Because Debian is a multiuser system, it's designed to keep any one user or program from breaking the entire system. The kernel will not allow normal users to change important system files. This means that things stay the way they're supposed to, safe from accidents, viruses, and even malicious pranks. Unlike other operating systems, Debian is safe from these threats. You won't need an anti-virus program.
However, sometimes you need to change important system files; for example, you might want to install new software or configure your network connection. To do so, you have to have greater powers than a normal user; you must become the root user (also called the superuser).
To become root, just log on with the username root and the root password; this was set during installation, as described in section 3.15 on page .
At many sites, only the system administrator has the root password, and only the system administrator can do the things that one must be root to do. If you're using your own personal computer, you are the system administrator, of course. If you don't have root privileges, you will have to rely on your system administrator to perform any tasks that require root privileges.
Sometimes you'll have the root password even on a shared corporate or educational server, because the system administrator trusts you to use it properly. In that case, you'll be able to help administer the system and customize it for your needs. But you should be sure to use the password responsibly, respecting other users at all times.
If you have the password, try logging on as root now. Enter the whoami command to verify your identity. Then log out immediately. When you're root, the kernel will not protect you from yourself, because root has permission to do anything at all to the system. Don't experiment while you're root. In fact, don't do anything as root unless absolutely necessary. This isn't a matter of security, but rather of stability. Your system will run much better if it can keep you from making mistakes.
You may find the su command more convenient than logging in as root. su allows you to assume the identity of another user, usually root unless you specify someone else. (You can remember that su stands for Super User, though some say it stands for Set UserID.)
Here's something to try. Log on as yourself - that is, not as root. Then your session will look something like the one in Figure 4.1.
When you're doing system administration tasks, you should do as much as possible as yourself. Then use su, do the part that requires root privileges, and use the exit command to turn off privileges so you can no longer harm anything.
You can use su to assume the identity of any user on the system, not just root. To do this, type su user where user is the user you want to become. You'll have to know the user's password, of course, unless you're root at the time or the user has no password.