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.
[Illustration: Figure 4.1: Sample session with su]
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.