SNMP Custom OID

[Thorgear]

I need to define a custom OID. I think the correct place to do it is in /tmp/snmpd.conf, but that's a temporary file. Does anyone know the correct place to define the custom OID?

 

[ColinTaylor]

What router/firmware? Or are we meant to be mind readers?

 

[Thorgear]

Ah, right. I forgot that I wasn't in a Merlin forum. It's an ASUS AC68 running Merlin 380_60_beta2, but I think the answer is applicable to my other Merlin routers. I'm adding this line to /tmp/snmpd.conf:

exec .1.3.6.1.4.1.32473.8.1 gfgf /opt/gf.sh

I can add it and restart snmpd in a startup script, but I'd rather do it the right way, if there is such a thing.

 

[RMerlin]

Ah, right. I forgot that I wasn't in a Merlin forum. It's an ASUS AC68 running Merlin 380_60_beta2, but I think the answer is applicable to my other Merlin routers. I'm adding this line to /tmp/snmpd.conf:

exec .1.3.6.1.4.1.32473.8.1 gfgf /opt/gf.sh

I can add it and restart snmpd in a startup script, but I'd rather do it the right way, if there is such a thing.

The documentation is your best friend here:

https://github.com/RMerl/asuswrt-merlin/wiki/Custom-config-files

 

[Thorgear]

Ugh. I can't believe I forgot about that. Rookie mistake.

Thanks for your help.

 

[Thorgear]

I have a follow-up question. One of the things I'm trying to do is get back a rough memory-free percentage for a PRTG sensor. In this case, it's from a Tomato router. These are the changes I'm making and the results.

Tomato router: snmpd.conf:
sh .1.3.6.1.4.1.32473.8.2 memfree /jffs/memfree.sh

Tomato router: memfree.sh:
cat /proc/meminfo | awk '/MemFree/ {free=$2} /MemTotal/ {total=$2} END {printf ("%2.2f\n", (free/total)*100)}'

Windows client:
c:\usr\bin\snmpwalk.exe -v 2c -c public 10.0.3.1 .1.3.6.1.4.1.32473.8.2

Result:
SNMPv2-SMI::enterprises.32473.8.2.1.1 = INTEGER: 1
SNMPv2-SMI::enterprises.32473.8.2.2.1 = STRING: "memfree"
SNMPv2-SMI::enterprises.32473.8.2.3.1 = STRING: "/jffs/memfree.sh"
SNMPv2-SMI::enterprises.32473.8.2.100.1 = INTEGER: 0
SNMPv2-SMI::enterprises.32473.8.2.102.1 = INTEGER: 0

The same changes work fine on a Merlin router.

SNMPv2-SMI::enterprises.32473.8.2.1.1 = INTEGER: 1
SNMPv2-SMI::enterprises.32473.8.2.2.1 = STRING: "gstats"
SNMPv2-SMI::enterprises.32473.8.2.3.1 = STRING: "/jffs/memfree.sh"
SNMPv2-SMI::enterprises.32473.8.2.100.1 = INTEGER: 0
SNMPv2-SMI::enterprises.32473.8.2.101.1 = STRING: "69.38"
SNMPv2-SMI::enterprises.32473.8.2.102.1 = INTEGER: 0
SNMPv2-SMI::enterprises.32473.8.2.103.1 = ""

Any idea what I might be doing wrong?

 

[ColinTaylor]

Well at the risk of stating the obvious, your script is not producing any output (.101.1).

Two things to check;
1) Is the script running at all?
2) If it is running perhaps the "cat ..." command is hanging/crashing.

I suggest that you test for 2) by replacing the "cat ..." command with "echo 99.9" and see if that gives you any output.

 

[Thorgear]

Well at the risk of stating the obvious, your script is not producing any output (.101.1).

Yep, that's the problem.

1) Is the script running at all?

It's definitely running. I used logger to prove that memfree.sh starts and finishes.

2) If it is running perhaps the "cat ..." command is hanging/crashing.

Maybe, but it works if I run memfree.sh manually from a shell.

I suggest that you test for 2) by replacing the "cat ..." command with "echo 99.9" and see if that gives you any output.

Already tried that. I see the logger output in the log, but not the echo. However, it works from a shell.

memfree.sh:
#!/bin/sh
logger "### START ###"
echo xxxxx
logger "### END ###"

Invoked from the Windows client:
c:\usr\bin\snmpwalk.exe -v 2c -c public 10.0.3.1 .1.3.6.1.4.1.32473.8.2

Returns:
SNMPv2-SMI::enterprises.32473.8.2.1.1 = INTEGER: 1
SNMPv2-SMI::enterprises.32473.8.2.2.1 = STRING: "memfree"
SNMPv2-SMI::enterprises.32473.8.2.3.1 = STRING: "/jffs/memfree.sh"
SNMPv2-SMI::enterprises.32473.8.2.100.1 = INTEGER: 0
SNMPv2-SMI::enterprises.32473.8.2.102.1 = INTEGER: 0

And in the log:
Jul 24 19:59:27 unknown user.notice root: ### START ###
Jul 24 19:59:27 unknown user.notice root: ### END ###

Invoked from a shell on the router:
memfree.sh

Returns:
xxxxx

And in the log:
Jul 24 20:00:47 unknown user.notice root: ### START ###
Jul 24 20:00:47 unknown user.notice root: ### END ###

I feel like I'm missing something obvious. What do you think?

 

[Thorgear]

FYI, it doesn't work when I echo a number either. I think the interesting part is that it skips 101.1.

 

[ColinTaylor]

Hmm. I can only think that it's a peculiarity of the version of snmpd on the router.

How about trying this in snmpd.conf instead. Although I can't imagine why it would make a difference.

exec .1.3.6.1.4.1.32473.8.2 memfree /bin/sh /jffs/memfree.sh

 

[Thorgear]

Hmm. I can only think that it's a peculiarity of the version of snmpd on the router.

How about trying this in snmpd.conf instead. Although I can't imagine why it would make a difference.

exec .1.3.6.1.4.1.32473.8.2 memfree /bin/sh /jffs/memfree.sh

Excellent idea - it worked! It's the exec that fixed it.

Thank you so much! I never would have thought of that.

 

[ColinTaylor]

Wow. That's a lucky guess.

Was it the exec command vs. sh ? I thought they were meant to be synonymous.

Or was if because of the change from "/jffs/memfree.sh" to "/bin/sh /jffs/memfree.sh"? (Perhaps sysout was getting lost because of the way the shell was being spawned).

 

[Thorgear]

Maybe lucky, but they were still good leads. It turned out that changing from sh to exec did the trick. Deliberately spawning a shell (/bin/sh) didn't change anything.

I think exec and sh are basically the same, but sh forces a new shell. Exec only spawns a shell if the target is a script. In this case, if one of exec or sh worked, I would expect it to be sh. Either I'm wrong, or the behavior on Tomato is reversed.