Linux查看内存命令及其对命令显示的解释

我们通过Linux查看内存free命令查看机器空闲内存时，会发现free的值很小。下面我们就来了解学习下Linux查看内存的命令和对这些命令的解释，这样大家更能够深刻理解我们的Linux查看内存命令

在Linux下查看内存我们一般用free命令：
[root@scs-2 tmp]# free
total<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> used<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> free<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> shared<wbr><wbr><wbr><wbr><wbr><wbr> buffers<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> cached<br> Mem:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 3266180<wbr><wbr><wbr><wbr><wbr><wbr> 3250004<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 16176<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 0<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 110652<wbr><wbr><wbr><wbr><wbr><wbr> 2668236<br> -/+ buffers/cache:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 471116<wbr><wbr><wbr><wbr><wbr><wbr> 2795064<br> Swap:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 2048276<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 80160<wbr><wbr><wbr><wbr><wbr><wbr> 1968116</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

下面是对Linux查看内存命令中这些数值的解释：
total:总计物理内存的大小。
used:已使用多大。
free:可用有多少。
Shared:多个进程共享的内存总额。
Buffers/cached:磁盘缓存的大小。
第三行(-/+ buffers/cached):
used:已使用多大。
free:可用有多少。
第四行就不多解释了。
区别：第二行(mem)的used/free与第三行(-/+ buffers/cache) used/free的区别。这两个的区别在于使用的角度来看，第一行是从OS的角度来看，因为对于OS，buffers/cached 都是属于被使用，所以他的可用内存是16176KB,已用内存是3250004KB,其中包括，内核（OS）使用+Application(X, oracle,etc)使用的+buffers+cached.
第三行所指的是从应用程序角度来看，对于应用程序来说，buffers/cached 是等于可用的，因为buffer/cached是为了提高文件读取的性能，当应用程序需在用到内存的时候，buffer/cached会很快地被回收。
所以从应用程序的角度来说，可用内存=系统free memory+buffers+cached。
如上例：
2795064=16176+110652+2668236

接下来解释什么时候内存会被交换，以及按什么方交换。 当可用内存少于额定值的时候，就会开会进行交换。
Linux查看内存命令时如何看额定值：
cat /proc/meminfo
[root@scs-2 tmp]# cat /proc/meminfo
MemTotal:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 3266180 kB<br> MemFree:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 17456 kB<br> Buffers:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 111328 kB<br> Cached:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 2664024 kB<br> SwapCached:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 0 kB<br> Active:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 467236 kB<br> Inactive:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 2644928 kB<br> HighTotal:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 0 kB<br> HighFree:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 0 kB<br> LowTotal:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 3266180 kB<br> LowFree:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 17456 kB<br> SwapTotal:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 2048276 kB<br> SwapFree:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 1968116 kB<br> Dirty:<wbr><wbr> 8 kB<br> Writeback:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 0 kB<br> Mapped:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 345360 kB<br> Slab:<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> 112344 kB<br> Committed_AS:<wbr><wbr><wbr><wbr> 535292 kB<br> PageTables:<wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>