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The shared memory column should be ignored; it is obsolete.
Options 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.
If the -o option is not specified, free subtracts buffer memory
from the used memory and adds it to the free memory reported.
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.