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What do buffers and cached stand for in free output? discussion

free reference

Your total (physical) RAM; used + free.
memory in use by the OS.

memory not in use.

shared / buffers / cached

This shows memory usage for specific purposes, these values are included in the value for used.

The second line gives first line values adjusted. It gives the original value for used minus the sum buffers + cached and the original value for free plus the sum buffers+cached, hence its title.

Linux always tries to use RAM to speed up disk operations by using available memory for buffers (file system metadata) and cache (pages with actual contents of files or block devices). If space is needed by applications, then Linux will free up the buffers and cache to yield memory for the applications.