couldn't get SNMP6 stats on IPv6 disabled systems

[stephan2012]

Host operating system: output of uname -a

Linux testhost 3.10.0-693.2.2.el7.x86_64 #1 SMP Sat Sep 9 03:55:24 EDT 2017 x86_64 x86_64 x86_64 GNU/Linux

node_exporter version: output of node_exporter --version

node_exporter, version 0.15.0 (branch: HEAD, revision: 6e2053c557f96efb63aef3691f15335a70baaffd)
  build user:       root@168089f37ad9
  build date:       20171006-11:33:58
  go version:       go1.9.1

node_exporter command line flags

/usr/local/sbin/node_exporter --web.listen-address=0.0.0.0:3001 --collector.nfs

Are you running node_exporter in Docker?

No

What did you do that produced an error?

Run node_exporter on a IPv6 disabled Linux system (Linux kernel boot parameter ipv6.disable=1)

What did you expect to see?

No errors

What did you see instead?

node_exporter fills syslog with the error message

ERROR: netstat collector failed after 0.000297s: couldn't get SNMP6 stats: open /proc/net/snmp6: no such file or directory

node_exporter should not try to access IPv6 related information on an IPv6 disabled system. Maybe suspending accessing /proc/net/snmp6 after first failed attempt would be an option.

[mdlayher]

Easy fix. I'll take care of it.

[stephan2012]

@mdlayher: Thanks for fixing this so quickly. :-)

[mdlayher]

It appears that @iFshadow is seeing a problem even with my PR merged. When I build from master and try to open some nonsense file with this patch:

diff --git a/collector/netstat_linux.go b/collector/netstat_linux.go
index a7e7ac9..d88644a 100644
--- a/collector/netstat_linux.go
+++ b/collector/netstat_linux.go
@@ -51,7 +51,7 @@ func (c *netStatCollector) Update(ch chan<- prometheus.Metric) error {
        if err != nil {
                return fmt.Errorf("couldn't get SNMP stats: %s", err)
        }
-       snmp6Stats, err := getSNMP6Stats(procFilePath("net/snmp6"))
+       snmp6Stats, err := getSNMP6Stats(procFilePath("net/snmp6INVALID"))
        if err != nil {
                return fmt.Errorf("couldn't get SNMP6 stats: %s", err)
        }
@@ -124,6 +124,7 @@ func getSNMP6Stats(fileName string) (map[string]map[string]string, error) {
                // On systems with IPv6 disabled, this file won't exist.
                // Do nothing.
                if os.IsNotExist(err) {
+                       fmt.Println("snmp6 stats:", err)
                        return nil, nil
                }
 

I see:

INFO[0000] Listening on :9101                            source="node_exporter.go:103"
INFO[0001] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
snmp6 stats: open /proc/net/snmp6INVALID: no such file or directory

But no error message in the log that I didn't introduce.

After compiling, I continue to get an error in the log file.

version

node_exporter --version
node_exporter, version 0.15.0 (branch: , revision: f6556e6)
build user: portage@monitor
build date: 20171106-16:16:49
go version: go1.9.1

log error

time="2017-11-06T19:21:15+03:00" level=error msg="ERROR: netstat collector failed after 0.000276s: couldn't get SNMP6 stats: open /proc/net/snmp6: no such file or directory" source="collector.go:123"

uname -a

Linux monitor 4.13.4-gentoo #1 SMP Thu Oct 5 16:11:49 MSK 2017 x86_64 Intel(R) Xeon(R) CPU 5160 @ 3.00GHz GenuineIntel GNU/Linux

[mdlayher]

I can't think of any reason why you would still see this log message, especially if the version you're building has this commit.

Can you pull the latest master of node_exporter and compile with Go 1.9.2, and try again? If it still persists, can you gather some data by adding fmt.Printf("snmp6: %#v\n", err) within the getSNMP6Stats function?

I will report the results. Thanks for the quick response.

[mdlayher]

I confirm that building from master with Go 1.9.2, and running on a kernel with IPv6 disabled reports no error for me:

root@node01:~# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.4.0-97-generic root=UUID=4e8e8046-457b-49ca-b4ed-78676a0fd2ab ro ipv6.disable=1 console=tty1 console=ttyS0

root@node01:~# ./node_exporter 
INFO[0000] Starting node_exporter (version=, branch=, revision=)  source="node_exporter.go:78"
INFO[0000] Build context (go=go1.9.2, user=, date=)      source="node_exporter.go:79"
INFO[0000] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
INFO[0000] Enabled collectors:                           source="node_exporter.go:86"
INFO[0000]  - time                                       source="node_exporter.go:88"
INFO[0000]  - filesystem                                 source="node_exporter.go:88"
INFO[0000]  - sockstat                                   source="node_exporter.go:88"
INFO[0000]  - zfs                                        source="node_exporter.go:88"
INFO[0000]  - filefd                                     source="node_exporter.go:88"
INFO[0000]  - ipvs                                       source="node_exporter.go:88"
INFO[0000]  - textfile                                   source="node_exporter.go:88"
INFO[0000]  - cpu                                        source="node_exporter.go:88"
INFO[0000]  - hwmon                                      source="node_exporter.go:88"
INFO[0000]  - edac                                       source="node_exporter.go:88"
INFO[0000]  - infiniband                                 source="node_exporter.go:88"
INFO[0000]  - timex                                      source="node_exporter.go:88"
INFO[0000]  - entropy                                    source="node_exporter.go:88"
INFO[0000]  - arp                                        source="node_exporter.go:88"
INFO[0000]  - netdev                                     source="node_exporter.go:88"
INFO[0000]  - meminfo                                    source="node_exporter.go:88"
INFO[0000]  - mdadm                                      source="node_exporter.go:88"
INFO[0000]  - loadavg                                    source="node_exporter.go:88"
INFO[0000]  - stat                                       source="node_exporter.go:88"
INFO[0000]  - netstat                                    source="node_exporter.go:88"
INFO[0000]  - xfs                                        source="node_exporter.go:88"
INFO[0000]  - vmstat                                     source="node_exporter.go:88"
INFO[0000]  - diskstats                                  source="node_exporter.go:88"
INFO[0000]  - uname                                      source="node_exporter.go:88"
INFO[0000]  - wifi                                       source="node_exporter.go:88"
INFO[0000]  - bcache                                     source="node_exporter.go:88"
INFO[0000]  - conntrack                                  source="node_exporter.go:88"
INFO[0000] Listening on :9100                            source="node_exporter.go:103"
INFO[0009] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
INFO[0040] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
INFO[0040] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
INFO[0041] No directory specified, see --collector.textfile.directory  source="textfile.go:57"
INFO[0041] No directory specified, see --collector.textfile.directory  source="textfile.go:57"

After compiling from the master branch and updating golang to version 1.9.2, the errors have disappeared, the data is collected. Thanks for the help.