我运行free -m后发现有 245 MB 可用 RAM，而我有 8 GB！
我的 BIOS 检测到 8 GB！
我该怎么做才能恢复 RAM 空间？
free -m输出如下：
total used free shared buffers cached
Mem: 239 228 11 0 0 25
-/+ buffers/cache: 201 38
Swap: 507 136 371
uname -a给了我这个：
Linux httpcs-9 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:24 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
lshw -C memory 给了我这个：
*-firmware
description: BIOS
vendor: Winbond Electronics
physical id: 0
version: A07
date: 04/25/2008
size: 64KiB
capacity: 960KiB
capabilities: isa pci pnp upgrade shadowing escd cdboot bootselect edd int13floppytoshiba int13floppy360 int13floppy1200 int13floppy720 int5printscreen int9keyboard int14serial int17printer int10video acpi usb ls120boot biosbootspecification netboot
*-cache:0
description: L1 cache
physical id: 700
size: 16KiB
capacity: 16KiB
capabilities: internal write-through data
*-cache:1
description: L2 cache
physical id: 701
size: 1MiB
capacity: 2MiB
capabilities: internal write-back unified
*-cache:0
description: L1 cache
physical id: 703
size: 16KiB
capacity: 16KiB
capabilities: internal write-through data
*-cache:1
description: L2 cache
physical id: 704
size: 1MiB
capacity: 2MiB
capabilities: internal write-back unified
*-memory
description: System Memory
physical id: 1000
slot: System board or motherboard
size: 8GiB
*-bank:0
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: NLD257R22503F-D32K
vendor: 7F7F7F1600000000
physical id: 0
serial: 16530000
slot: DIMM1_A
size: 2GiB
width: 64 bits
clock: 400MHz (2.5ns)
*-bank:1
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: NLD257R22503F-D32K
vendor: 7F7F7F1600000000
physical id: 1
serial: 16467000
slot: DIMM1_B
size: 2GiB
width: 64 bits
clock: 400MHz (2.5ns)
*-bank:2
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: EBE10RD4ABFA-4A-E
vendor: 7F7FFE0000000000
physical id: 2
serial: 2209C4E2
slot: DIMM2_A
size: 1GiB
width: 64 bits
clock: 400MHz (2.5ns)
*-bank:3
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: HYMP512R724-E3
vendor: Hynix Semiconductor (Hyundai Electronics)
physical id: 3
serial: 00002201
slot: DIMM2_B
size: 1GiB
width: 64 bits
clock: 400MHz (2.5ns)
*-bank:4
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: 72T128000HR5A
vendor: Infineon (Siemens)
physical id: 4
serial: 011DF515
slot: DIMM3_A
size: 1GiB
width: 64 bits
clock: 400MHz (2.5ns)
*-bank:5
description: DIMM DDR2 Synchronous 400 MHz (2,5 ns)
product: M3 93T2950CZ3-CCC
vendor: Samsung
physical id: 5
serial: 46039316
slot: DIMM3_B
size: 1GiB
width: 64 bits
clock: 400MHz (2.5ns)
cat /var/log/dmesg给出这个：
[ 0.699324] pci 0000:00:06.0: PME# supported from D0 D3hot D3cold
[ 0.699331] pci 0000:00:06.0: PME# disabled
[ 0.699382] pci 0000:00:1d.0: [8086:24d2] type 0 class 0x000c03
[ 0.699431] pci 0000:00:1d.0: reg 20: [io 0xbce0-0xbcff]
[ 0.699470] pci 0000:00:1d.1: [8086:24d4] type 0 class 0x000c03
[ 0.699519] pci 0000:00:1d.1: reg 20: [io 0xbcc0-0xbcdf]
[ 0.699558] pci 0000:00:1d.2: [8086:24d7] type 0 class 0x000c03
[ 0.699607] pci 0000:00:1d.2: reg 20: [io 0xbca0-0xbcbf]
[ 0.699664] pci 0000:00:1d.7: [8086:24dd] type 0 class 0x000c03
[ 0.699690] pci 0000:00:1d.7: reg 10: [mem 0xfeb00000-0xfeb003ff]
[ 0.699783] pci 0000:00:1d.7: PME# supported from D0 D3hot D3cold
[ 0.699790] pci 0000:00:1d.7: PME# disabled
[ 0.699812] pci 0000:00:1e.0: [8086:244e] type 1 class 0x000604
[ 0.699861] pci 0000:00:1f.0: [8086:24d0] type 0 class 0x000601
[ 0.699949] pci 0000:00:1f.1: [8086:24db] type 0 class 0x000101
[ 0.699966] pci 0000:00:1f.1: reg 10: [io 0x0000-0x0007]
[ 0.699978] pci 0000:00:1f.1: reg 14: [io 0x0000-0x0003]
[ 0.700018] pci 0000:00:1f.1: reg 18: [io 0x0000-0x0007]
[ 0.700031] pci 0000:00:1f.1: reg 1c: [io 0x0000-0x0003]
[ 0.700042] pci 0000:00:1f.1: reg 20: [io 0xfc00-0xfc0f]
[ 0.700054] pci 0000:00:1f.1: reg 24: [mem 0x00000000-0x000003ff]
[ 0.700136] pci 0000:01:00.0: [8086:0330] type 1 class 0x000604
[ 0.700192] pci 0000:01:00.0: PME# supported from D0 D3hot D3cold
[ 0.700198] pci 0000:01:00.0: PME# disabled
[ 0.700230] pci 0000:01:00.2: [8086:0332] type 1 class 0x000604
[ 0.700287] pci 0000:01:00.2: PME# supported from D0 D3hot D3cold
[ 0.700292] pci 0000:01:00.2: PME# disabled
答案1
自从我安装了一个 64 位 Ubuntu 版本后，我就很难猜测我的操作系统无法检测到完整 8 GB RAM 的问题是什么（正如我所说，它只检测到 245 MB！）
由于我迫切希望找到我急需的答案，因此我决定下载 Dell PowerEdge 2850 的 PDF 手册。因此，我开始检查我在 BIOS 中看到的所有奇怪选项的含义，以及我是否将它们设置为正确的值。
当我在 PDF 文件中读到操作系统安装模式我打开的值将 RAM 限制为 256 MB。因此，我关闭了该选项并重新启动 Ubuntu。我运行了终端，很高兴free -m现在显示有 8001 MB 的可用 RAM。
所以正如我对@terdon 所说的那样，这不是与 Ubuntu 相关的问题，而是错误的 BIOS 设置。
我希望这个答案对于将来在类似服务器上遇到同样问题的人能够有所帮助。