前面我们介绍过, 通过 top 或者 htop 命令能够查看服务器的物理机内存和 Swap 的使用情况, 除了这两种工具, 我们其实还会有些其他工具,完成类似的任务.

free 命令用于显示内存的使用信息, 比如

root@server:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           3.9G        1.5G        1.1G        5.9M        1.3G        2.1G
Swap:          974M          0B        974M

除了类似 top 命令显示的 totalusedfreebuff/cache,还显示了 sharedavailable等信息。

这里有些内存概念需要我们知道:

  • Cache 作为加载到内存中的磁盘数据,用于快速访问。
  • Swap 是磁盘上的交换分区,被系统用来在物理内存紧张的情况下, 将使用频率低的内存页面交换到磁盘, 以便释放更多物理内存给系统使用。

更多free命令的内存可以查看 man free

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

SYNOPSIS
       free [options]

DESCRIPTION
       free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is gathered by parsing /proc/meminfo. The displayed columns are:

       total  Total installed memory (MemTotal and SwapTotal in /proc/meminfo)

       used   Used memory (calculated as total - free - buffers - cache)

       free   Unused memory (MemFree and SwapFree in /proc/meminfo)

       shared Memory used (mostly) by tmpfs (Shmem in /proc/meminfo, available on kernels 2.6.32, displayed as zero if not available)

       buffers
              Memory used by kernel buffers (Buffers in /proc/meminfo)

       cache  Memory used by the page cache and slabs (Cached and Slab in /proc/meminfo)

       buff/cache
              Sum of buffers and cache

       available
              Estimation  of  how  much  memory  is  available  for  starting  new  applications, without swapping. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all
              reclaimable memory slabs will be reclaimed due to items being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free)

free 有些比较有用的选项:

  • -b or --bytes 以字节为单位显示内存信息
  • -k or --kilo 以k为单位显示内存信息
  • -m or --mega 以m为单位显示内存信息
  • -g or --giga 以g为单位显示内存信息
  • --tera 以t为单位显示内存信息
  • -h or --human 以便于人可读的信息显示内存信息

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标签: free, 内存监控

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