The name "UNIX" may be familiar to some of you. You may even use a UNIX system at work, in which case this chapter may not be very interesting to you.
For those of you who never used it, reading this chapter is absolutely necessary. Knowing the concepts which will be introduced here answers a surprisingly high amount of questions commonly asked by beginners in the GNU/Linux world. Similarly, some of these concepts will likely answer most of the problems you may encounter in the future.
The users and groups concepts are extremely important, for they have a direct influence on all other concepts this chapter will introduce.
Linux is a true multiuser system, and in order to use your GNU/Linux machine, you must have an account on the said machine. When you created a user during the installation, you actually created a user account. You were prompted for the following items:
the "real name" of the user (whatever you want, in fact);
a login name;
a password (you did enter one, didn't you?).
The two important parameters here are the login name (commonly abbreviated to login) and password. In order to access the system, you absolutely need these.
When you create a user, a default group is also generated . As we will see later, groups are useful when you have to share files between several people. A group may contain as many users as you wish, and it is very common to see such a separation in large systems. For example, in a university, you could have one group per department, another group for teachers, and so on. The opposite is also true: a user can be a member of one or more groups, with a maximum of thirty-two. A math teacher, for example, can be a member of the teachers' group and also in his beloved math students' group.
All this does not tell you how to log in, however. So, here it comes.
If you chose to use the graphical interface upon boot-up, your startup screen will look similar to figure 1-1.
In order to login, you must enter your login name into the
text field, then enter your password into the password field. Note that you must type your password blindly; there will be no echo into the text field.If you are in console mode, your screen will look similar to figure 1-2.
You will then have to enter your login name at the
prompt and press Enter, after which the login program (called, what a surprise, login) will display a prompt, where you will enter the password for this account. Because the console login does not echo characters that represent the password, be careful when typing in your password... blindly.Note that you can login several times with the same account on additional consoles and under X. Each session you open is independent from others, and it is even possible to have several X sessions opened concurrently. By default, Mandrake Linux has six virtual consoles in addition to the one reserved for the graphical interface. You can switch to any of them by typing the key sequence Alt-F<n>, where <n> is the number of the console which you want to switch to. By default, the graphical interface is on console number 7.
During the installation, DrakX also prompted you for the password of a very special user: root. root is the system administrator, which will most likely be you. For your system's security, it is very important that the root account always be protected with a good password!
If you regularly login as root, it is very easy to make a mistake which can render your system unusable; one single mistake can do it. In particular, if you have not set a password for the root account, then any user can alter any part of your system (even other operating systems on your machine!). This is obviously not a very good idea.
It is worth mentioning that, internally, the system does not identify you with your login name but with a unique number assigned to this login name: the User ID (UID for short). Similarly, every group is identified by its Group ID (GID) and not its name.