使用 free -m 命令查看内存使用情况时，发现2个不同版本的CentOS系统显示的结果不同，
系统一：
free -m
total used free shared buffers cached
Mem: 992 926 66 83 118 148
-/+ buffers/cache: 659 333
Swap: 0 0 0 codebye.com
系统二：
free
total used free shared buff/cache available
Mem: 1012720 121728 735008 37724 155984 814736
Swap: 524284 33284 491000
搜索后发现：
free: remove -/+ buffers/cache
With introduction of the 'available' column and with the latest changes in the 'used' evaluation the -/+ buffers/cache line became redundant. The first value duplicates the 'used' column and the second value has a more accurate brother called 'available'. www.codebye.com copyright
新版本中 free 命令已经不显示 -/+ buffers/cache
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