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SSH Linux sensor returns free instead of available memory



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Hi Paessler team

We have several linux machines which we can access only via SSH. The SSH memory sensor (we have the German version and they are called "SSH Speicherinfo") returns free memory instead of available memory. Free is an (almost) useless metric, as it also considers cached stuff in memory as being non-free. Hence free memory will sooner or later be close to zero the longer a system runs and the more the linux kernel can cache useful stuff. The free metric therefore does not provide anything useful, apart from showing whether the system was running long enough to fill the memory with useful things to cache. The really interesting metric would be available memory. But I cannot find the appropriate SSH Sensor that would show me available memory. Did I just not find it? Can you help me find the appropriate sensor?

Sidenote: I don't know what the sensor title in English is, but the German one is "Verfügbarer Speicher" that translated would mean available memory. This makes it even more confusing, that it does not return available memory (but instead returns free memory).

linux memory ssh sshm

Created on Jan 3, 2018 7:13:00 PM by  Reto (1) 1

Last change on Jan 4, 2018 6:50:58 AM by  Luciano Lingnau [Paessler]

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The values displayed by the sensor are correct, but please mind that they only consider real free memory while not taking in account cached and buffered memory.

For alternate readings, please use the SNMP Library Sensor with the Basic Linux Library.

Another alternative is to deploy the SNMP Custom Sensor or SNMP Custom Advanced Sensor using one of the following OID's:

The total amount of swap space configured for this host1.
The amount of swap space currently unused or available1.
The total amount of real/physical memory installed on this host1.
The amount of real/physical memory currently unused or available1.
The total amount of memory free or available for use on this host1.
The total amount of real or virtual memory currently allocated for use as shared memory1.
The total amount of real or virtual memory currently allocated for use as memory buffers1.
The total amount of real or virtual memory currently allocated for use as cached memory1.

With both of the above mentioned sensor you should be able to get all memory related information.

Additionally, if you need to see values in Percent, set-up an Sensor Factory Sensor to perform the required mathematical operations on top of the results of the SNMP sensors.

Kind regards,
Stephan Linke, Tech Support Team

Created on Jan 4, 2018 12:22:08 PM by  Stephan Linke [Paessler Support]

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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.