Concepts Glossary 158 Getting Started Guide Symbolic Link A symbolic link is a pointer from one file to another file. When you create a sym- bolic link, using the ln command, you can access a single file by referring to sev- eral different filenames, in different subdirectories of your filesystem. By using a symbolic link, you don’t need to make a copy of a file, so you save hard disk space and prevent inconsistencies caused by working with two copies of the same information. tar Command The tar command is an archive utility that lets you place a collection of many files (such as an entire subdirectory tree) into a single file, optionally compress- ing it at the same time. This provides a convenient way to save a copy of files, or to send a set of files to another user. The tar command is often used to un-archive (prepare for use) large collections of files that you download from the Internet. The rpm command, a software packag- ing tool described in Chapter 10, provides more functionality than tar for sending software packages to other users, but tar is widely used. Archives that have been created using tar will have a file extension of .tar or, if compressed, of .tgz. (The .tgz is a convention, not a rule.) To un-archive a tar file, use a command like this (add the z option if the archive is compressed) tar xvf archive.tar TCP/IP The primary networking protocol used by Linux, UNIX, and the entire Internet is called TCP/IP. When you configure your networking on OpenLinux, you provide network addresses that allow the TCP/IP protocols to function correctly. Other protocols such as HTTP (the Web) or SMTP (email) function on top of TCP/IP and depend on its correct functioning. Telnet Telnet is a method of accessing your Linux computer remotely that allows you to enter commands as if you were sitting at your Linux console. Telnet can be used via modem or Internet connection. Because telnet passes information unencrypted, be careful about using telnet to access your Linux system over the Internet. The standard telnet security set up by