Free space on / reports wrong data

[Abraxas]

Hi,
I have a Debian server with nxagent on it. There was a trace running that filled the / partition to 100%.
NetXMS was configured to trigger the most important alarm at 1% free space, but it never triggered. When I checked the logged data, the agent never reported the free percentage below 5%, as in the attached graph.
After freeing up space (it has not about 78% free space), nxagent reports it ok. Any idea what can cause this and how to fix it?

And I also have a second issue with this: I actually have 2 data collection items for root disk space, and on the other one, there were 3 thresholds: 16%, 10% and 8%. The 16% threshold was reached and got triggered, but the other 2 did not, even though the free space % went a bit below 5% (instead of 0, as mentioned above).

Thank you,
Alex

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[Filipp Sudanov]

For 5% - could it be that EXT3 file system reserves about 5% of space for it's needs and actually does not allow to write files if it comes to that limit? E.g. some info here: https://linuxaria.com/pills/free-reserved-ext3-ext4-filesystems

About 16% threshold - thresholds are processed from top to bottom. If "process all thresholds" is unchecked, which is the default, thresholds are processes only until first one triggers. So if you have e.g. 4% value it will trigger 16% threshold and won't go any further. So the 16% should go to the bottom of the list.

[Abraxas]

Thank you Filipp!
Wow, I can't believe this is the first time I see the "Process all thresholds" checkbox, and of course, it was unchecked. Time to review all monitored parameters with multiple thresholds.

Regarding the reservation, I was aware the OS has a reserved limit, but I always believed that's why I always see a bit less available space than df shows.