linux running out of memory

The meaning of free -g

/	total	used	free	shared	buffers	cached
Mem Total physical memory Currently used memory (including slab+buffers+cached) Totally unused memory Memory shared between processes Metadata of cached files1 Specific content of cached files1
-/+ buffers/cache currently used memory (excluding buffers+cached, but including slab) unused and cached memory (free+buffers+cached)			
Swap total swap space used swap space unused swap space			

Then top looked at it, there is no program that eats memory in particular. Use ps to roughly count the total memory occupied by all programs:

ps aux | awk '{mem += $6} END {print mem/1024/1024}'

cat /proc/meminfo

For details, please refer to
http://blog.atime.me/research/linux-ate-my-memory.html