The command ssh -i "ABC-key.pem" [email protected] would allow the administrator to connect securely to the remote server in order to install application software. The ssh command is a tool for establishing secure and encrypted connections between remote systems. The -i option specifies the identity file that contains the private key for key-based authentication. The "ABC-key.pem" is the name of the identity file that contains the private key. The [email protected] is the username and the IP address of the remote server. The command ssh -i "ABC-key.pem" [email protected] will connect to the remote server using the private key and allow the administrator to install application software. This is the correct command to use to connect securely to the remote server. The other options are incorrect because they either do not use key-based authentication (sftp [email protected] or telnet 10.0.0.1 80) or do not use the correct syntax for the command (scp "ABC-key.pem" [email protected] instead of scp -i "ABC-key.pem" [email protected] or sftp "ABC-key.pem" [email protected] instead of sftp -i "ABC-key.pem" [email protected]). Reference: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 17: Implementing Basic Security, page 513.

The remediation step that will prevent the web service from running as a privileged user is adding the User=webservice to the [Service] section of the service file. The service file is a configuration file that defines the properties and behavior of a systemd service. The systemd is a system and service manager that controls the startup and operation of Linux systems. The service file contains various sections and options that specify how the service should be started, stopped, and managed. The [Service] section defines how the service should be executed and what commands should be run. The User option specifies the user name or ID that the service should run as. The webservice is the name of the user that the administrator wants to run the web service as. The administrator should add the User=webservice to the [Service] section of the service file, which will prevent the web service from running as a privileged user, such as root, and improve the security of the system. This is the correct remediation step to use to prevent the web service from running as a privileged user. The other options are incorrect because they either do not change the user that the service runs as (removing the ExecStart=/usr/sbin/webserver -D OPTIONS from the service file or updating the EnvironmentFile line in the [Service] section to /home/webservice/config) or do not affect the user that the service runs as (changing the multi-user.target in the [Install] section to basic.target). Reference: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 15: Managing System Services, page 458.

The command umask 002 will accomplish the task of reconfiguring the server so that only file owners and group members can modify new files by default. The umask command is a tool for setting the default permissions for new files and directories on Linux systems. The umask value is a four-digit octal number that represents the permissions that are subtracted from the default permissions. The default permissions for files are 666, which means read and write for owner, group, and others. The default permissions for directories are 777, which means read, write, and execute for owner, group, and others. The umask value consists of four digits: the first digit is for special permissions, such as setuid, setgid, and sticky bit; the second digit is for the owner permissions; the third digit is for the group permissions; and the fourth digit is for the others permissions. The umask value can be calculated by subtracting the desired permissions from the default permissions. For example, if the desired permissions for files are 664, which means read and write for owner and group, and read for others, then the umask value is 002, which is 666 - 664. The command umask 002 will set the umask value to 002, which will ensure that only file owners and group members can modify new files by default. This is the correct command to use to accomplish the task. The other options are incorrect because they either do not set the default permissions for new files (chmod 775 or chown -cf) or do not exist (chattr -Rv). Reference: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11: Managing File Permissions and Ownership, page 349.

The correct command to list all local accounts in which the UID is greater than 500 is:
awk -F: '$3 > 500 {print $1}' /etc/passwd
This command uses awk to process the /etc/passwd file, which contains information about the local users on the system. The -F: option specifies that the fields are separated by colons. The $3 refers to the third field, which is the UID. The condition $3 > 500 filters out the users whose UID is greater than 500. The action {print $1} prints the first field, which is the username.
The other commands are incorrect because:
find /etc/passwd -size +500 will search for files that are larger than 500 blocks in size, not users with UID greater than 500.
cut -d: fl / etc/ passwd > 500 will cut the first field of the /etc/passwd file using colon as the delimiter, but it will not filter by UID or print only the usernames. The > 500 part will redirect the output to a file named 500, not compare with the UID.
sed '/UID/' /etc/passwd < 500 will use sed to edit the /etc/passwd file and replace any line that contains UID with 500, not list the users with UID greater than 500. The < 500 part will redirect the input from a file named 500, not compare with the UID.
Reference:
Linux List All Users In The System Command - nixCraft, section "List all users in Linux using /etc/passwd file".
Unix script getting users with UID bigger than 500 - Stack Overflow, section "Using awk".

Based on the output of the image sent by the user, Joe is unable to log in to the Linux system because his account has been locked due to too many failed login attempts. The pam_tally2 -u joe -r command will resolve this issue by resetting Joe's failed login counter to zero and unlocking his account. This command uses the pam_tally2 module to manage user account locking based on login failures. The usermod -s /bin/bash joe command will change Joe's login shell to /bin/bash, but this will not unlock his account. The passwd -u joe command will unlock Joe's password if it has been locked by passwd -l joe, but this will not reset his failed login counter or unlock his account if it has been locked by pam_tally2. The chage -E 90 joe command will set Joe's account expiration date to 90 days from today, but this will not unlock his account or reset his failed login counter. Reference: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Securing Linux Systems, page 537.