Ubuntu Manpage: free - Display amount of free and used memory in the system

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 represents either the MemShared value (2.4 series kernels) or the Shmem value (2.6 series kernels and later) taken from the /proc/meminfo file. The value is zero if none of the entries is exported by the kernel.

OPTIONS

-b, --bytes

Display the amount of memory in bytes.

-k, --kilo

Display the amount of memory in kilobytes. This is the default.

-m, --mega

Display the amount of memory in megabytes.

-g, --giga

Display the amount of memory in gigabytes.

--tera

Display the amount of memory in terabytes.

-h, --human

Show all output fields automatically scaled to shortest three digit unit and display the units of print out. Following units are used.

  B = bytes
  K = kilos
  M = megas
  G = gigas
  T = teras

If unit is missing, and you have petabyte of RAM or swap, the number is in terabytes and columns might not be aligned with header.

-c, --count count

Display the result count times. Requires the -s option.

-l, --lohi

Show detailed low and high memory statistics.

-o, --old

Display the output in old format, the only difference being this option will disable the display of the "buffer adjusted" line.

-s, --seconds seconds

Continuously display the result delay seconds apart. You may actually specify any floating point number for delay, usleep(3) is used for microsecond resolution delay times.

--si