Enable SNMP in vSphere ESX 6

First, make sure you have enabled SSH access to your ESXi node.
You can do that in Configuration > Security Profile > Services > SSH.

When SSH is enabled, login to your server with ssh root@esxi-address and type the following commands to enable a SNMP community named myc0mmun1ty with your appropriate Location and Contact.

esxcli system snmp set -r
esxcli system snmp set -c myc0mmun1ty
esxcli system snmp set -p 161
esxcli system snmp set -L "Stockholm, Sweden"
esxcli system snmp set -C noc@example.com
esxcli system snmp set -e yes

All done! Now add your host to your favourite SNMP powered monitoring tool (i.e. LibreNMS)