Tuesday, August 21, 2007
by AidZ
Accessing a Unix SystemThere are many ways that you can access a Unix system. If you want the fullest possible access to the computer's commands and utilities, you must initiate a login session. The main mode of initiating a login session to a Unix machine is through a terminal, which usually includes a keyboard, and a video monitor. When a terminal establishes a connection to the Unix system, the Unix kernel runs a process called a tty to accept input from the terminal, and send output to the terminal. When the tty process is created, it must be told the capabilities of the terminal, so it can correctly read from, and write to, the terminal. If the tty process receives incorrect information about the terminal type, unexpected results can occur.
ConsoleEvery Unix system has a main console that is connected directly to the machine. The console is a special type of terminal that is recognized when the system is started. Some Unix system operations must be performed at the console. Typically, the console is only accessible by the system operators, and administrators.
Dumb terminalsSome terminals are referred to as "dumb" terminals because they have only the minimum amount of power required to send characters as input to the Unix system, and receive characters as output from the Unix system. Personal computers are often used to emulate dumb terminals, so that they can be connected to a Unix system. Dumb terminals can be connected directly to a Unix machine, or may be connected remotely, through a modem, a terminal server, or other network connection.
Smart terminalsSmart terminals, like the X terminal, can interact with the Unix system at a higher level. Smart terminals have enough on-board memory and processing power to support graphical interfaces. The interaction between a smart terminal and a Unix system can go beyond simple characters to include icons, windows, menus, and mouse actions.
Network-based access modesUnix computers were designed early in their history to be network-aware. The fact that Unix computers were prevalent in academic and research environments led to their broad use in the implementation of the Department of Defense's Advanced Research Projects Administration (DARPA) computer network. The DARPA network laid the foundations for the Internet.
FTPThe FTP (File Transfer Protocol) provides a simple means of transferring files to and from a Unix computer. FTP access to a Unix machine may be authenticated by means of a username and password pair, or may be anonymous. An FTP session provides the user with a limited set of commands with which to manipulate and transfer files.
TelnetTelnet is a means by which one can initiate a Unix shell login across the Internet. The normal login procedure takes place when the telnet session is initiated.
HTTPThe HTTP protocol has become important in recent years, because it is the primary way in which the documents that constitute the World Wide Web are served. HTTP servers are most often publicly accessible. In some cases, access to documents provided by HTTP servers will require some form of authentication.
Logging In and Logging Out
To ensure security and organization on a system with many users, Unix machines employ a system of user accounts. The user accounting features of Unix provide a basis for analysis and control of system resources, preventing any user from taking up more than his or her share, and preventing unauthorized people from accessing the system. Every user of a Unix system must get permission by some access control mechanism.
Logging in
Logging in to a Unix system requires two pieces of information: A username, and a password. When you sit down for a Unix session, you are given a login prompt that looks like this:
login:Type your username at the login prompt, and press the return key. The system will then ask you for your password. When you type your password, the screen will not display what you type.
Your usernameYour username is assigned by the person who creates your account. At ISU, the standard username is the first four letters of your last name concatenated with the first four letters of your first name. Your username must be unique on the system where your account exists since it is the means by which you are identified on the system.
Your password
When your account is created, a password is assigned. The first thing you should do is change your password, using the passwd utility. To change your password, type the command
passwd:
after you have logged in. The system will ask for your old password, to prevent someone else from sneaking up, and changing your password. Then it will ask for your new password. You will be asked to confirm your new password, to make sure that you didn't mistype. It is very important that you choose a good password, so that someone else cannot guess it. Here are some rules for selecting a good password.
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Publisher: Wiley
