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Why do SSH Disk Free and SNMP Linux Disk Free show different values for my target Linux system?



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I installed the SNMP Disk Check sensor and it seems to work, but it returns values that are significantly different from what they really are. The SSH Disk check works fine, so it must be something with SNMP. Any thoughts as to what could be the problem?

available disk-free free prtg sensors snmp space ssh values

Created on Nov 5, 2012 10:34:12 AM by  Daniel Zobel [Product Manager]

Last change on May 6, 2019 11:17:25 AM by  Maike Guba [Paessler Support]

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This article applies to PRTG Network Monitor 19 or later

Disk free measurements via SNMP vs. SSH

The behavior is as expected.

Both the SSH Disk Free and SNMP Linux Disk Free sensors report correct values regarding their individual method of measurement:

  • The SSH sensor uses the df command and returns the free space of the volume, minus a reserve defined for this volume. So, this sensor shows the disk space that is actually available for use. Note: The size of the reserved disk space can be defined with tune2fs.
  • The SNMP sensor returns the free space (this means all disk space that is not yet used). But not all of this space may be available for use, as a part of this space can be reserved.

For more information, refer for example to Walker News: Why The Linux df Command Shows Lesser Free Disk Space?

Created on Nov 5, 2012 10:58:26 AM by  Daniel Zobel [Product Manager]

Last change on Dec 10, 2020 2:29:58 PM by  Brandy Greger [Paessler Support]

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