The free command displays the total amount of physical memory and swap space for the system as well as the amount of memory that is used, free, shared, in kernel buffers, and cached. Following is a sample output of the free command:
total used free shared buffers cached Mem: 256812 240668 16144 105176 50520 81848 -/+ buffers/cache: 108300 148512 Swap: 265032 780 264252
Using the free -m command shows the same information in megabytes, which are easier to read.
total used free shared buffers cached Mem: 250 235 15 102 49 79 -/+ buffers/cache: 105 145 Swap: 258 0 258
If you prefer a graphical interface for free, you can use the GNOME System Monitor. To start the System Monitor from the desktop, click the Main Menu button and choose System Tools > System Monitor (or type gnome-system-monitor at a shell prompt from within X Window System). Then choose the System Monitor tab.
25-2. : GNOME System Monitor — System Monitor Tab