Chapter 12. Users and Groups

Linux is a multiuser operating system, meaning that one or more users can work on it at the same time. Each user is referenced by a user name. Each user name has a user ID or UID associated with it and one or more groups. Like user names, group names are also represented by a numeric identifier, this time called a group ID or GID. A user's UID is as unique as a group's GID.

When it comes to your files and directories, security on a Linux system is defined by means of permissions, which directly relate to the user ID. Users are either administrative users or regular users. The chief administrative user is called root. A user's ID is used to decide which commands can be executed and which files can be read from or written ...

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