Added cockpit cloud-init example

examples/cloud-init/cockpit.yaml

@@ -0,0 +1,31 @@
+#cloud-config
+
+# Use another port instead of the default 9090. Also, close port 9090 behind.
+#
+# Tested on:
+# - Oracle Linux 8.6
+
+# On cloud instances, remember to open the port in the NSG.
+
+bootcmd:
+  # `cloud-init` has issues with `firewall-cmd`, using the offline version.
+  - firewall-offline-cmd --add-port='48763/tcp' --zone='public'
+
+packages:
+  - cockpit
+
+write_files:
+  - path: /etc/systemd/system/cockpit.socket.d/listen.conf
+    content: |
+      [Socket]
+      ListenStream=
+      ListenStream=48763
+
+runcmd:
+  # Allow the new port in SELinux.
+  - semanage port -a -t 'websm_port_t' -p 'tcp' '48763'
+
+  # Apply the changes.
+  - systemctl reload 'firewalld.service'
+  - systemctl daemon-reload
+  - systemctl restart 'cockpit.socket'

knowledge base/nc.md

@@ -14,13 +14,26 @@
 
 ```sh
 # Check ports on hosts.
-nc -Nnvz 192.168.0.81 22
+nc -Nnvz 192.168.0.81 22-25
 nc -Nvz host.name 443
+nc -Nvz -u dns.server 123
 
 # List hosts with a specific port open.
+# But you might just want to use `nmap`.
 parallel -j 0 "nc -Nnvz -w 2 192.168.0.{} 22 2>&1" ::: {2..254} \
 | grep -v "timed out"
 
 # Wait for a host to be up.
 until nc -Nvz -w 3 pi.lan 22; do sleep 3; done
+
+# Listen mode.
+nc -l 5666
 ```
+
+## Sources
+
+- [How To use Netcat to establish and test TCP and UDP connections]
+
+<!-- project's references -->
+
+[how to use netcat to establish and test tcp and udp connections]: https://www.digitalocean.com/community/tutorials/how-to-use-netcat-to-establish-and-test-tcp-and-udp-connections