What Are Users?

Anyone trying to access a UNIX system requires the correct login information, which is allocated by a system administrator. At login time, you are prompted to enter your login name, followed by your password; if this is correct, you will be allowed on the system. This process is carried out for a number of reasons, including the following:

• It ensures that the system remains secure by only allowing users that know a login name and corresponding password to access the system.

• It allows the administrator to determine who is logged on at any particular time and also how much time and/or space they are using.

• It allows users to be gathered together into groups and assigned permissions as required.

While we often think of a user as being an actual person, this doesn't have to be the case. For example, users are often defined to enable a task to be easily carried out, such as the shutdown user that can be used to power down the machine.