Starting a web site - 222 CHAPTER 14 UNDERSTANDING LINUX FILES AND
222 CHAPTER 14 UNDERSTANDING LINUX FILES AND USERS Note Groups are yet another reminder of Ubuntu s Unix origins. Unix is often used on huge computer systems with hundreds or thousands of users. By putting each user into a group, the system administrator s job is a lot easier. When controlling system resources, the administrator can control groups of users rather than hundreds of individual users. On most home user PCs, the concept of groups is a little redundant, because there s normally a single user, or at most, two or three. However, the concept of groups is central to the way that Linux handles files. A standard user account under Ubuntu is normally limited in what it can do. As a standard user, you can save files to your own private area of the disk, located in the /home directory, as shown in Figure 14-2, but usually nowhere else. You can move around the file system, but some directories are strictly out of bounds. In a similar way, some files can be opened as read-only, so you cannot save changes to them. All of this is achieved using file permissions. Figure 14-2. Your personal directory within home is your area on the hard disk. This is enforced via file permissions. Every file and directory is owned by a user. In addition, files and directories have three separate settings that indicate who within the Linux system can read them, who can write to them, and, if the file in question is runnable (usually a program or a script), who can run it ( execute it). In the case of directories, it s also possible to set who can browse them, as well as who can write files to them. If you try to access a file or directory for which you don t have permission, you ll be turned away with an access denied error message.