banshee/linux-collection/linux/ssh/swap

Swap of a Linux, by SSH

Returns the size of the swap, what it holds, and the pages read back from it and written to it per second. Pages read back again and again say the memory is too small, far better than used swap, where the kernel readily stores pages nobody needs any more.

How it works

The collector runs cat /proc/meminfo /proc/vmstat and reads SwapTotal and SwapFree (in KiB) and the counters pswpin and pswpout (pages since boot).

The pages per second come from the counters over the interval between two runs: the first run is skipped, as is a run where a counter went backwards.
Portable: both files are written by the kernel the same way on Alpine, Debian and Fedora. Nothing is written on the target.

Prerequisites

an SSH account for monitoring, without write rights;
the fingerprint of the server's host key, set in protocol:ssh:fingerprint (not needed when the Security settings trust the first SSH fingerprint presented).

Outputs

Output	Unit	Meaning
`total`	MiB	swap size
`used`	MiB	swap in use
`used-percent`	%	share of swap in use
`swap-in`	pages/s	pages read back from swap
`swap-out`	pages/s	pages written to swap

Watches

Watch	Kind	Defaults	Checked
`used-percent` Swap saturated	above, on `used-percent`	warning 80, critical 95, for 3 runs	yes
`swapping` Sustained swapping	above, on `swap-in`	warning 100, for 5 min	yes

Limits

A machine without swap (SwapTotal at 0) stops the collector misconfigured: the probe has nothing to measure, and says so rather than show green.
A page is 4 KiB on most machines, 16 or 64 KiB on some ARM systems: swap-in and swap-out count pages, not bytes.