This is a very quick and easy guide for installing the SNMP service on proxmox, this can be used to monitor your install with something like LibreNMS

Install the service
To install the service run the following command
apt-get install snmpd

Configure the service
Start by making a backup of the original config file
mv /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak

Then create the new config file by running the following
nano /etc/snmp/snmpd.conf

This is the content of the file
# this create a  SNMPv1/SNMPv2c community named "my_servers"
# and restricts access to LAN adresses (last two 0's are ranges)
rocommunity my_servers

# setup info
syslocation  "Location of server"
syscontact  "Who to contact"

# open up
agentAddress  udp:161

# run as
agentuser  root

# dont log connection from UDP:
dontLogTCPWrappersConnects yes

# fix for disks larger then 2TB
realStorageUnits 0

If you need to add an exception to the firwewall
iptables -A INPUT -s -p udp --dport 161 -j ACCEPT

Finally you need to start the service
# debian starts services on install
service snmpd restart

Lastly you can enable it by default
update-rc.d snmpd enable

Time to test
Once all the above is completed you need to test the config

Run the following
snmpwalk -c my_server -v1 servername SNMPv2-MIB::sysDescr.0

This should provide output similar to the following
SNMPv2-MIB::sysDescr.0 = STRING: Linux  ...