Hello! This icon means that your user cannot work with it (linux has read, write, view and execute access rights related to files and folders separately). You have to execute the command from the root user (this user has access to all files and folders, even system ones, so you have to be careful with him so as not to break the system, but in this case you will not break). First, log in to the root user using the su - command, enter the password, and then execute the command. Or you can just use sudo before the command (then you will also need to enter the password), but in some distributions sudo is disabled due to security reasons (how to enable it is easy to Google).