24.2. Viewing Memory Usage

24.2.1. 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:        760752     661332      99420          0       6476     317200
-/+ buffers/cache:     337656     423096
Swap:      1540088     283652    1256436
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:           742        646         96          0          6        309
-/+ buffers/cache:        330        412
Swap:         1503        276       1227
For a complete list of available command-line options, see the free(1) manual page.