User Concept and User Groups

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
 

User Concept in UNIX and Linux

User Concept in UNIX and Linux

How to Choose a Username and Password

User names must be chosen to consist of the English alphabet letters (a-z, A-Z) and numbers (0-9). The letters used in other alphabets should not be used in user names; Those letters are not accepted by many Linux distributions and other UNIX variants.

It is preferred that the usernames are selected in a manner that will generally invoke the user's real name. Only names, only surnames or suffixes, are common username alternatives.

User passwords must be chosen so complex that they can not be easily guessed by anyone other than the user. Since the checking of the user identity is performed only on a password basis, the password must not be known by anyone other than the user himself or herself.

It is recommended that an active password be at least six letters long and consist of a combination of letters, numbers and punctuation marks. Since the password is based on confidentiality, it must not be stored in paper form or any electronic form.

User names and passwords are case sensitive. In this sense, "wwalter" and "WWalter" are perceived as two different user names.

Criteria for a Good Password 

A good password must be:

• at least 8 characters long
• too complex to predict
• simple enough to remember
• contain at least one case difference
• contain at least one digit (0-9)
• contain at least one punctuation mark
• not contain repetitive numbers or characters 

Periodically, you should change your password regularly. Many system users are forced to change their passwords every 3 months or 6 months (For example banks). 

User Definition File

Traditionally all UNIX settings are stored in text files, this tradition continues under Linux as well. Storing all settings in text files allows all settings to be made with text editors. Any programmer can easily make maintenance tasks by quickly creating programs to organize settings in text files.

 The basic user authentication information is kept in the file /etc/passwd. In this file, each row represents one user: User name, password, user id, group number, personal information (For example; name, surname or phone number), home directory and user shell.  

Example format:

•  username:password:user_id:group_id:additional_info:home_directory:shell

To improve security in modern UNIX variants, encrypted user passwords are kept in the /etc/shadow file, not in the /etc/passwd file. The passwords appear as "x" in the /etc/passwd file. The /etc/shadow file can only be read and written by the system administrator, in other words, "root".


To read my previous article: Free Software Philosophy GPL and BSD