3 Users and Groups

A user in Linux is represented by a user ID (UID), which is just an integer. Each user has a unique UID. A group in Linux is represented by a group ID (GID), which is also just an integer. Each group has a unique GID.

Each user is automatically a group in Linux. However, there are groups that do not correspond to a user. The difference between a user and a group (that does not correspond to a user) will be clear later on.