This is the least destructive method of resetting the administrator password because it does not require modifying any files or reinstalling the OS. It only requires changing the boot parameters temporarily and running a command to change the password. Reference: https://wiki.archlinux.org/title/Reset_lost_root_password#Using_GRUB

The given output in the image indicates that the file is present, but the permissions may not allow it to be read.
The output indicates '-rw-------', which means that the file is set to be readable and writable by the owner only, with no permissions for group or others. To allow the file to be read by users other than the owner, the file's permissions will need to be changed. The chmod (change mode) command is used to change the file's permissions in Linux. For example, chmod 644 file would change the permissions of the file to be readable by everyone and writable by the owner, which is typically what's required for a file server. It is always recommended to apply the least permissive settings that still allow the required operation to maintain security.

The backup type that only records changes to the data blocks on a virtual machine is snapshot. A snapshot is a point-in-time copy of a virtual machine (VM) that captures the state and data of the VM at a specific moment. A snapshot can be created instantly and with minimal overhead, as it only stores the changes made to the VM after the snapshot was taken. A snapshot can be used to restore the VM to its previous state in case of data loss or corruption.

The administrator should close ports 21 and 23 to secure the server properly. Port 21 is used for FTP (File Transfer Protocol), which is an unsecure protocol that allows file transfer between a client and a server over a network connection. FTP does not encrypt the data or the credentials that are transmitted, making them vulnerable to interception or modification by attackers. Port 23 is used for Telnet, which is an unsecure protocol that allows remote login and command execution over a network connection using a CLI. Telnet does not encrypt the data or the credentials that are transmitted, making them vulnerable to interception or modification by attackers.