While starting Nexus I was getting following error, this was on a machine that was running at 1GB of memory.
Error occurred during initialization of VM
Could not reserve enough space for object heap
So the solution was to edit
wrapper.java.additional.4=-Xmx128m parameter this setup java to use only 128mb of memory for the new VM.
After further analysis of the config file there are following options that can be set as well, just need to uncomment them
# Size Java memory, in MB (-Xms)
# Size Java memory, in MB (-Xmx)