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Maciej Wawrzyńczuk
Asked: 2018-08-15 04:46:05 +0800 CST

Linux - memory size

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How to check exact amount of memory installed in server? MemTotal from /proc/meminfo show something a bit less. I.e. I have 2097152K and meminfo says 2054348K.

I can sum all banks reported by dmidecode but it requires reboot to update - I don't like it.

Any other ideas? I'm writing test for automated provisioning in vmware environment and I want to do it right. :)

linux

1 Answers

  1. As to why MemTotal is missing some memory: https://serverfault.com/a/219990/37681 

     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
      bits and the kernel binary code)

    As long as the kernel message buffer hasn't been filled with more recent events: look for a line starting with Memory in dmesg: 

    # dmesg |grep " Memory:"
[    0.000000] Memory: 8125008K/8388088K available (8546K kernel code, 1313K rwdata, 4000K rodata, 1516K init, 1316K bss, 263080K reserved, 0K cma-reserved)

    which shows the physical ram: 8388088K and the "few reserved bits and the kernel binary code" 263080K and the rest is available for the applications 8125008K and what will be shown as MemTotal in /proc/meminfo.

    (Later stages in the boot process will free up some additional memory, increasing MemTotal, btw dmesg |grep Freeing)

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