What are Users and Groups?
Users and Groups are Operating System concepts for managing access and permission to system resource, that can be employed for security and organization of an Operating System by restricting different user’s scope of action.
Users in Operating System-
A user is an individual or process that interacts with the operating system. Every user have a user account on the Operating System identified by a unique username and a user ID (UID). A user account stores information about the user such as Login Credentials, Home Directory, System Configurations, etc. User’s access to the resources is often associated with specific level of privileges and permissions which determines what operation they can perform and what resources they have access to.
There are different types of users classified on the basis how they are managed, whereas they are broadly classified into-
- Regular User- These are standard users who have limited access to system resources. They can typically only access their own files and programs.
- Super Users- Super Users have complete control over the system. Thus, they have privileges to access and modify all files, resources and configurations on the system. They are usually referred as Root User or Administrators. Because they can alter privileges of all users and groups on the system.
- System Users- These are typically special users created by the OS or applications for running system processes and services such as nobody or daemon.
Groups in Operating System-
Groups are collections of users who share the same permissions or privileges. They allow administrators to assign permissions to a group rather than to individual users. When users are added to a group, they inherit the group’s permissions. This simplifies the management of permissions for a large number of users. Like users, groups are also identified using Group ID.
There are primarily two types of groups-
- Primary Group- Each user has a primary group, which is the default group for the user and is often used for file ownership.
- Supplementary Groups- These are additional groups that a user may belong to. A user can be a member of multiple groups, and each group may have different access rights to files and resources.
Permissions or Access Control-
Permissions define what actions a user or group can perform on a file, directory, or resource. In an Operating System, the permissions granted to users or groups usually include operations such as-
- Read (r)- The ability to view or read the contents of a file or list the contents of a directory.
- Write (w)- The ability to modify the contents of a file or add/remove files within a directory.
- Execute (x)- The ability to run a file as a program or script. For directories, execute permission allows users to enter the directory and access its contents.
- Special Permissions- In some systems, there may be additional permissions, such as setuid, setgid, or sticky bits.
In Linux and UNIX like operating systems, the permissions are usually assigned to owner, group and other users.
- Owner Permission- It defines what operations the owner or creator of the file or directory can perform.
- Group Permission- It defines what operation the member of a group can perform on a file or directory.
- Other Permission- It defines what operations other users can perform on a file or directory.
Special Permissions-
Some operating systems support special types of permissions to give additional control over resources:
- Setuid (Set User ID)- When set on an executable file, this permission allows a user to run the file with the privileges of the file’s owner (usually root), regardless of who executes it.
- Setgid (Set Group ID)- When set on a file, this permission forces the file to run with the group permissions of the group associated with the file, not the group of the user running the file.
- Sticky Bit- Typically used on directories, this permission ensures that only the file owner or root can delete or rename files within the directory, even if other users have write access to the directory.
Why Use Users and Groups?
- Security- By separating users and defining different access levels, an Operating System can restrict access to sensitive data and system resources, reducing the risk of accidental or malicious misuse.
- Organization- Groups allow admins to categorize users based on their role in the organization (e.g., developers, managers, support staff) and assign appropriate permissions to each group.
- Efficiency- Instead of modifying permissions for each user individually, system administrators can adjust permissions for an entire group, simplifying system management.