Check manual page of mem.used

mem.used

Author: Mathias Kettner

License: GPL

Distribution: official part of Check_MK

Supported Agents: Linux

This check measures the current usage of physical RAM and virtual memory used by processes. You can define a warning and critical level for the usage of virtual memory, not for the usage of RAM.

This is not a bug, its a feature. In fact it is the only way to do it right (at least for Linux): What parts of a process currently reside in physical RAM and what parts are swapped out is not related in a direct way with the current memory usage.

Linux tends to swap out parts of processes even if RAM is available. It does this in situations where disk buffers (are assumed to) speed up the overall performance more than keeping rarely used parts of processes in RAM.

For example after a complete backup of your system you might experiance that your swap usage has increased while you have more RAM free then before. That is because Linux has taken RAM from processes in order to increase disk buffers.

So when defining a level to check against, the only value that is not affected by such internals of memory management is the total amount of virtual memory used up by processes (not by disk buffers).

Check_mk lets you define levels in percentage of the physically installed RAM or as absolute values in MB. The default levels are at 150% and 200%. That means that this check gets critical if the memory used by processes is twice the size of your RAM.

Hint: If you want to monitor swapping, you probably better measure major pagefaults. Please look at the check kernel.

Item

None

Check parameters

Parameter	Type	Description
warning	int or float	the percentage of virtual memory used by processes at which WARNING state is triggered. If the level is defined as an integer value then it is interpreted as an absolute value in megabytes.
critical	int or float	the percentage or absolute value at which CRITICAL state is triggered

Performance data

Three variables are stored: the physical RAM, the used swap space and the sum of both. Maximum values for both variables are also transmitted, so that they can be visualized. All values are in Megabytes (1024 * 1024 bytes).

The template for PNP4Nagios that is shipped with check_mk stacks swap usage on top of RAM usage und thus shows the amount of virtual RAM that is used by processes.

If mem_extended_perfdata is set to True, then additional performance data is output (see below).

Inventory

mem.used creates one check on each host that provides the section <<>>. If that section also outputs information about the Windows page file, then the check <<>> is being used instead.

Configuration variables

Variable	Type	Description
memused_default_levels	float, float	Levels used by all checks that are created by inventory.
mem_extended_perfdata	boolean	If this variable is set to True, then the checks outputs additional performance data, if the agent provides that information. On Linux the amount of mapped and committed memory is output (see Mapped and Committed_AS in /proc/meminfo).

Examples

# Change default levels from 150%/200% to 100%/150%:
memused_default_levels = (100.0, 150.0)
checks = [
  # make explicit check for hosts with tag "oracle"
  ( ["oracle"], ALL_HOSTS, "mem.used", None, (80.0, 100.0) ),
  # use absolute levels at 8GB / 12GB for some other hosts
  ( ["host12","host34"], "mem.used", None, (8192, 12288) )
]