إدارة المستخدمين والمجموعات - الفصل 6

Introduction to Operating Systems (SYST1)

• This course is part of the National School of Cybersecurity's (NSCS) 1st Year Basic Training in Cyber Security (1BT) program for 2024/2025.
• It's taught by Dr. Sassi Bentrad.
• The course covers Users, Groups and Permissions Management (10%).

Chapter 6: Users, Groups, and Permissions Management

• Linux is a multi-user operating system, meaning multiple users can use the computer simultaneously.
• Access permissions are needed for directories and files.
• Linux uses three access permissions for files and directories:
  • Owner (User)
  • Group
  • Other
• Permissions are represented:
  • read (r)
  • write (w)
  • execute (x)
• Absence of permission is denoted by a hyphen (-).
• Permissions can be viewed using numerical or symbolic notations.
• Different commands are used to manage users, groups, and permissions.

Owner Status

• There are three owner statuses:
  • Owner: The user who created the file/directory.
  • Owner Group: The primary group of the owner.
  • Others: Users not in the owner group.
• Commands like chown, chgrp, and chmod are used to manage owners, groups & permissions.

Permission (Access Mode)

• Permissions depend on the owner status.
• The ls -l command with the -l option displays permission information for files and directories.
• Permissions can be expressed numerically (octal) or symbolically.

Meaning of File Permissions

• Files are used to store data.
• r (Read): View the contents.
• w (Write): Change the contents.
• x (Execute): Run the program or instructions for binary files.

Meaning of Directory Permissions

• Directories are used to store files and directories.
• r (Read): View the directory contents (files and subdirectories).
• w (Write): Add, delete, or rename files within the directory
• x (Execute): enter the directory.

Superuser (Root User) vs. Normal User

• The superuser (root) has access to all system resources.
• Normal users have limited access based on permission settings.
• sudo is used to run commands with superuser privileges.
• Different accounts (e.g., user_a, user_b) with varying permissions are part of a system.

sudo Command (Run Command with Superuser Privileges)

• The sudo command allows normal users to run commands with superuser privileges.
• sudoers are users with the necessary permissions to use sudo.

su (Switch User) Command

• The su command is used to temporarily switch to another user, including the superuser (root).

useradd (Add User) Command

• Used to create new user accounts.
• Option -m automatically creates a home directory.

passwd (Set Password) Command

• Used to set up or change a user's password.

userdel (Delete User) Command

• Used to delete existing user accounts.
• Option -r also deletes the user's home directory.

Primary Group and Secondary Group

• Linux uses primary & secondary groups to manage user permissions.
• Primary group: the default group a user belongs to.
• Secondary group: additional group memberships for specified permissions
• Commands like groupadd, usermod, and gpasswd manage these groups.

groupadd (Add Group) Command

• Used to create new user groups.

usermod (Modify User Account Information)

• Used to modify a user's profile (including primary group, secondary groups, etc.) .

gpasswd (Add and Delete Users to Group) Command

• Used to add or remove users from groups.
• Supports password management for groups.

groupdel (Delete Group) Command

• Used to delete a group profile from the system.

chown (Change Owner of File and Directory) Command

• Used to change the ownership of files or directories.

chgrp (Change Group of File and Directory) Command

• Used to change the group ownership of files or directories

chmod (Change Access Mode) Command

• Used to modify the access permissions of files and directories.
• Symbolic and numerical methods are supported.

Check Current User Login Status (who and w command)

• Used for showing who's currently logged in and what they are doing.

id and groups (Check User ID and Group) Commands

• Used for checking the user ID and list of groups.

getent (Display User and Group Data) Command

• Retrieves data from system databases on users and groups.

chmod Command with Numbers

• Used to set permissions using numerical representations.
• The command uses octal numbers (base-8) representing permissions.

Extended access permissions

• Allows controlling access beyond basic rwx permissions.
• Used for granular sharing control.
• SUID & SGID bits affect how programs are executed and permission control.
• Sticky bit is used in directories to restrict file renaming & deletion.