ad doc page

docs/20_Checks/_index.md

@@ -49,6 +49,7 @@ There is one include script used by all checks:
 * check_ssl
 * check_ssl_certs
 * check_systemdservices
+* [check_systemdunit](check_systemdunit.md)
 * check_timesync
 * check_uptime
 * hello

docs/20_Checks/check_systemdunit.md

+# Check Systemd unit
+
+## Introduction
+
+This check shows the status of a systemd unit.
+
+A unit is everything listed by systemctl command - services, timers, targets, ...
+
+## Requirements
+
+* `systemctl` binary
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+CHECK_SYSTEMDUNIT
+v1.0
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_systemdunit.html
+______________________________________________________________________
+
+Check a unit using systemctl status.
+
+The status is unknown if the command systemctl is not found.
+The status is critical if the service does not exist or is not running.
+
+SYNTAX:
+  check_systemdunit [-h] UNIT
+
+OPTIONS:
+  -h     this help
+  UNIT   Name of a unit - see output of 'systemctl' 
+
+EXAMPLES:
+
+  check_systemdunit mysql.service
+         show status of service mysql
+
+```
+
+## Examples
+
+``$ ./check_systemdunit nginx`` returns
+
+```txt
+OK: ● nginx.service - A high performance web server and a reverse proxy server
+     Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; preset: disabled)
+     Active: active (running) since Tue 2023-09-05 08:04:45 CEST; 8h ago
+    Process: 577 ExecStart=/usr/bin/nginx -g pid /run/nginx.pid; error_log stderr; (code=exited, status=0/SUCCESS)
+   Main PID: 612 (nginx)
+      Tasks: 2 (limit: 18881)
+     Memory: 3.0M
+        CPU: 38ms
+     CGroup: /system.slice/nginx.service
+             ├─612 "nginx: master process /usr/bin/nginx -g pid /run/nginx.pid; error_log stderr;"
+             └─613 "nginx: worker process"
+...
+```
+
+If a service does not exist: ``./check_systemdunit justadummy`` returns
+
+```txt
+CRITICAL: Unit justadummy.service could not be found.
+```