Missing RAM

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josephmartinez
Posts: 3
Joined: 2014/12/26 09:11:20

Missing RAM

Post by josephmartinez » 2015/09/23 00:26:52

I'm noticing only 6.5GB of RAM when BIOS sees my RAM total at 8GB (1x8). As far as I can tell this only started when I installed CentOS. Before I was dual-booting Windows and Fedora 22 - now Windows and CentOS 7.

[root@home ~]# cat /proc/meminfo |grep -i memtotal
MemTotal: 6854780 kB

[root@home ~]# dmesg |grep Memory
[ 0.000000] Memory: 6785392k/8896512k available (6243k kernel code, 1615864k absent, 495256k reserved, 4180k data, 1604k init)

I'm not even sure where to begin troubleshooting this. Is there way to test from Linux to see why it sees 1.5GB of RAM missing?

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TrevorH
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Location: Brighton, UK

Re: Missing RAM

Post by TrevorH » 2015/09/23 00:40:22

Run dmesg | less and look at the first lines of output from the kernel. They probably begin with BIOS-e820. They detail the memory map that the kernel has got from a BIOS call. One possible reason might be that you have an onboard video card that shares your RAM to do its job and you have told it to use, say, 1GB. That would reduce the amount available to the o/s by 1GB. If you have trouble interpreting the output then post dmesg | grep -i e820 wrapped in code tags to preserve the formatting.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

josephmartinez
Posts: 3
Joined: 2014/12/26 09:11:20

Re: Missing RAM

Post by josephmartinez » 2015/09/26 12:52:44

Here's the output of "dmesg |grep -i e820":

Code: Select all

[root@home ~]# dmesg |grep -i e820
[    0.000000] e820: BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000006dfff] usable
[    0.000000] BIOS-e820: [mem 0x000000000006e000-0x000000000006ffff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x0000000000070000-0x0000000000085fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000000086000-0x00000000000bffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000092a22fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000092a23000-0x0000000093223fff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000093224000-0x000000009327bfff] usable
[    0.000000] BIOS-e820: [mem 0x000000009327c000-0x000000009427bfff] reserved
[    0.000000] BIOS-e820: [mem 0x000000009427c000-0x000000009ee7efff] usable
[    0.000000] BIOS-e820: [mem 0x000000009ee7f000-0x000000009fa7efff] reserved
[    0.000000] BIOS-e820: [mem 0x000000009fa7f000-0x000000009fb7efff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x000000009fb7f000-0x000000009fbfefff] ACPI data
[    0.000000] BIOS-e820: [mem 0x000000009fbff000-0x000000009fbfffff] usable
[    0.000000] BIOS-e820: [mem 0x000000009fc00000-0x00000000dfffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fec00000-0x00000000fec00fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed80000-0x00000000fed80fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000ff800000-0x00000000ffffffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000021effffff] usable
[    0.000000] e820: update [mem 0x925ee018-0x925fd657] usable ==> usable
[    0.000000] e820: update [mem 0x925e1018-0x925ed057] usable ==> usable
[    0.000000] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.000000] e820: last_pfn = 0x21f000 max_arch_pfn = 0x400000000
[    0.000000] e820: last_pfn = 0x9fc00 max_arch_pfn = 0x400000000
[    0.000000] tboot: non-0 tboot_addr but it is not of type E820_RESERVED
[    0.000000] e820: [mem 0xe0000000-0xf7ffffff] available for PCI devices
[    0.203168] PCI: MMCONFIG at [mem 0xf8000000-0xfbffffff] reserved in E820
[    7.607814] e820: reserve RAM buffer [mem 0x0006e000-0x0006ffff]
[    7.607817] e820: reserve RAM buffer [mem 0x00086000-0x0008ffff]
[    7.607819] e820: reserve RAM buffer [mem 0x925e1018-0x93ffffff]
[    7.607821] e820: reserve RAM buffer [mem 0x925ee018-0x93ffffff]
[    7.607823] e820: reserve RAM buffer [mem 0x92a23000-0x93ffffff]
[    7.607825] e820: reserve RAM buffer [mem 0x9327c000-0x93ffffff]
[    7.607827] e820: reserve RAM buffer [mem 0x9ee7f000-0x9fffffff]
[    7.607828] e820: reserve RAM buffer [mem 0x9fc00000-0x9fffffff]
[    7.607830] e820: reserve RAM buffer [mem 0x21f000000-0x21fffffff]
I'm not sure what any of this really means. Any input would be appreciated. Thanks!

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