/usr/bin/mandb: fopen /var/cache/man/7935: Permission denied

Step 1: The command "/usr/bin/mandb" is executed.

Step 2: The "fopen" function is called with the file path "/var/cache/man/7935" and the mode "read" as parameters.

Step 3: The "fopen" function tries to open the file at the given path with the specified mode.

Step 4: The operating system checks if the user executing the command has the necessary permissions to access the file.

Step 5: If the user does not have the required permissions, the "fopen" function returns an error code indicating that permission is denied.

Step 6: The command "/usr/bin/mandb" receives the error code from the "fopen" function and reports the error message "Permission denied."

Please note that the explanation provided above assumes a basic understanding of file permissions in a Unix-like operating system, as well as the C programming language.