User and group permissions – User and Group Administration – Linux operating system

User and group permissions play a vital role in controlling access to files, directories, and system resources in Linux. By assigning appropriate permissions to users and groups, you can ensure that only authorized users can read, write, or execute specific files or perform certain operations. Here’s an overview of user and group permissions in Linux:

1. Permission Types:
   • There are three types of permissions: read (r), write (w), and execute (x).
   • Read permission (r) allows viewing the contents of a file or directory.
   • Write permission (w) allows modifying or deleting a file or directory.
   • Execute permission (x) allows executing a file or accessing a directory.
2. Permission Levels:
   • Permissions are assigned at three levels: user, group, and others.
   • User-level permissions apply to the owner of the file or directory.
   • Group-level permissions apply to the group associated with the file or directory.
   • Others-level permissions apply to all users who are not the owner or in the group.
3. Viewing Permissions:
   • You can view the permissions of a file or directory using the ls -l command.
   • The output displays the permissions in the form of ten characters, representing user, group, and others permissions, respectively.
4. Modifying Permissions:
   • The chmod command is used to modify permissions.
   • The command can be used with either symbolic or numeric notation.
   • Symbolic Notation:
     • The symbolic notation uses symbols (+, -, =) along with the permission type (r, w, x) and the permission level (u, g, o, a).
     • Example: chmod u+x myfile (adds execute permission for the owner of the file)
     • Example: chmod g-w myfile (removes write permission for the group)
     • Example: chmod o=r myfile (sets read-only permission for others)
   • Numeric Notation:
     • The numeric notation uses three digits to represent permission bits: user, group, and others.
     • Each permission type (r, w, x) is assigned a value: read (4), write (2), execute (1).
     • Example: chmod 755 myfile (gives read, write, and execute permissions to the owner, and read and execute permissions to the group and others)
5. Changing Ownership:
   • The chown command is used to change the ownership of a file or directory.
   • Example: sudo chown newowner myfile (changes the owner of the file to “newowner”)
   • The chown command can also change the group ownership using the : separator: sudo chown owner:newgroup myfile
6. Changing Group Ownership:
   • The chgrp command is used to change the group ownership of a file or directory.
   • Example: sudo chgrp newgroup myfile (changes the group ownership of the file to “newgroup”)

Properly managing user and group permissions is crucial for maintaining data security and access control in Linux. By assigning appropriate permissions, you can ensure that users and groups have the necessary access rights to perform their tasks while preventing unauthorized access or modifications to sensitive files and directories.