banshee/linux-collection/linux/ssh/cpu

Processors of a Linux, by SSH

Returns the usage of each processor and of all of them, the share of time spent waiting for disks (iowait) and the time stolen by the hypervisor (steal), and the number of processors. Seven watches are offered, each one set on the probe.

Versions

Generic: /proc/stat is written by the kernel the same way on Alpine, Debian and Fedora, and grep without options is the same in BusyBox and GNU grep. A kernel older than 2.6.11, without the steal column, stops the collector misconfigured.

How it works

The collector runs grep ^cpu /proc/stat and reads the cpu line (the whole) and the cpuN lines (each logical processor): user, nice, system, idle, iowait, irq, softirq and steal times since boot.

Usage is 1 − (idle + iowait) / total over the interval, total being the sum of the eight times; iowait and steal are their own share of the total.
On the first run there is no interval yet: the run is skipped. So is a run where a counter went backwards (iowait may on some kernels).
Nothing is written on the target.

Prerequisites

an SSH account for monitoring, without write rights; reading /proc needs no privilege;
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

Name	Label	Unit	Per instance
`cpu-busy`	Overall processor usage	%	no
`iowait`	Waiting for disks	%	no
`steal`	Stolen by the hypervisor	%	no
`core-busy`	Processor usage	%	yes, per processor (`cpu0`, `cpu1`…)
`cores`	Number of processors	—	no

Watches

Name	Title	Kind	Defaults	Checked by default
`cpu-high`	Processor saturated	above a threshold, on `cpu-busy`	warning above 85 %, critical above 95 %, for 3 runs	yes
`iowait-high`	Waiting for disks	above a threshold, on `iowait`	warning above 20 %, for 5 min; no critical	yes
`steal-high`	Stolen by the hypervisor	above a threshold, on `steal`	warning above 10 %, for 5 min; no critical	yes
`core-hot`	A processor saturated	above a threshold, on `core-busy`	warning above 95 %, for 3 runs; no critical	no
`core-idle`	A processor underused	below a threshold, on `core-busy`	warning below 20 %; no critical	no
`core-neglected`	A processor left idle	deviates from the others, on `core-busy`	warning when a processor is more than 30 % below the median of the others; no critical	no
`core-count`	Unexpected number of processors	expected value, on `cores`	no expected value: it raises nothing until one is set on the probe	yes

Limits

Values arrive from the second run on; a probe whose interval is long averages over it.
The processors are the logical ones: on a processor with two threads per core, each thread is one processor.
steal is only meaningful on a virtual machine; it stays at 0 on bare metal.