SNMP Table input fails on Windows

[pstatho]

Bug report

SNMP Table input fails on Windows.

Relevant telegraf.conf:

[[inputs.snmp]]
  agents = [ "10.20.254.10:161" ]
  version = 1
  community = "public"
  name = "Switches"
  [[inputs.snmp.field]]
    name = "hostname"
    oid = "RFC1213-MIB::sysName.0"
    is_tag = true
  [[inputs.snmp.field]]
    name = "uptime"
    oid = "DISMAN-EXPRESSION-MIB::sysUpTimeInstance"	
  
  [[inputs.snmp.table]]
    name = "iface"
	inherit_tags = [ "hostname" ]
    oid = "IF-MIB::ifTable"
	# Interface tag - used to identify interface in metrics database
    [[inputs.snmp.table.field]]
      name = "ifDescr"
      oid = "IF-MIB::ifDescr"
      is_tag = true

System info:

Telegraf v1.4 on Windows 2012R2

Steps to reproduce:

1. Install net-snmp 5.7 for Windows
2. Use the CONFIG EXAMPLES from the SNMP plugin as above

Expected behavior:

SNMP Table info is collected and sent to InfluxDB

Actual behavior:

SNMP plugin fails to collect table data

Additional info:

Log file contains the following error:

2017-09-25T04:41:40Z E! Error in plugin [inputs.snmp]: initializing table iface: getting table columns: exit status 1: IF-MIB::ifTable

I believe the error is occurring on line 876 of snmp.go file. My understanding is that it is running the command:

snmptable -Ch -Cl -c public 127.0.0.1 IF-MIB::ifTable

When I run that command from the command line, it returns the table columns and I checked the exit code which is 0.

Use case: [Why is this important (helps with prioritizing requests)]

Pretty important for Windows sysadmins to use TICK to collect SNMP data in an office environment

[danielnelson]

I wonder if this is a permissions or environment issue, how are you running telegraf?

[pstatho]

Telegraf is running a windows service as per documentation. If I comment out just the [[inputs.snmp.table]] section telegraf will get the other SNMP values properly.
In fact when I'm collecting an individual index (port) from IF-MIB::ifTable is works no problem and is sent to InfluxDB as expected. Only when I use the table option it fails.

Also like I mentioned, I'm pretty sure it's failing when calling snmpwalk to get the headers, since the error message happens right after that check.

[pstatho]

I just tried in another environment with another network device and I get the same error. I believe it's the way Go is wrapping and calling the net-snmp commands. BTW, yes the net-snmp commands work properly since I can call
snmpwalk -v 1 -c public 10.20.254.10 IF-MIB::ifTable
and it will return the results of tha table as expected.

[RubenN]

Same here on a windows 10 64 bit system:
2017-10-19T13:46:00Z E! Error in plugin [inputs.snmp]: initializing table interface: getting table columns: exit status 1: IF-MIB::ifTable

[danielnelson]

I did a little investigation and it appears that this is caused by DOS line endings in the command output in Windows.

[pstatho]

Thanks @danielnelson, would you know of a temporary workaround or do we have to wait till this bug is corrected?

[RubenN]

I put part of the logic in a little test program:

...
oidFullName := "IF-MIB::ifTable"
// this won't actually try to run a query. The `-Ch` will just cause it to dump headers.
out, err := execCmd("snmptable", "-Ch", "-Cl", "-c", "public", "127.0.0.1", oidFullName)
if err != nil {
	fmt.Println(err.Error())
} 
...

And this doesn't trigger the error part.

[danielnelson]

@pstatho You might be able to create a wrapper script that converts to unix line endings, and wrap both snmptranslate and snmptable. I haven't tried this so I'm not sure if it will work.

@RubenN It is not actually a problem with running the commands, but with parsing the output. When we parse the oidText here it has a trailing \r. This breaks the later running of snmptable because the args are invalid.

[pstatho]

@danielnelson the line parsing does sound like it's the issue. I suppose using ReadLine() instead would make it cross-platform. BTW, it's also used on several other lines like 850 and 877 and 970