CompTIA CompTIA Certifications XK0-005 Questions & Answers

• Question 41:

  While inspecting a recently compromised Linux system, the administrator identified a number of processes that should not have been running:

  

  Which of the following commands should the administrator use to terminate all of the identified processes?

  A. pkill -9 -f "upload*.sh"

  B. kill -9 "upload*.sh"

  C. killall -9 -upload*.sh"

  D. skill -9 "upload*.sh"

  Correct Answer: A

  Explanation: The pkill -9 -f "upload*.sh" command will terminate all of the identified processes. This command will send a SIGKILL signal (-9) to all processes whose full command line matches the pattern "upload*.sh" (-f). This signal will force the processes to terminate immediately without giving them a chance to clean up or save their state. The kill -9 "upload*.sh" command is invalid, as kill requires a process ID (PID), not a pattern. The killall -9 "upload*.sh" command is incorrect, as killall requires an exact process name, not a pattern. The skill -9 "upload*.sh" command is incorrect, as skill requires a username or a session ID (SID), not a pattern. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 15: Managing Memory and Process Execution, page 470.

• Question 42:

  An engineer needs to insert a character at the end of the current line in the vi text editor. Which of the following will allow the engineer to complete this task?

  A. p

  B. r

  C. bb

  D. A E. i

  Correct Answer: D

  Explanation: The vi text editor is a popular and powerful tool for editing text files on Linux systems. The vi editor has two modes: command mode and insert mode. In command mode, the user can issue commands to manipulate the text, such

  as moving the cursor, deleting, copying, pasting, searching, replacing, and saving. In insert mode, the user can type text into the file. To switch from command mode to insert mode, the user can press various keys, such as i, a, o, I, A, or O.

  To switch from insert mode to command mode, the user can press the Esc key.

  To insert a character at the end of the current line in the vi editor, the user can press the A key in command mode. This will move the cursor to the end of the line and switch to insert mode. Then, the user can type the desired character and

  press Esc to return to command mode. The statement D is correct.

  The statements A, B, C, and E are incorrect because they do not perform the desired task. The p key in command mode will paste the previously copied or deleted text after the cursor. The r key in command mode will replace the character

  under the cursor with another character. The bb key in command mode will move the cursor back two words. The i key in command mode will switch to insert mode before the cursor. References: [How to Use vi Text Editor in Linux]

• Question 43:

  The group owner of the / home/ test directory would like to preserve all group permissions on files created in the directory. Which of the following commands should the group owner execute?

  A. chmod g+s /home/test

  B. chgrp test /home/test

  C. chmod 777 /home/test

  D. chown --hR test /home/test

  Correct Answer: A

  The correct answer is A. chmod g+s /home/test

  This command will set the setgid bit on the /home/test directory, which means that any file or subdirectory created in the directory will inherit the group ownership of the directory. This way, the group permissions on files created in the directory

  will be preserved. The chmod command is used to change the permissions of files and directories. The g+s option is used to set the setgid bit for the group.

  The other options are incorrect because:

  B. chgrp test /home/test

  This command will change the group ownership of the /home/test directory to test, but it will not affect the group ownership of files created in the directory. The chgrp command is used to change the group of files and directories. The test /

  home/test arguments are used to specify the new group and the target directory.

  C. chmod 777 /home/test

  This command will give read, write, and execute permissions to everyone (owner, group, and others) on the /home/test directory, but it will not affect the group ownership or permissions of files created in the directory. The chmod command is

  used to change the permissions of files and directories. The 777 argument is an octal number that represents the permissions in binary form.

  D. chown -hR test /home/test

  This command will change the owner and group of the /home/test directory and all its contents recursively to test, but it will not preserve the original group permissions on files created in the directory. The chown command is used to change

  the owner and group of files and directories. The -hR option is used to affect symbolic links and operate on all files and directories recursively. The test /home/test arguments are used to specify the new owner and group and the target

  directory.

  References:

  How to Set File Permissions Using chmod

  How to Use Chmod Command in Linux with Examples

  How to Use Chown Command in Linux with Examples

  [How to Use Chgrp Command in Linux with Examples]

• Question 44:

  A Linux engineer needs to block an incoming connection from the IP address 2.2.2.2 to a secure shell server and ensure the originating IP address receives a response that a firewall is blocking the connection. Which of the following commands can be used to accomplish this task?

  A. iptables -A INPUT -p tcp -- dport ssh -s 2.2.2.2 -j DROP

  B. iptables -A INPUT -p tcp -- dport ssh -s 2.2.2.2 -j RETURN

  C. iptables -A INPUT -p tcp -- dport ssh -s 2.2.2.2 -j REJECT

  D. iptables -A INPUT -p tcp -- dport ssh -s 2.2.2.2 -j QUEUE

  Correct Answer: C

  The REJECT target sends back an error packet to the source IP address, indicating that the connection is refused by the firewall. This is different from the DROP target, which silently discards the packet without any response. The RETURN target returns to the previous chain, which may or may not accept the connection. The QUEUE target passes the packet to a userspace application for further processing, which is not the desired outcome in this case. References CompTIA Linux+ (XK0-005) Certification Study Guide, page 316 iptables - ssh - access from specific ip only - Server Fault, answer by Eugene Ionichev

• Question 45:

  A cloud engineer needs to change the secure remote login port from 22 to 49000. Which of the following files should the engineer modify to change the port number to the desired value?

  A. /etc/host.conf

  B. /etc/hostname

  C. /etc/services

  D. /etc/ssh/sshd_config

  Correct Answer: D

  Explanation: The file /etc/ssh/sshd_config contains the configuration settings for the SSH daemon, which handles the secure remote login. To change the port number, the engineer should edit this file and modify the line that says Port 22 to Port 49000. The other files are not related to the SSH service. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 13: Managing Network Services, page 411.

• Question 46:

  A User on a Linux workstation needs to remotely start an application on a Linux server and then forward the graphical display of that application back to the Linux workstation. Which of the following would enable the user to perform this action?

  A. ssh -X user@server application

  B. ssh -y user@server application

  C. ssh user@server application

  D. ssh -D user@server application

  Correct Answer: A

  The ssh -X option enables X11 forwarding, which allows the user to run graphical applications on the remote server and display them on the local workstation. The user needs to specify the username, the server address, and the application

  name after the ssh -X command. The remote server also needs to have X11Forwarding enabled and xauth installed for this to work.

  References:

  The web search result 8 explains how to run a GUI application through SSH by configuring both the SSH client and server.

  The web search result 6 provides a detailed answer on how to forward X over SSH to run graphics applications remotely, with examples and troubleshooting tips. The CompTIA Linux+ Certification Exam Objectives mention that the candidate

  should be able to "use SSH for remote access and management" as part of the System Operation and Maintenance domain1.

• Question 47:

  A systems administrator is gathering information about a file type and the contents of a file. Which of the following commands should the administrator use to accomplish this task?

  A. file filename

  B. touch filename

  C. grep filename

  D. lsof filename

  Correct Answer: A

  The file command is used to determine the type of a file by examining its contents. It can recognize many different formats, such as text, binary, executable, compressed, image, audio, video, etc. It can also display some additional information about the file, such as encoding, size, dimensions, etc12 References: 1: file(1) - Linux manual page 2: How to use the file command in Linux

• Question 48:

  The development team wants to prevent a file from being modified by all users in a Linux system, including the root account. Which of the following commands can be used to accomplish this objective?

  A. chmod / app/conf/file

  B. setenforce / app/ conf/ file

  C. chattr +i /app/conf/file

  D. chmod 0000 /app/conf/file

  Correct Answer: C

  The chattr command is used to change file attributes on Linux systems that support extended attributes, such as ext2, ext3, ext4, btrfs, xfs, and others. File attributes are flags that modify the behavior of files and directories.

  To prevent a file from being modified by all users in a Linux system, including the root account, the development team can use the chattr +i /app/conf/file command. This command will set the immutable attribute (+i) on the file /app/conf/file,

  which means that the file cannot be deleted, renamed, linked, appended, or written to by any user or process. To remove the immutable attribute, the development team can use the chattr -i /app/conf/file command. The statement C is correct.

  The statements A, B, and D are incorrect because they do not prevent the file from being modified by all users. The chmod /app/conf/file command does not work because it requires an argument to specify the permissions to change. The

  setenforce /app/conf/file command does not work because it is used to change the SELinux mode, not file attributes. The chmod 0000 /app/conf/file command will remove all permissions from the file, but it can still be modified by the root

  account. References: [How to Use chattr Command in Linux]

• Question 49:

  A Linux systems administrator is troubleshooting an I/O latency on a single CPU server. The administrator runs a top command and receives the following output:

  %Cpu(s): 0.2 us, 33.1 sy, 0.0 ni, 0.0 id, 52.4 wa, 0.0 hi, 0.2 si, 0.0 st

  Which of the following is correct based on the output received from the exe-cuted command?

  A. The server's CPU is taking too long to process users' requests.

  B. The server's CPU shows a high idle-time value.

  C. The server's CPU is spending too much time waiting for data inputs.

  D. The server's CPU value for the time spent on system processes is low.

  Correct Answer: C

  Explanation: The server's CPU is spending too much time waiting for data inputs. This can be inferred from the output of the top command, which shows the percentage of CPU time spent in different states. The wa state stands for wait, and it indicates that the CPU is idle while waiting for an I/O operation to complete. In this case, the wa state is 52.4%, which means that more than half of the CPU time is wasted on waiting for data inputs. This can cause a high I/O latency and affect the performance of the server. The other options are not correct based on the output received from the executed command. The server's CPU is not taking too long to process users' requests, because the us state, which stands for user, is only 0.2%, which means that the CPU is barely used by user processes. The server's CPU does not show a high idle-time value, because the id state, which stands for idle, is 0.0%, which means that the CPU is not idle at all. The server's CPU value for the time spent on system processes is not low, because the sy state, which stands for system, is 33.1%, which means that the CPU is heavily used by system processes. References: How to Use the Linux top Command (and Understand Its Output); [Understanding Linux CPU Load - when should you be worried?]

• Question 50:

  A systems administrator wants to be sure the sudo rules just added to /etc/sudoers are valid. Which of the following commands can be used for this task?

  A. visudo -c

  B. test -f /etc/sudoers

  C. sudo vi check

  D. cat /etc/sudoers | tee test

  Correct Answer: A

  Explanation: The command visudo -c can be used to check the validity of the sudo rules in the /etc/sudoers file. The visudo command is a tool for editing and validating the /etc/sudoers file, which defines the rules for the sudo command. The c option checks the syntax and logic of the file and reports any errors or warnings. The command visudo - c will verify the sudo rules and help the administrator avoid any mistakes. This is the correct command to use for this task. The other

  options are incorrect because they either do not check the validity of the file (test, sudo, or cat) or do not exist (sudo vi check). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18:

  Securing Linux Systems, page 546.