BCE-C712 Linux System Administration

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Managing User Accounts

Groups and the Group File

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n Unix-like operating systems, groups are used to organize and manage users with similar privileges or access rights. Each user on a Unix system belongs to one or more groups. Groups are defined in the group file, often located at /etc/group.

Here’s an overview of the group file entry:

group_name:password:GID:user_list
  1. group_name: This field contains the name of the group.
  2. password: Historically, this field used to store an encrypted password for the group. However, in modern Unix systems, it is typically left empty or contains a placeholder.
  3. GID (Group ID): This is a unique numerical identifier assigned to each group. It is used to differentiate between groups with similar names.
  4. user_list: This field contains a comma-separated list of usernames that are members of the group.

Example entry in the group file:

developers:x:1001:jane,john,mark
  • Group Name: developers
  • Password: (hashed or placeholder)
  • GID: 1001
  • User List: jane, john, mark

Groups serve several purposes in Unix-like systems:

  1. Access Control:
    • Groups are used to define access permissions to files and directories. By assigning files to specific groups, you can control which users have access to them.
  2. Resource Sharing:
    • Groups allow multiple users to share files and resources while maintaining control over who can access them.
  3. Privilege Separation:
    • By categorizing users into different groups, you can assign specific privileges or restrictions to different sets of users.
  4. System Administration:
    • Groups are used to grant administrative privileges to specific users, allowing them to perform tasks that require elevated permissions.
  5. Process Control:
    • Groups can be used in conjunction with tools like sudo to allow certain users to execute commands with elevated privileges.
  6. Security:
    • Groups play a role in implementing the principle of least privilege, ensuring that users have the minimum level of access required to perform their tasks.

It’s important to note that the group file is typically readable by all users on the system, but only writable by the superuser (root) or users with appropriate administrative privileges. The actual group information is stored in the file, but it is also maintained in the system’s memory for faster access.