes the data to logfile.txt while also displaying it on standard output .

The other options are insufficient. Option A redirects output to a file but prevents real-time viewing. Option C appends output but still suppresses terminal display. Option B is syntactically invalid and does not use a proper command for writing output.

Linux+ V8 documentation specifically references tee as a useful utility for duplicating command output streams. This makes option D the correct and most effective solution.

Shell variable expansion is a fundamental scripting concept included in Linux+ V8 objectives. In Bash and similar shells, variables are expanded only when they are interpreted within double quotes or unquoted contexts, and sometimes explicit syntax is required to avoid ambiguity.

The correct notation is ${num}, as shown in option D. Using curly braces around the variable name ensures the shell correctly identifies the variable boundary, especially when it is adjacent to other characters. This guarantees proper expansion of the variable’s value.

The other options are incorrect. Single quotes prevent variable expansion entirely. The $(...) syntax is used for command substitution, not variable expansion. Quoting the variable name itself also prevents expansion.

Linux+ V8 documentation emphasizes ${VAR} notation as a best practice in shell scripting for clarity and correctness. Therefore, the correct answer is D.

For normal users to change their own password, /bin/passwd must have the SUID bit set (permissions should be -rwsr-xr-x). The SUID bit allows users to run the program with the permissions of the file owner (root), which is required to update /etc/shadow. The provided output shows /bin/passwd does not have the SUID bit (no ' s ' in the owner’s execute field). As a result, user " test " receives an " Authentication token manipulation error " . The password can be changed as root, which confirms it ' s a permissions/SUID issue.

Other options:

B. If the password didn’t meet requirements, a different error would appear.

C. There is no minimum day limit preventing password change (see chage -l output).

D. The account and password are active (not disabled).