Understanding free output in Linux


If you are managing Linux machines daily like me, its important to understnad the output of free command, which shows the free system memory.

[[email protected] vagrant]# free
              total        used        free      shared  buff/cache   available
Mem:        5824332     2292284     1155732      132980     2376316     3087844
Swap:        839676       18172      821504
[[email protected] vagrant]#

free -g is much more helpful instead

[[email protected] vagrant]# free -g
              total        used        free      shared  buff/cache   available
Mem:              5           2           1           0           2           2
Swap:             0           0           0
[[email protected] vagrant]#

Some flavours of linux might output in this format:

             total       used       free     shared    buffers     cached
Mem:            62         46         16          0          0         10
-/+ buffers/cache:         35         27
Swap:            0          0          0
-----------------------------
  • total - Your total, physical (assuming no virtualization) memory
  • used - How much of that is currently used (by anything)
  • free - How much of that is completely free (not used at all)
  • shared - (never anything there, ignore that column)
  • buffers - Memory used by kernel buffers
  • cached - Memory used for cache

Essentially, the figures which we should be focussing on is -/+ buffers/cache which excludes the used buffer.