Security Concepts -User Accounts/Groups

User Accounts

Unique name
Unique ID
Password
File ownership is determined by user ID

Groups

Unique name
Unique ID
Users who need access to the same files

The security of a Linux system is based on a user being assigned a unique name, user ID
(UID) and password. When a user logs in, the UID is used to validate all requests for file
access.
When a file is created, the UID associated with the process that created the file is assigned
to the file. Only the owner or root can change the access permissions.
Users that require access to a set of files are placed in groups. A user can belong to
multiple groups. Each group has a unique name and Group ID (GID). Every user will
always be member of at least one group. This is called the primary group. In addition to
that, users may also be members of other groups. These are called secondary groups.