free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel. The shared memory column should be ignored; it is obsolete.
free [OPTION]
[root@server1 ~]# free
total used free shared buffers cached
Mem: 1021964 594820 427144 0 122708 279476
-/+ buffers/cache: 192636 829328
Swap: 2064376 0 2064376
-b,-k,-m,-g show output in bytes, KB, MB, or GB -l show detailed low and high memory statistics -o use old format (no -/+buffers/cache line) -t display total for RAM + swap -s update every [delay] seconds -c update [count] times -V display version information and exit