#man free
NAME
free - Display amount of free and used memory in the system
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
[root@localhost ~]# free -h free: invalid option -- h usage: free [-b|-k|-m|-g] [-l] [-o] [-t] [-s delay] [-c count] [-V] -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 [root@localhost ~]#
# free -m
total used free shared buff/cache available
Mem: 992 381 87 53 524 357
Swap: 2047 7 2040
Total : 992MB
Used Memory : 635MB = 992MB - 357MB
Free Memory : 357MB
[root@localhost ~]# free
total used free shared buffers cached
Mem: 515488 169284 346204 0 9040 127436
-/+ buffers/cache: 32808 482680
Swap: 1048568 0 1048568
Total : 515488Kbyte
Used Memory： 32808Kbyte = 169284Kbyte - 9040Kbyte - 127436Kbyte
Free Memory： 482680Kbyte = 346204Kbyte + 9040Kbyte + 127436Kbyte
[root@localhost ~]# free -m
total used free shared buffers cached
Mem: 503 165 338 0 8 124
-/+ buffers/cache: 32 471
Swap: 1023 0 1023
Total : 503MB
Used Memory：32MB = 165MB - 8MB - 124MB
Free Memory：471MB = 338MB + 8MB + 124MB
Used Memory ＝ Total - Available Free Memory ＝ Available
Used Memory ＝used - buffers - cached Free Memory ＝ free + buffers + cached