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We touched on the idea of file system shortcuts in 9, when we discussed creating launchers on the GNOME desktop. The problem with launchers is that they are recognized only within GNOME. In other words, they mean nothing when you re using the command prompt (or virtually any other program that loads/saves files, with the exception of some programs created specially for the GNOME desktop environment). The Ubuntu file system offers two types of genuine shortcuts, which it refers to as file links. They are symbolic links and hard links. Symbolic links are the most commonly used. A symbolic link is similar to a Windows shortcut in that a small file is created that points toward another file. Unlike a Windows shortcut, however, the symbolic link isn t a real file it exists at the file system level, so it can t be viewed in a text editor, for example. You can spot a symbolic link in a file listing in Nautilus because it has a small arrow pointing upward and to the right, and if you are in List view, the Type column indicates that it is a link to a file. If you right-click the link and open its Properties window, you can see on the Basic tab the field link target to find out which is the original file. A hard link is more complex and requires some understanding of how files work. In simple terms, all files consist of a pointer and actual data. As you might expect, the pointer tells the file system where on the disk to find the data. Creating a hard link effectively creates an additional pointer to the data that has exactly the same attributes as the original pointer, except with a different name. Performing any operation on the linked file will perform that operation on the original file. Additionally, there will be no obvious sign that the hard link isn t a genuine file, apart from the fact that the link count a property of files will be greater than 1. This indicates that more than one file links to the data. Maybe now you can see why people prefer to use the more obviously detectable symbolic links! To create a symbolic link, just right-click a file and select the option Make Link. You can move the link wherever you want; it will still point to the correct file. The new link has odd file permissions. It claims to have Read/Write/Execute permissions for everybody (rwxrwxrwx), but actually, because it s a link, it mirrors the permissions of the file it links to. So if you attempt to access a shortcut that links to a file you don t have permission to access, you ll see the appropriate error message.

Summary

In this chapter you got to know two important elements of the Ubuntu experience, largely derived from its UNIX and Linux predecessors: users and permissions. These are important concepts that lay the foundation of the security implemented in Ubuntu. Through users, people can have their own experiences, configurations, data, and permissions. An important characteristic is that every user account can have its own files and set permissions on them. What files a user can change determines in brief what that user can do with the system. We discussed the differences between root and standard users, and how to allow temporary access to root s privileges. We showed you the steps to create users and group accounts, and investigated the sometimes puzzling notation for file and folder permissions. Once you ve mastered the basics, you should be ready to set permissions on your own.