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17.2. Viewing Memory Usage

17.2.1. Using the free Command

The free command allows you to display the amount of free and used memory on the system. To do so, type the following at a shell prompt:
free
The free command provides information about both the physical memory (Mem) and swap space (Swap). It displays the total amount of memory (total), as well as the amount of memory that is in use (used), free (free), shared (shared), in kernel buffers (buffers), and cached (cached). For example:
~]$ free
             total       used       free     shared    buffers     cached
Mem:        761956     607500     154456          0      37404     156176
-/+ buffers/cache:     413920     348036
Swap:      1540092      84408    1455684
By default, free displays the values in kilobytes. To display the values in megabytes, supply the -m command line option:
free -m
For instance:
~]$ free -m
             total       used       free     shared    buffers     cached
Mem:           744        593        150          0         36        152
-/+ buffers/cache:        404        339
Swap:         1503         82       1421
For a complete list of available command line options, refer to the free(1) manual page.