free—Display amount of free and used memory in the system
free [-b | -k | -m] [-o] [-s delay] [-t]
free displays the total amount of free and used physical and swap memory in the system, as well as the shared memory and buffers used by the kernel.
The -b switch displays the amount of memory in bytes; the -k switch (set by default) displays it in kilobytes; the -m switch displays it in megabytes.
The -t switch displays a line containing the totals.
The -o switch disables the display of a “buffer adjusted” line. Unless specified free subtracts/adds buffer memory from/to the used/free memory reports (respectively!).
The -s switch activates continuous polling delay seconds apart. You may actually specify any floating point number for delay, usleep(3) is used for microsecond resolution delay times.