I use free
to get the amount of free space on some of my servers. Its output is something like:
$ free -m
total used free shared buffers cached
Mem: 374 366 8 0 58 98
-/+ buffers/cache: 209 165
Swap: 1906 120 1785
How much free space do I really have?
Best Answer
The first line of the
free
output lists:total
Your total, physical (assuming no virtualization) memoryused
How much of that is currently used (by anything)free
How much of that is completely free (not used at all)shared
Memory used (mostly) by tmpfs (for Linux, kernel >= 2.6.32)buffers
Memory used by kernel bufferscached
Memory used for cacheThe last two items, cache and buffers, is memory that is not allocated to specific user processes. It is memory reserved by the kernel to improve performance overall, but is not "application" memory. These areas will grow or shrink depending on kernel policies with respect to caching, memory pressure, application I/O patterns, etc.
Since these two columns are not user-allocated memory, and the zones can shrink (practically to zero) if user allocations require it, they are in a sense "free" - there's RAM there that can be freed up by the kernel if your apps actively need it.
That's what the second line tells you. It removes the buffer and cache memory from the
used
column (that's what the-
means), and adds (+
) them to thefree
column. (Rounding issue will happen.)(The last line shows the state of your swap space.)