20.2. Viewing Memory Usage

20.2.1. 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), sum of buffers and cached (buff/cache), and available (available). For example:
~]$ free
              total        used        free      shared  buff/cache   available
Mem:        1016800      727300       84684        3500      204816      124068
Swap:        839676       66920      772756
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  buff/cache   available
Mem:            992         711          81           3         200         120
Swap:           819          65         754
For a complete list of available command line options, see the free(1) manual page.

20.2.2. Using the System Monitor Tool

The Resources tab of the System Monitor tool allows you to view the amount of free and used memory on the system.
To start the System Monitor tool from the command line, type gnome-system-monitor at a shell prompt. The System Monitor tool appears. Alternatively, if using the GNOME desktop, press the Super key to enter the Activities Overview, type System Monitor and then press Enter. The System Monitor tool appears. The Super key appears in a variety of guises, depending on the keyboard and other hardware, but often as either the Windows or Command key, and typically to the left of the Spacebar.
Click the Resources tab to view the system's memory usage.
System Monitor — Resources

Figure 20.2. System Monitor — Resources

In the Memory and Swap History section, the System Monitor tool displays a graphical representation of the memory and swap usage history, as well as the total amount of the physical memory (Memory) and swap space (Swap) and how much of it is in use.