Memory missing:: Warning only 4GB will be used. Use a PAE enabled kernel

Question

One of our servers has been setup with 8G ram. But its showing only 3.2G. Pasting the info for further analysis.

=========

[root@s209 ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          3289        879       2409          0         37        669
-/+ buffers/cache:        173       3115
Swap:         4094          0       4094
[root@s209 ~]#

[root@s209 ~]# cat /proc/meminfo
MemTotal:      3368192 kB
MemFree:       2482456 kB
Buffers:         38144 kB
Cached:         685216 kB
SwapCached:          0 kB
Active:         413112 kB
Inactive:       435088 kB
HighTotal:     2488768 kB
HighFree:      1669300 kB
LowTotal:       879424 kB
LowFree:        813156 kB
SwapTotal:     4192956 kB
SwapFree:      4192956 kB
Dirty:            1596 kB
Writeback:           0 kB
AnonPages:      124788 kB
Mapped:          17104 kB
Slab:            24928 kB
PageTables:       3840 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   5877052 kB
Committed_AS:   389964 kB
VmallocTotal:   114680 kB
VmallocUsed:      5536 kB
VmallocChunk:   109028 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     4096 kB

=========

[root@s209 ~]# uname -r
2.6.18-194.el5

=========

=========

[root@s209 ~]# dmesg | less 

Linux version 2.6.18-194.el5 (mockbuild@builder16.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Fri Apr 2 14:58:35 EDT 2010
BIOS-provided physical RAM map:
 BIOS-e820: 0000000000010000 - 000000000009dc00 (usable)
 BIOS-e820: 000000000009dc00 - 00000000000a0000 (reserved)
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
 BIOS-e820: 0000000000100000 - 00000000cfe70000 (usable)
 BIOS-e820: 00000000cfe70000 - 00000000cfe7d000 (ACPI data)
 BIOS-e820: 00000000cfe7d000 - 00000000cfe80000 (ACPI NVS)
 BIOS-e820: 00000000cfe80000 - 00000000d0000000 (reserved)
 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
 BIOS-e820: 00000000fec00000 - 00000000fed00000 (reserved)
 BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
 BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
 BIOS-e820: 0000000100000000 - 0000000230000000 (usable)
Warning only 4GB will be used.
Use a PAE enabled kernel.
3200MB HIGHMEM available.
896MB LOWMEM available.

=========

=========

[root@s209 ~]# dmidecode -t 17
# dmidecode 2.10
SMBIOS 2.5 present.

Handle 0x0013, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0012
        Error Information Handle: No Error
        Total Width: 40968 bits
        Data Width: 41024 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: 1
        Locator: J6G1
        Bank Locator: DIMM 0
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: Hyundai Electronics
        Serial Number: 4121C2C5
        Asset Tag: 41410933
        Part Number: 48594D503132355536344350382D53362020

Handle 0x0014, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0012
        Error Information Handle: No Error
        Total Width: 41480 bits
        Data Width: 41536 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: 1
        Locator: J6G2
        Bank Locator: DIMM 1
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: Unknown
        Serial Number: 00000000
        Asset Tag: 00000000
        Part Number: 000000000000000000000000000000000000

Handle 0x0015, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0012
        Error Information Handle: No Error
        Total Width: 41992 bits
        Data Width: 42048 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: 1
        Locator: J6H1
        Bank Locator: DIMM 2
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: Princeton Technology
        Serial Number: 100916C6
        Asset Tag: 00000A37
        Part Number: 5052494E4345544F4E000000000000000000

Handle 0x0016, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0012
        Error Information Handle: No Error
        Total Width: 42504 bits
        Data Width: 42560 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: 1
        Locator: J6H2
        Bank Locator: DIMM 3
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: Unknown
        Serial Number: 00000000
        Asset Tag: 00000000
        Part Number: 000000000000000000000000000000000000

=========

Any help to resolve this issue will be very helpful.

Sincerely, Ajo

Answer 1

If you run uname -a, chances are you'll see you're running a 32-bit kernel. PAE (Physical Address Extension) allows the kernel to expand the amount of memory that you can address to reach larger numbers.

You'll need to switch to a PAE-enabled Kernel. You can recompile, or... yum install kernel-pae and switch to boot from that kernel.

Good luck!

Answer 2

You are almost certainly running a 32-bit kernel as Redmumba suggests.

As well as the PAE option, you can also run a 64-bit kernel with a 32-bit userland happily - this has a similar effect to PAE in that the system overall can use the 64-bit address-space but individual processes (unless they are explicitly PAE aware) are limimed to a 32-bit address space. IIRC the context switching between a 64-bit kernal and 32-bit processes imposes less of a bottle-neck than PAE so you might find this option more efficient. I don't know about CentOS, but with Debian you can just run aptitude install linux-image-amd64 (note from http://packages.debian.org/squeeze/linux-image-amd64 that this virtual package and its dependencies exist for both the amd64 and i386 builds) and it will do the work for you (and automatic updates will come through fine as you have not hand-compile anything rather than using the package management system).

If this is a brand new setup (i.e. the OS has only just been installed rather than you've just upgraded the RAM on an existing server) then I would suggest a full reinstall using a fully 64-bit setup (both userland and kernel).

Answer 3

Yes, the os is 32 bit.

Linux s209.xxxxx.net 2.6.18-194.el5 #1 SMP Fri Apr 2 14:58:35 EDT 2010 i686 i686 i386 GNU/Linux