Managing Users and Permissions in CentOS

Managing users and permissions is crucial for maintaining a secure and organised CentOS system. This tutorial will guide you through creating and deleting users, managing groups, and setting up permissions. We'll also cover basic use of "sudo" to grant administrative access.

1. Creating a New User

To create a new user, use the "useradd" command followed by the username. This command creates a new user account and home directory.



Then, set a password for the new user:


Replace "username" with your desired username.

2. Deleting a User

To delete a user and their home directory, use the "userdel" command with the "-r" option:

3. Managing Groups

• Creating a New Group: Use "groupadd" followed by the group name.
  sudo groupadd groupnameCopy
• Adding a User to a Group: Add a user to an existing group with the "usermod -aG" command.
  sudo usermod -aG groupname usernameCopy
• Listing User Groups: To see which groups a user belongs to, use the "groups" command.
  groups usernameCopy
• Removing a User from a Group: Remove a user from a group by editing "/etc/group" or by running the command:
  sudo gpasswd -d username groupnameCopy

4. File and Directory Permissions

In CentOS, permissions define who can read, write, or execute files and directories. To check permissions, use "ls -l" to list the contents of a directory:



Each file's permissions are shown in a string like "-rw-r--r--", where:

• The first character shows if it’s a file (-) or directory (d).
• The next three characters are owner permissions (read, write, execute).
• The following three are group permissions.
• The last three are others' permissions.

5. Changing Permissions with "chmod"

The "chmod" command changes file or directory permissions. For example, to grant the owner read, write, and execute permissions:



Common Permissions:

• "7" = read, write, execute
• "5" = read and execute
• "4" = read only

6. Changing Ownership with "chown"

To change a file’s owner or group, use "chown". For example, to set "username" as the owner and "groupname" as the group:

7. Using "sudo" for Administrative Access

Granting a user "sudo" privileges allows them to run commands with administrative rights. Add a user to the "wheel" group to grant "sudo" access:



To check which users have sudo privileges, open the sudoers file:

Conclusion

With these commands, you can create, delete, and manage users and groups in CentOS. Managing permissions and using "sudo" securely ensures that only authorized users have access to critical system functions.