That's because your SNMP on your linux host is not configured properly. My guess is that you're using default settings.
You need to modify your /etc/snmp/snmpd.conf file.
Near the top you'll see rocommunity and rwcommunity lines, if they aren't there they need to be set:
rocommunity yourstring
rwcommunity yourstring
Replace yourstring with whatever you want (it is very bad security practice to leave it as public).
Near the bottom fo the file you'll want lines such as:
com2sec paranoid default public
group MyROSystem v1 paranoid
group MyROSystem v2c paranoid
group MyROSystem usm paranoid
group MyROGroup v1 readonly
group MyROGroup v2c readonly
group MyROGroup usm readonly
group MyRWGroup v1 readwrite
group MyRWGroup v2c readwrite
group MyRWGroup usm readwrite
view all included .1 80
view system included .iso.org.dod.internet.mgmt.mib-2.system
access MyROSystem "" any noauth exact system none none
access MyROGroup "" any noauth exact all none none
access MyRWGroup "" any noauth exact all all none
You only have access to part of the snmp tree at the moment, hence why you are seeing those debug messages relating to memAvailReal and such.
