updated notes

src/rhcsa.md

@@ -582,4 +582,23 @@ pool 2.rhel.pool.ntp.org iburst # Add the RHEL time server
 
 sudo systemctl start chronyd # Start the chrony service
 sudo systemctl enable chronyd # Enable the chrony service to start on boot
+```
+
+## Secure Linux Systems
+
+### lsattr
+```bash
+lsattr # List the attributes of the files and directories
+
+lsattr /etc/passwd # List the attributes of the /etc/passwd file
+```
+
+### chattr
+```bash
+chattr +i /etc/passwd # Set the immutable attribute on the /etc/passwd file
+chattr -R +i /etc/ # Set the immutable attribute on the /etc/ directory and all its contents
+chattr +a /etc/passwd # Set the append only attribute on the /etc/passwd file
+
+chattr -i /etc/passwd # Remove the immutable attribute on the /etc/passwd file
+chattr -R -i /etc/ # Remove the immutable attribute on the /etc/ directory and all its contents
 ```