check_memory: add doc page

check_memory

@@ -54,6 +54,8 @@ Check memory usage incl. free, used and total memory.
 On higher memory usage the process table with top 5 top consumers will 
 be shown.
 
+This plugin sends performancedata.
+
 SYNTAX:
 $(basename $0) [-w WARN_LIMIT] [-c CRITICAL_LIMIT] [-s SWAP_LIMIT] [-p PROCESS_LIMIT] [-h]
 

docs/20_Checks/_index.md

@@ -24,7 +24,7 @@ There is one include script used by all checks:
 * [check_fs_writable](check_fs_writable.md)
 * [check_haproxy_health](check_haproxy_health.md)
 * [check_haproxy_status](check_haproxy_status.md)
-* check_memory
+* [check_memory](check_memory.md)
 * check_mysqlserver
 * check_netio
 * [check_netstat](check_netstat.md)

docs/20_Checks/check_memory.md

+# Check Memory (RAM)
+
+## Introduction
+
+**check_memory** Check memory usage incl. free, used and total memory.
+It reads /proc/meminfo and fetches the needed values.
+
+* MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code)
+* MemFree: Is sum of LowFree+HighFree (overall stat)
+* MemAvailable: delta of total - free
+* Buffers: Memory in buffer cache. mostly useless as metric nowadays Relatively temporary storage for raw disk blocks shouldn’t get tremendously large
+* Cached: Memory in the pagecache (diskcache) minus SwapCache, Doesn’t include SwapCached
+* SwapCached:  Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn’t need to be swapped out AGAIN because it is already in the swapfile. This saves I/O )
+* SwapTotal: Total amount of physical swap memory.
+* SwapFree: Total amount of swap memory free. Memory which has been evicted from RAM, and is temporarily on the disk
+* Slab: in-kernel data structures cache
+* SReclaimable: reclaimable parts of Slab, e.g., caches
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+CHECK_MEMORY
+v1.9
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_memory.html
+______________________________________________________________________
+
+Check memory usage incl. free, used and total memory.
+On higher memory usage the process table with top 5 top consumers will 
+be shown.
+
+This plugin sends performancedata.
+
+SYNTAX:
+check_memory [-w WARN_LIMIT] [-c CRITICAL_LIMIT] [-s SWAP_LIMIT] [-p PROCESS_LIMIT] [-h]
+
+OPTIONS:
+    -w VALUE   Warning level for RAM usage [%]; default: 75
+    -c VALUE   Critical level for RAM usage; default: 90
+
+    -s VALUE   Critical level for SWAP usage; default: 50
+    -p VALUE   show process info with highest memory consumption if 
+               usage is > NN %; default: 50
+
+    -h or --help   show this help.
+
+PARAMETERS:
+
+    none
+
+EXAMPLE:
+check_memory -w 90 -c 95 -p 70
+
+```
+
+### Requirements
+
+* bc
+
+## Examples
+
+`$ check_memory -w 90 -c 95 -p 70` returns
+
+```txt
+OK: RAM usage 46 % of 7955 MB (machine has no Swap)
+
+MemTotal:        8146916 kB
+MemFree:          901724 kB
+MemAvailable:    4328748 kB
+Buffers:          117988 kB
+Cached:          3045292 kB
+SwapCached:            0 kB
+SwapTotal:             0 kB
+SwapFree:              0 kB
+Slab:             682424 kB
+SReclaimable:     591596 kB
+ |memory-total=7955MB;;;0;7955 memory-used=3729MB;;;0;7955 memory-avail=4226MB;;;0;7955 memory-free=880MB;;;0;7955 memory-buffers=115MB;;;0;7955 memory-cached=2973MB;;;0;7955 memory-sreclaim=577MB;;;0;7955
+```