Check memory-usage

Overview

Monitors physical memory utilization with threshold-based alerting on overall memory usage percentage. Reports total, used, available, and free memory, plus platform-specific metrics (shared, buffers, cached).

Alerting Logic:

  • Thresholds apply to overall memory usage percentage (default: WARN at 90%, CRIT at 95%)

  • Single-point evaluation - alerts immediately when threshold exceeded (no sustained load detection)

  • Uses psutil’s percent calculation which accounts for platform-specific memory semantics

Data Collection:

  • Physical memory statistics only (RAM, excludes swap)

  • Reports available metric for cross-platform usable memory estimation

  • Platform-specific metrics on Linux/BSD: shared, buffers, cached

  • Optional top-N memory-consuming processes by RSS (--top, default: 5), aggregated by process name

Compatibility:

  • Cross-platform: Linux, Windows, *BSD, macOS

  • Stateless check - no database or state persistence required

Important Notes:

  • Memory usage calculations differ between tools (top, htop, free) due to different counting methods and kernel versions

  • This check uses psutil’s cross-platform available metric for consistency

  • Process memory percentages may sum to >100% on Linux due to shared memory accounting

Fact Sheet

Fact

Value

Check Plugin Download

https://github.com/Linuxfabrik/monitoring-plugins/tree/main/check-plugins/memory-usage

Check Interval Recommendation

Once a minute

Can be called without parameters

Yes

Compiled for Windows

Yes

3rd Party Python modules

psutil

Help

usage: memory-usage [-h] [-V] [--always-ok] [-c CRIT] [--top TOP] [-w WARN]

Displays system memory usage and alerts on sustained high usage. Reports
total/used/available/free plus shared/buffers/cached, and evaluates WARN/CRIT
against the overall usage percentage. Perfdata is emitted for all fields so
you can graph trends over time. With `--top`, the most memory-consuming
processes are listed (by RSS and percentage) to aid quick diagnosis. Cross-
platform on all psutil-supported systems (Linux, Windows, *BSD, macOS).

options:
  -h, --help           show this help message and exit
  -V, --version        show program's version number and exit
  --always-ok          Always returns OK.
  -c, --critical CRIT  Set the critical threshold for memory usage (in
                       percent). Default: 95
  --top TOP            List x "Top most memory consuming processes". Use
                       `--top=0` to disable this feature. Default: 5
  -w, --warning WARN   Set the warning threshold for memory usage (in
                       percent). Default: 90

Usage Examples

./memory-usage
./memory-usage --warning=90 --critical=95 --top=5

Output:

36.2% - total: 3.8GiB, used: 1.1GiB, available: 2.4GiB, free: 989.4MiB
shared: 41.6MiB, buffers: 3.6MiB, cached: 1.8GiB

Top 5 most memory consuming processes:
1. php-fpm: 810.7MiB (20.7%)
2. forkit: 418.3MiB (10.7%)
3. kit_spare_001: 335.5MiB (8.6%)
4. mariadbd: 306.2MiB (7.8%)
5. icinga2: 63.8MiB (1.6%)

States

  • WARN or CRIT if total memory usage is above a given threshold.

Perfdata / Metrics

Name

Type

Description

available

Bytes

The memory that can be given instantly to processes without the system going into swap. This is calculated by summing different memory values depending on the platform and it is supposed to be used to monitor actual memory usage in a cross platform fashion.

buffers

Bytes

Cache for things like file system metadata (Linux, BSD).

cached

Bytes

Cache for various things (Linux, BSD).

free

Bytes

Memory not being used at all (zeroed) that is readily available; note that this doesn’t reflect the actual memory available (use available instead). total - used does not necessarily match free.

shared

Bytes

Memory that may be simultaneously accessed by multiple processes (Linux, BSD).

total

Bytes

Total physical memory (exclusive swap).

usage_percent

Percentage

used

Bytes

Memory used, calculated differently depending on the platform and designed for informational purposes only. total - free does not necessarily match used.

Troubleshooting

This checks sometimes reports > 100% memory usage on Linux
That’s fine, the RES column in top says the same if you sum up all values for a process (attention: the values in top’s RES column are KB by default), and compare process memory to total physical system memory. If machine does not swap, this is kind of Linux memory management mystery.

Credits, License