正确理解 output of linux command free

iteye_9496

于 2016-10-04 08:46:34 发布

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本文解析了Linux中free命令的使用方法及其输出含义，通过实例详细解释了如何查看系统的内存使用情况，包括总内存、已用内存、空闲内存、缓存和交换分区等。

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linux command free is used to show the RAM usage of the system. Below is an example output of the command:

$ free -m

total used free shared buffers cached

Mem: 2000 1921 78 0 6 34

-/+ buffers/cache: 1881 119

Swap: 0 0 0

The "-m" switch outputs in megabyte. So the system:

has total RAM of 2G.
Used 1921M, but in this Used Mem, it includes 6M as buffers and 34M for cached data.
Absolutely free (not used by anything) memory is 78M.
If necessary, the system can use the buffered and cached memory for other processes. Therefore, the actual used memory is "used" - "buffers" - "cached", ie. 1921 - 6 - 34 = 1881M. This is lised on the 2nd line of the output: "-/+ buffers/cache 1881 119".
Note the "-/+ buffers/cache 1881 119" has a "-/+" at the beginning. I think "-" means what we talked about in point 4. While "+" means that the actual free memory is "free" + "buffers" + "cached" = 78 + 6 + 34 (roughly 119M). Since the system can use that 119M for other processes (at most 119M can be allocated as free memory).