User Concept and User Groups
The Unix operating system is a multi-user operating system. Every real person who makes use of the system has a "user account" and a "user ID" defined on the system. The user ID is used for the authorization of the users (who is authorized for which transaction) and transaction records (who made what transaction when).Users log in to UNIX systems with their usernames and passwords. The operating system asks for the username and password of the user requesting the login, and compares these two entries with the user authentication system and confirms or rejects the user's login.
Each user has a user Number (user ID) assigned by the operating system. Any user's actions on the system are followed by this user number. During user identification, this number is automatically selected and assigned by the system if the system administrator does not specifically select a user number.
File, directory and device access controls are made with the user number. In UNIX context, there is a proprietor of all sorts of resources and ownership information is structured by user numbers.
"root" User
'Root' refers to the most authoritative user of the system and the owner of all the files.
The 'root' user owns all rights to the files and directories of the system. You should never be logged in as 'root' because it is not possible to recover from accidental changes. You must have root privileges by entering the password with the command su - (switch user) when necessary during operation.
The user number of the 'root' user is '0'. It is sufficient for the user number of that user to be changed to "0" in the /etc/passwd file so that a registered user on the system has the same rights as root. In this case, this user will have all rights over the system without using the 'su' command.
There are also a number of special users to run system services outside of root. The user shell of these users is defined as /sbin/nologin and it is not possible to access the system with username/password mapping.
User Groups
UNIX has user groups. UNIX users are members of these groups. Groups are treated as a group ID (gid) in UNIX in a manner similar to user identities in UNIX. Computer resources also have group access rights. It is possible to give a gratuity to the right of access to a resource on this account.The group ID of each user in the /etc/passwd file is the identity of the primary group that the user is a member of.
Users can also be a member of other groups from their main group. Other groups where the user is a member are kept in the /etc/group file.
Group information is kept in / etc / group file. Each line of the / etc / group file has the following format:
group_name:group_password:gid:user1,user2,user3
The last section in this line is given in the form of a list of members of the group "user1, user2, user3".
To read my previous article: Manual Pages and Communication Commands
