memory_bsd.go has a sysctl which isn't available in recent DragonflyBSD (not sure about previous one)

[iori-yja]

Summary

This error shown below is due to vm.swap_total sysctl that isn't available in recent DragonflyBSD (I am not sure about prior one, but FreeBSD has). I have changed the code as following patch which makes it works:

iori@tech-y09-dfly% git diff
diff --git a/collector/memory_bsd.go b/collector/memory_bsd.go
index 8c7265e..268dccc 100644
--- a/collector/memory_bsd.go
+++ b/collector/memory_bsd.go
@@ -98,7 +98,7 @@ func NewMemoryCollector() (Collector, error) {
                        {
                                name:        "swap_size_bytes",
                                description: "Total swap memory size",
-                               mib:         "vm.swap_total",
+                               mib:         "vm.swap_size",
                                dataType:    bsdSysctlTypeUint64,
                        },
                        // Descriptions via: top(1)

My question is that whether should I make PR to diverge Dfly's memory.go from memory_bsd.go. If this is applicable for other version of DragonflyBSD, I think it is worth to make them separate. If it is only seen in recent version of Dfly, I am not sure what to handle this difference. Please give me some hints to make a PR without regression.

Host operating system: output of uname -a

DragonFly tech-y09-dfly 5.3-DEVELOPMENT DragonFly v5.3.0.18494.gc70d4-DEVELOPMENT #1: Fri Aug 24 12:27:12 JST 2018 root@tech-y09-dfly:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

node_exporter version: output of node_exporter --version

Installed from source.
iori@tech-y09-dfly% git log | head -n 3
commit 7519967
Author: Ben Kochie superq@gmail.com
Date: Sat Oct 20 08:21:51 2018 +0200
iori@tech-y09-dfly% node_exporter --version
node_exporter, version (branch: , revision: )
build user:
build date:
go version: go1.10.3

node_exporter command line flags

node_exporter (default)

Are you running node_exporter in Docker?

No

What did you do that produced an error?

Wait for a couple of seconds.

What did you expect to see?

No errors

What did you see instead?

iori@tech-y09-dfly% node_exporter
INFO[0000] Starting node_exporter (version=, branch=, revision=)  source="node_exporter.go:82"
INFO[0000] Build context (go=go1.10.3, user=, date=)     source="node_exporter.go:83"
INFO[0000] Enabled collectors:                           source="node_exporter.go:90"
INFO[0000]  - boottime                                   source="node_exporter.go:97"
INFO[0000]  - cpu                                        source="node_exporter.go:97"
INFO[0000]  - exec                                       source="node_exporter.go:97"
INFO[0000]  - filesystem                                 source="node_exporter.go:97"
INFO[0000]  - loadavg                                    source="node_exporter.go:97"
INFO[0000]  - meminfo                                    source="node_exporter.go:97"
INFO[0000]  - netdev                                     source="node_exporter.go:97"
INFO[0000]  - textfile                                   source="node_exporter.go:97"
INFO[0000]  - time                                       source="node_exporter.go:97"
INFO[0000] Listening on :9100                            source="node_exporter.go:111"
ERRO[0001] ERROR: meminfo collector failed after 0.000037s: couldn't get memory: no such file or directory  source="collector.go:132" 
ERRO[0006] ERROR: meminfo collector failed after 0.000034s: couldn't get memory: no such file or directory  source="collector.go:132"
ERRO[0011] ERROR: meminfo collector failed after 0.000037s: couldn't get memory: no such file or directory  source="collector.go:132"

[discordianfish]

Yeah.. good question. Unfortunately I don't use BSD and not sure about the best way forward. But yeah in general, if we need a different behavior in dragonfly than in freebsd, we'd need separate files with build flags to build only the right one.

[iori-yja]

One of the possible solutions is to add a tiny logic to check the availability of data with vm.swap_total and use vm.swap_size if not. I think that's very very easy, but I couldn't see such workaround in other collectors. 🤔

[iori-yja]

if we need a different behavior in dragonfly than in freebsd, we'd need separate files with build flags to build only the right one.

That's good because it keeps them simple. On the other hand, keeping them together has a good point for Dragonfly users because they may stay updated thanks to many FreeBSD users.

[discordianfish]

I think a simple check to use either swap_total or swap_size is probably fine.. But still, not using BSD and not knowing how dragonfly compares to freebsd I don't really have a opinion on that.

[iori-yja]

Thank you for your advice. I think swap_size is the size in total: https://bugs.dragonflybsd.org/issues/1805#note-1, which means it is very similar to swap_total.

[iori-yja]

This issue should be closed because it has merged! Thank you 🙏 🙏

#1149

[isavcic]

Hey guys, I still see this error on FreeBSD 12.0-RELEASE.

root@freebsd:~/go/src/github.com/prometheus/node_exporter # ./node_exporter
INFO[0000] Starting node_exporter (version=0.17.0, branch=master, revision=7c960fd68365e9bbdb14cf140fc1d26d4c27333a)  source="node_exporter.go:156"
INFO[0000] Build context (go=go1.11, user=root@freebsd, date=20181218-11:33:20)  source="node_exporter.go:157"
INFO[0000] Enabled collectors:                           source="node_exporter.go:97"
INFO[0000]  - boottime                                   source="node_exporter.go:104"
INFO[0000]  - cpu                                        source="node_exporter.go:104"
INFO[0000]  - exec                                       source="node_exporter.go:104"
INFO[0000]  - filesystem                                 source="node_exporter.go:104"
INFO[0000]  - loadavg                                    source="node_exporter.go:104"
INFO[0000]  - meminfo                                    source="node_exporter.go:104"
INFO[0000]  - netdev                                     source="node_exporter.go:104"
INFO[0000]  - textfile                                   source="node_exporter.go:104"
INFO[0000]  - time                                       source="node_exporter.go:104"
INFO[0000] Listening on :9100                            source="node_exporter.go:170"
ERRO[0014] ERROR: meminfo collector failed after 0.000062s: couldn't get memory: no such file or directory  source="collector.go:132"

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