about: add doc pages

docs/20_Checks/_index.md

@@ -7,6 +7,7 @@ There is one include script used by all checks:
 
 ## Check scripts
 
+* [about](about.md)
 * [check_apache_requests](check_apache_requests.md)
 * [check_ceph_diskfree](check_ceph_diskfree.md)
 * [check_ceph_io](check_ceph_io.md)

docs/20_Checks/about.md

+# About
+
+## Introduction
+
+This check shows a short summary for the current system.
+Its status is always OK.
+
+## Requirements
+
+Nothing special.
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+ABOUT
+v1.2
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/about.html
+______________________________________________________________________
+
+About ... shows a short summary for the system:
+
+  * perating system
+  * cpu
+  * ram
+  * diskspace
+  * checked services
+
+SYNTAX:
+
+  about [-h]
+
+OPTIONS:
+
+  -h, --help 
+      this help
+
+```
+
+## Example
+
+```txt
+# ./about
+debian 12 / 16 cpu / 62.684 GB ram
+
+>>>>>>>>>> CPU: 16
+model name      : Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
+
+>>>>>>>>>> Memory
+RAM total    65729512 kB
+Swap         999420 kB
+
+>>>>>>>>>> Disks
+Filesystem                       Size  Used Avail Use% Mounted on
+/dev/mapper/icinga--01--vg-root  218G   28G  179G  14% /
+/dev/sda1                        455M  105M  326M  25% /boot
+
+>>>>>>>>>> Services
+Apache-httpd
+Carbon-Cache
+Cron
+Cronjob-watcher
+Icinga2
+Icinga-Director
+Mariadb
+PHP-FPM
+Postfix
+SSH
+```