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docs/20_Checks/check_conn.md

+## Check TCP or UDP connection
+
+Script: `check_conn`
+
+It is a plugin to check oe or mmultiple tcp and udp connections to localhost or a remote system.
+
+## Standalone installation
+
+From this repository ypu need next to this script:
+
+* `inc_pluginfunctions` shared function for all IML checks written in bash
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+CHECK_CONN
+v1.2
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_conn.html
+______________________________________________________________________
+
+SYNTAX:
+check_conn OPTIONS
+
+You can create a file named ./check_conn.cfg
+and add your connections there. 
+To start you can copy the file ./check_conn.cfg.dist
+
+OPTIONS:
+
+    -h or --help   show this help.
+    -t CONNECTION  test given connection; This param ignores entries
+                   in the config file. For multiple connection tests
+                   quote the parameter value and set spaces between
+                   the connections.
+
+PARAMETERS:
+
+    CONNECTION     Connection in the same syntax like in the config:
+                   tcp/host/port
+                   udp/host/port
+EXAMPLES:
+
+check_conn         If no param is given it checks entries in ./check_conn.cfg
+
+check_conn -t "tcp/api.example.com/443"
+                   Check a single connection
+
+check_conn -t "tcp/api.example.com/443 tcp/localhost/3306"
+                   Check multiple connections.
+
+
+```
+
+## Examples
+
+Check a single tcp port which is currently open:
+
+```txt
+./check_conn -t "tcp/localhost/80"
+OK: tcp check - 1 checks - 1 OK; 0 warnings; 0 errors 
+tcp/localhost/80 OK
+```
+
+Check multiple connections - one port is open the other closed:
+
+```txt
+./check_conn -t "tcp/localhost/22 tcp/localhost/443"
+CRITICAL: tcp check - 2 checks - 1 OK; 0 warnings; 1 errors 
+tcp/localhost/22 FAILED
+tcp/localhost/443 OK
+```