CompTIA Updated XK0-005 Exam Questions and Answers by aren

The error message no mutual signature algorithm indicates that the RSA key used is not compatible with the server’s SSH configuration — often due to deprecated RSA algorithms (e.g., RSA with SHA-1). Newer OpenSSH versions disable weak algorithms by default, requiring clients to use a modern key algorithm such as ECDSA or Ed25519.

Option A is ineffective; restarting the SSH service will not change the available algorithms.

Option C is irrelevant as it addresses root login, not user admin.

Option D is a good practice but doesn’t resolve algorithm mismatches.

Therefore, the administrator should generate a new key with a supported algorithm, such as ECDSA:

bash

ssh-keygen -t ecdsa

This is supported by CompTIA Linux+ XK0-005 Study Guide under:

Domain 3.0: Security – “Secure Shell (SSH) Configuration”

"OpenSSH may reject older RSA keys due to disabled SHA-1 signatures. Keys using ECDSA or Ed25519 are recommended for compatibility and stronger security."

The chgrp command is used to change the group ownership of files and directories. By using this command, the administrator can assign the files in the newly created directory to the human resources group, which will allow the users in that group to access them. The other commands are not relevant for this task. For example:

chattr is used to change the file attributes, such as making them immutable or append-only1.

chage is used to change the password expiration information for a user account2.

chcon is used to change the security context of files and directories, which is related to SELinux3.

The +t option sets the "sticky bit" on a directory, which restricts deletion or renaming of files in the directory to the file's owner or the root user. This is commonly used in shared directories like /tmp, where multiple users may have access, but only the file owner should be allowed to modify their own files. The command chmod +t /directory/ applies this permission.

The error indicates corrupted kernel/initrd files.

Booting via rescue media (D) allows recovery without data loss.

Once in rescue, the administrator can reinstall kernel packages (E) to restore /boot.

Single-user mode (C) won’t work unless the kernel loads.

Replacing hardware or reinstalling the OS (A, F) is excessive and unnecessary.

Swap (B) is unrelated to kernel boot issues.