CompTIA XK0-005 Online Practice Questions and Exam Preparation

CompTIA XK0-005 Online Questions & Answers

• Question 161:

  A Linux systems administrator needs to persistently enable IPv4 forwarding in one of the Linux systems. Which of the following commands can be used together to accomplish this task? (Choose two.)

  A. sysctl net.ipv4.ip_forward
  B. sysctl -w net.ipv4.ip_forward=1
  C. echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf
  D. echo 1 > /proc/sys/net/ipv4/ip_forward
  E. sysctl -p
  F. echo "net.ipv6.conf.all.forwarding=l" >> /etc/sysctl.conf
  B. sysctl -w net.ipv4.ip_forward=1
  E. sysctl -p

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  Explanation

  The commands that can be used together to persistently enable IPv4 forwarding in one of the Linux systems are sysctl -w net.ipv4.ip_forward=1 and sysctl -p. The first command will use sysctl to write a new value (1) to the net.ipv4.ip_forward kernel parameter, which controls whether IP forwarding is enabled or disabled for IPv4. This will enable IP forwarding immediately without rebooting. However, this change is temporary and will be lost after a reboot or a system reload. To make it permanent, we need to use the second command sysctl -p, which will load kernel parameters from /etc/sysctl.conf file. This file contains key-value pairs of kernel parameters and their values. To make sure that net.ipv4.ip_forward is set to 1 in this file, we can either edit it manually or append it using echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf.

  The other options are not correct commands for persistently enabling IPv4 forwarding. The sysctl net.ipv4.ip_forward command will only display the current value of net.ipv4.ip_forward parameter, but not change it. The echo 1 > /proc/sys/net/ipv4/ip_forward command will write 1 to /proc/sys/net/ipv4/ip_forward file, which is another way to change net.ipv4.ip_forward parameter. However, this change is also temporary and will not survive a reboot or a system reload. The echo "net.ipv6.conf.all.forwarding=l" >> /etc/sysctl.conf command will append a line to /etc/sysctl.conf file that sets net.ipv6.conf.all.forwarding parameter to 1. However, this parameter controls whether IP forwarding is enabled or disabled for IPv6, not IPv4.

  References: sysctl(8) - Linux manual page; Configure Linux as a Router (IP Forwarding)

• Question 162:

  A Linux administrator is scheduling a system job that runs a script to check available disk space every hour. The Linux administrator does not want users to be able to start the job. Given the following:

  

  The Linux administrator attempts to start the timer service but receives the following error message:

  

  Which of the following is MOST likely the reason the timer will not start?

  A. The checkdiskspace.timer unit should be enabled via systemct1.
  B. The timers.target should be reloaded to get the new configuration.
  C. The checkdiskspace.timer should be configured to allow manual starts.
  D. The checkdiskspace.timer should be started using the sudo command.
  C. The checkdiskspace.timer should be configured to allow manual starts.

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  Explanation

  The most likely reason the timer will not start is that the checkdiskspace.timer should be configured to allow manual starts. By default, systemd timers do not allow manual activation via systemct1 start, unless they have RefuseManualStart=no in their [Unit] section. This option prevents users from accidentally starting timers that are meant to be controlled by other mechanisms, such as calendar events or dependencies. To enable manual starts for checkdiskspace.timer, the administrator should add RefuseManualStart=no to its [Unit] section and reload systemd. The other options are not correct reasons for the timer not starting. The checkdiskspace.timer unit does not need to be enabled via systemct1 enable, because enabling a timer only makes it start automatically at boot time or after a system reload, but does not affect manual activation. The timers.target does not need to be reloaded to get the new configuration, because reloading a target only affects units that have a dependency on it, but does not affect manual activation. The checkdiskspace.timer does not need to be started using the sudo command, because the administrator is already running systemct1 as root, as indicated by the # prompt.

  References: systemd.timer(5) - Linux manual page; systemct1(1) - Linux manual page

• Question 163:

  During a security scan, the password of an SSH key file appeared to be too weak and was cracked. Which of the following commands would allow a user to choose a stronger password and set it on the existing SSH key file?

  A. passwd
  B. ssh
  C. ssh-keygen
  D. pwgen
  C. ssh-keygen

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  Explanation

  The command that would allow a user to choose a stronger password and set it on the existing SSH key file is ssh-keygen -p -f . This command uses the ssh-keygen tool, which is used to generate, manage, and convert authentication keys for SSH. The -p option stands for passphrase, and it allows the user to change or remove the passphrase of an existing private key file. The -f option specifies the filename of the key file. The command will prompt the user for the old passphrase, and then for the new passphrase twice. The other options are not correct commands for changing the password of an SSH key file. The passwd command is used to change the password of a user account on a Linux system, not an SSH key file. The ssh command is used to log in to a remote system using SSH, not to change the password of an SSH key file. The pwgen command is used to generate random passwords, not to change the password of an SSH key file.

  References: ssh-keygen(1) - Linux manual page; How To: Change Passphrase for SSH Private Key - Unix Tutorial

• Question 164:

  While troubleshooting server issues, a Linux systems administrator obtains the following output:

  [rootGhost ~]# totalfree -m usedfreesharedbuf f/cache available Mem:373635988824829

  Swap:20471824223

  Which of the following best describes the state of the system?

  A. The system has consumed the system memory and swap space.
  B. The system has enough free memory space.
  C. The system has swap disabled.
  D. The system has allocated enough buffer space.
  B. The system has enough free memory space.

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  Explanation

  The output shows that the system has a total of 3736MB of memory, of which 3598MB is free. This indicates that the system has enough free memory space12.

  References:1(https://phoenixnap.com/kb/swapspace)2(https://www.baeldung.com/linux/swap-space-use)

• Question 165:

  A systems administrator was tasked with assigning the temporary IP address/netmask 192.168.168.1/255.255.255.255 to the interface eth0 of a Linux server.

  When adding the address, the following error appears:

  # ip address add 192.168.168.1/33 dev eth0

  Error: any valid prefix is expected rather than "192.168.168.1/33".

  Based on the command and its output above, which of the following is the cause of the issue?

  A. The CIDR value /33 should be /32 instead.
  B. There is no route to 192.168.168.1/33.
  C. The interface eth0 does not exist.
  D. The IP address 192.168.168.1 is already in use.
  A. The CIDR value /33 should be /32 instead.

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  Explanation

  The cause of the issue is that the CIDR value /33 is invalid for an IPv4 address. The CIDR value represents the number of bits in the network prefix of an IP address, and it can range from 0 to 32 for IPv4 addresses. A CIDR value of /33 would imply a network prefix of more than 32 bits, which is impossible for an IPv4 address. To assign a temporary IP address/netmask of 192.168.168.1/255.255.255.255 to eth0, the CIDR value should be /32 instead, which means a network prefix of 32 bits and a host prefix of 0 bits. There is no route to 192.168.168.1/33 is not the cause of the issue, as the ip address add command does not check the routing table. The interface eth0 does not exist is not the cause of the issue, as the ip address add command would display a different error message if the interface does not exist. The IP address 192.168.168.1 is already in use is not the cause of the issue, as the ip address add command would display a different error message if the IP address is already in use.

  References: [CompTIA Linux+ (XK0-005) Certification Study Guide], Chapter 13: Networking Fundamentals, page 435.

• Question 166:

  A systems administrator is tasked with setting up key-based SSH authentication. In which of the following locations should the administrator place the public keys for the server?

  A. ~/.sshd/authkeys
  B. ~/.ssh/keys
  C. ~/.ssh/authorized_keys
  D. ~/.ssh/keyauth
  C. ~/.ssh/authorized_keys

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  Explanation

  The administrator should place the public keys for the server in the ~/.ssh/authorized_keys file. The SSH (Secure Shell) protocol is a method for establishing secure and encrypted connections between remote systems. The SSH protocol supports two types of authentication: password-based and key-based. Password-based authentication requires the user to enter the password of the remote system every time they connect. Key-based authentication requires the user to generate a pair of cryptographic keys: a public key and a private key. The public key is stored on the remote system, while the private key is kept on the local system. The public key and the private key are mathematically related, but not identical. The SSH protocol uses the keys to verify the identity of the user and establish a secure connection without requiring a password. The ~/.ssh/authorized_keys file is a file that contains the public keys of the users who are allowed to connect to the remote system using key-based authentication. The administrator should place the public keys for the server in this file, one per line, and set the appropriate permissions for the file. The administrator should also configure the SSH server to enable key-based authentication by editing the /etc/ssh/sshd_config file and setting the option PasswordAuthentication to no. The administrator should place the public keys for the server in the ~/.ssh/authorized_keys file. This is the correct answer to the question. The other options are incorrect because they are not the standard locations for the public keys for the server (~/.sshd/authkeys, ~/.ssh/keys, or ~/.ssh/keyauth).

  References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 17: Implementing Basic Security, page 513.

• Question 167:

  A Linux systems administrator is configuring a new filesystem that needs the capability to be mounted persistently across reboots. Which of the following commands will accomplish this task? (Choose two.)

  A. df -h /data
  B. mkfs.ext4 /dev/sdc1
  C. fsck /dev/sdc1
  D. fdisk -l /dev/sdc1
  E. echo "/data /dev/sdc1 ext4 defaults 0 0" >> /etc/fstab
  F. echo "/dev/sdc1 /data ext4 defaults 0 0" >> /etc/fstab
  B. mkfs.ext4 /dev/sdc1
  F. echo "/dev/sdc1 /data ext4 defaults 0 0" >> /etc/fstab

  ---

  Explanation

  "modify the /etc/fstab text file to automatically mount the new partition by opening it in an editor and adding the following line:

  /dev/ xxx 1 /data ext4 defaults 1 2

  where xxx is the device name of the storage device"

  https://learning.oreilly.com/library/view/mastering-linux-system/9781119794455/b01.xhtml To configure a new filesystem that needs the capability to be mounted persistently across reboots, two commands are needed: mkfs.ext4 /dev/sdc1 and echo "/dev/sdc1 /data ext4 defaults 0 0" >> /etc/fstab. The first command creates an ext4 filesystem on the device /dev/sdc1, which is the partition that will be used for the new filesystem. The second command appends a line to the /etc/fstab file, which is the configuration file that controls persistent mount points of filesystems. The line specifies the device name, the mount point (/data), the filesystem type (ext4), the mount options (defaults), and the dump and pass values (0 0). The other commands are incorrect because they either do not create or configure a filesystem, or they have wrong syntax or arguments.

  References: CompTIA Linux+ Study Guide, Fourth Edition, page 409-410, 414-415.

• Question 168:

  A systems engineer is adding a new 1GB XFS filesystem that should be temporarily mounted under /ops/app. Which of the following is the correct list of commands to achieve this goal?

  

  A. Option A
  B. Option B
  C. Option C
  D. Option D
  D. Option D

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  Explanation

  The list of commands in option D is the correct way to achieve the goal. The commands are as follows:

  fallocate -l 1G /ops/app.img creates a 1GB file named app.img under the /ops directory.

  mkfs.xfs /ops/app.img formats the file as an XFS filesystem. mount -o loop /ops/app.img /ops/app mounts the file as a loop device under the /ops/app directory. The other options are incorrect because they either use the wrong commands (dd or truncate instead of fallocate), the wrong options (-t or - f instead of -o), or the wrong order of arguments (/ops/app.img /ops/app instead of /ops/app /ops/app.img).

  References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter

  10: Managing Storage, pages 323-324.

• Question 169:

  A Linux administrator is creating a directory called CompTIA_doc, and it needs to switch to another location to perform some system-related tasks. Which of the following commands should the administrator use for this task?

  A. mkdir CompTIA_doc and cd CompTIA_doc
  B. mkdir CompTIA_doc + cd CompTIA_doc
  C. mkdir CompTIA_doc || cd CompTIA_doc
  D. mkdir CompTIA_doc andand cd CompTIA_doc
  D. mkdir CompTIA_doc andand cd CompTIA_doc

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  Explanation

• Question 170:

  A cloud engineer needs to launch a container named web-01 in background mode. Which of the following commands will accomplish this task?

  A. docker builder -f --name web-01 httpd
  B. docker load --name web-01 httpd
  C. docker ps -a --name web-01 httpd
  D. docker run -d --name web-01 httpd
  D. docker run -d --name web-01 httpd

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  Explanation

  The docker run -d --name web-01 httpd command will launch a container named web-01 in background mode. This command will create and start a new container from the httpd image, assign it the name web-01, and run it in detached mode (-d), which means the container will run in the background without attaching to the current terminal. The docker builder -f --name web-01 httpd command is invalid, as builder is not a valid docker command, and -f and --name are not valid options for docker build. The docker load --name web-01 httpd command is invalid, as load does not accept a --name option, and httpd is not a valid file name for load. The docker ps -a --name web-01 httpd command is invalid, as ps does not accept a --name option, and httpd is not a valid filter for ps.

  References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Virtualization and Cloud Technologies, page 499.