It's good detective work. What you need to know about logging in Logging in is a series of steps. When you can't log in, there are still things that you can check and fix. Problems with commands are usually problems with the pointers to this full pathname. What you need to know about sharing files On a multiuser system, you can potentially share any file with any other user.
File permissions are security measures that determine who can share what files.
On a multiuser system, you share disk space and processing time with other users. Sooner or later, you'll need to know what to do to optimize your use of these resources.