need to make system-wide changes or manage other users. However, they
might want to be able to change settings specific to their accounts (for
instance, a desktop background). Depending on how much control the system
administrator (the root or super user) likes to wield, regular users might not
even be able to do that.
The super user grants privileges to regular users using file and directory
permissions (as covered in Chapter 10, “Command-Line Beginner’s Class”).
For example, if the super user does not want you to change your settings in
~/.profile (the ~ is a shell shortcut representing your /home directory),
then as root she can alter the permissions so that you may read from, but not
write to, that file.
CAUTION
Because of the potential for making a catastrophic error as the super user,
use your system as a regular user most of the time and use your super user
powers only temporarily to do specific administration tasks. This is easier
to remember in Ubuntu than in some other distros because the root account
is initially disabled, and you must manually choose to use sudo. If you
work on a multiuser system, consider this advice an absolute rule; if root
were to delete the wrong file or kill the wrong process, the results could be
disastrous for the system (and likely the business that owns and operates it).
On your home system, you can do as you please. Running as root makes
many things easier—but much less safe—and we still do not recommend
using it all the time. In any setting, the risks of running as root are
significant, and we cannot stress enough how important it is to be careful
when working as root.The third type of user is the system user. The system user is not a person but
rather an administrative account that the system uses during day-to-day
running of various services. For example, the system user named www-data
owns the Apache web server and all the associated files. Only that user and
root can have access to these files; no one else can access or make changes to
these files. System users do not have a home directory or password, nor do
they permit access to the system through a login prompt.
You can find a list of all the users on a system in the /etc/passwd file.
User IDs and Group IDs
A computer is, by its very nature, a number-oriented machine. It identifies
users and groups by numbers known as the user ID (UID) and group ID
(GID). The alphabetic names display on your screen just for ease of use.