The official ArchLinux package for net-snmp does not come with lm_sensors support, consequently the corresponding MIB is missing. Here is how to customize and compile the package to get sensors suppors.

We will use the Arch Build System (ABS) to first, install and run ABS to retrieve the PKGBUILD scripts from the Arch Linux repositories:

shell> pacman -S abs base-devel
# (edited, usual output)
shell> abs
# (edited, lots of output here)

Then copy the net-snmpd package to a custom location:

shell> cp -r /var/abs/extra/net-snmpd ~/abs_workspace
shell> cd ~/abs_workspace/net-snmp

Now edit the PKGBUILD and look for the line starting the flag --with-mib-modules and append ucd-snmp/lmsensorsMib to it. As of date, it is line #44 and the resulting line is:

--with-mib-modules="host misc/ipfwacc ucd-snmp/diskio tunnel ucd-snmp/dlmod ucd-snmp/lmsensorsMib" \

Now build the package and install it:

shell> makepkg -s --skippgpcheck
shell> pacman -U
shell> systemctl daemon-reload
shell> systemctl restart

Now for the test:

shell> snmpwalk -v 2c -c public localhost lmSensors
# following is just a sample of the line you should get:
LM-SENSORS-MIB::lmTempSensorsIndex.1 = INTEGER: 1
LM-SENSORS-MIB::lmTempSensorsDevice.1 = STRING: Physical id 0
LM-SENSORS-MIB::lmTempSensorsValue.1 = Gauge32: 33000

You may have notice I used the --skippgpcheck flag with makepkg. See this post for more information.