add netio doc page

docs/20_Checks/_index.md

@@ -26,7 +26,7 @@ There is one include script used by all checks:
 * [check_haproxy_status](check_haproxy_status.md)
 * [check_memory](check_memory.md)
 * [check_mysqlserver](check_mysqlserver.md)
-* check_netio
+* [check_netio](check_netio.md)
 * [check_netstat](check_netstat.md)
 * [check_onehost](check_onehost.md)
 * [check_onevm](check_onevm.md)

docs/20_Checks/check_netio.md

+# check_netio
+
+## Introduction
+
+Show network io for all or selected interfaces.
+
+This plugin scans `/proc/net/dev` with the regex `eth|en[ops][0-9]*` to show a few types of interfaces.
+
+### Requirements
+
+* none
+
+## Syntax
+
+```text
+> ./check_netio -h
+______________________________________________________________________
+
+CHECK_NETIO
+v1.1
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_netio.html
+______________________________________________________________________
+
+Show network io for all or selected interfaces.
+It shows the current counter value from /proc/net/dev and the speed 
+in byte per sec since last execution.
+
+This plugin sends performancedata.
+
+SYNTAX:
+  check_netio [-h] [-i INTERFACE(S)]
+
+OPTIONS:
+  -h               this help
+
+PARAMETERS:
+  -i  INTERFACE    show this interface only. Quote multiple interfaces.
+                   The check returns unknown if an interface does not
+                   exist.
+
+EXAMPLES:
+
+  check_netio      show netio of all network interfaces
+  check_netio -i "eth0 eth1" 
+                   show netio of given interfaces.
+
+```
+
+## Examples
+
+### Host with single interface
+
+A simple call on a host with a single interface... `check_netio` returns
+
+```txt
+OK: Network IO ... IN 0 MB/s >> [host] >> 0 MB/s OUT
+
+--- enp0s31f6:
+       receive:      1079156830      28849 byte/s     
+      transmit:      1082596810       2898 byte/s     
+
+ |rx=28849;; tx=2898;;
+ ```
+
+### Custom interface
+
+You get the same output with `check_netio -i enp0s31f6`.
+
+If you enter a wrong interface the check returns with "UNKNOWN".
+`check_netio -i "whatever"`returns
+
+```txt
+UNKNOWN: Network IO ... IN 0 MB/s >> [host] >> 0 MB/s OUT
+
+--- whatever:
+UNKNOWN: the interface whatever does not exist.
+
+ |rx=0;; tx=0;;
+ ```