free -m 内存

    查看内存及交换swap分区大小及使用率

man  free

NAME
       free - Display amount of free and used memory in the system

SYNOPSIS
       free [-b | -k | -m] [-o] [-s delay ] [-t] [-l] [-V]

DESCRIPTION
       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 mem-
       ory column should be ignored; it is obsolete.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.

       The -l switch shows detailed low and high memory statistics.

       The -V switch displays version information.

FILES
       /proc/meminfo-- memory information

free   -m  -s   6    ###每隔6s输出一次 

[root@VM_0_3_centos ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          3830       3723        107          0        240       1604
-/+ buffers/cache:       1878       1952
Swap:            0          0          0

 计算方式

191272k total  物理内存总量 
173656k used  使用的物理内存总量 
17616k free  空闲内存总量 

total =  userd + free
22052k buffers  用作内核缓存 的内存量 
123988k cached  缓冲的交换区总量。
-/+buffters/cache-userd =  mem-userd  - buffters - cached

swap  交换分区信息