Each user account on a computer system is identified by a user name (or login name) and user ID. Normally, each user name has a unique user ID, but it is possible for several login names to have the same user ID. The user names and corresponding user IDs are stored in a data base which you can access as described in section User Database.
Users are classified in groups. Each user name also belongs to one or more groups, and has one default group. Users who are members of the same group can share resources (such as files) that are not accessible to users who are not a member of that group. Each group has a group name and group ID. See section Group Database, for how to find information about a group ID or group name.
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