adds telnet example to munin

modules/qualifying/learning_centralized_system_monitoring.md

@@ -203,6 +203,36 @@ munin-node-configure --shell --families=contrib,auto | sh -x
 Because the munin server client model is so basic you can find node software for most operating systems.
 I've run it successfully on [freeNAS](https://www.truenas.com/community/threads/install-munin-node.79224/#post-549934) but you can try a [windows](https://github.com/munin-monitoring/munin-node-win32) node as well.
 
+When I say *simple* I mean *really simple*.
+For those who like digging a bit deeper, you can connect to the munin node over telnet.
+From a terminal on the master, or any IP address that is in the allow list of the node, you can do the following.
+
+```
+waldek@muninserver:~$ telnet 10.8.0.1 4949
+Trying 10.8.0.1...
+Connected to 10.8.0.1.
+Escape character is '^]'.
+# munin node at vps-42975ad1.vps.ovh.net
+help
+# Unknown command. Try cap, list, nodes, config, fetch, version or quit
+list
+cpu df df_inode entropy fail2ban forks fw_conntrack fw_forwarded_local fw_packets if_err_eth0 if_err_tun0 if_eth0 if_tun0 interrupts irqstats load memory netstat ntp_kernel_err ntp_kernel_pll_freq ntp_kernel_pll_off ntp_offset open_files open_inodes proc_pri processes swap systemd-status threads uptime users vmstat
+fetch cpu
+user.value 21547781
+nice.value 22016
+system.value 8773929
+idle.value 895574842
+iowait.value 449848
+irq.value 0
+softirq.value 773399
+steal.value 540782
+guest.value 0
+.
+quit
+Connection closed by foreign host.
+waldek@muninserver:~$ 
+```
+
 ## Alternatives
 
 There are quite a few alternatives out there to choose from.