5.2 Files and Directories

Files are a facility for storing and organizing information, analogous to paper documents. They’re organized into directories, which are called folders on some other systems. Let’s look at the organization of files on a Debian system:

/.

A simple / represents the root directory. All other files and directories are contained in the root directory. If you are coming from the DOS/Windows world, / is very similar to what C:is for DOS, that is the root of the filesystem. A notable difference between DOS and Linux however, is that DOS keeps several filesystems: C: (first hard disk), A: (first floppy disk), and D: (either CD-ROM or second hard disk), whereas Linux has all its files organized above the same / root.

/home/janeq.

This is the home directory of user “janeq.” Reading left to right, to get to this directory you start in the root directory, enter directory home, and then enter directory janeq.

/etc/X11/XF86Config.

This is the configuration file for the X Window system. It resides in the X11 subdirectory of the /etc directory. /etc is in turn a subdirectory of the root directory, /.

Things to note:

• Filenames are case-sensitive. That is, MYFILE and MyFile are different files.
• The root directory is referred to as simply /. Don’t confuse this “root” with the root user, the user on your system with “super powers.”
• Every directory has a name, which can contain any letters or symbols except /. The root directory is an exception; its name is / (pronounced “slash” or “the root directory”), and it cannot be renamed.
• While you can use almost any letters or symbols in a filename, in practice it’s a bad idea. It is better to avoid characters that often have special meanings on the command line, including: { } ( ) [ ] ’ ‘ " \/ > < | ; ! # & ^ * %
• Also avoid putting spaces in filenames. If you want to separate words in a name, good choices are the period, hyphen, and underscore. You could also capitalize each word, LikeThis.
• Each file or directory is designated by a fully-qualified filename, absolute filename, or path, giving the sequence of directories which must be passed through to reach it. The three terms are synonymous. All absolute filenames begin with the / directory, and there’s a / before each directory or file in the filename. The first / is the name of a directory, but the others are simply separators to distinguish the parts of the filename.
• The words used here can be confusing. Take the following example: /usr/share/keytables/us.map.gz. This is a fully-qualified filename; some people call it a path. However, people will also refer to us.map.gz alone as a filename.
• There is also another use for the word “path.” The intended meaning is usually clear from the context.
• Directories are arranged in a tree structure. All absolute filenames start with the root directory. The root directory has a number of branches, such as /etc and /usr. These subdirectories in turn branch into still more subdirectories, such as /etc/init.d and /usr/local. The whole thing together is called the “directory tree.”
• You can think of an absolute filename as a route from the base of the tree (/) to the end of some branch (a file). You’ll also hear people talk about the directory tree as if it were a family tree: Thus subdirectories have “parent,” and a path shows the complete ancestry of a file.
• There are also relative paths that begin somewhere other than the root directory. More on this later.
• No directory corresponds to a physical device, such as your hard disk. This differs from DOS and Windows, in which all paths begin with a device name such as C:\. The directory tree is meant to be an abstraction of the physical hardware, so you can use the system without knowing what the hardware is. All your files could be on one disk – or you could have 20 disks, some of them connected to a different computer elsewhere on the network. You can’t tell just by looking at the directory tree, and nearly all commands work just the same way no matter what physical device(s) your files are really on.

Don’t worry if all this isn’t completely clear yet. There are many examples to come.