Memory size and Memory location in Linux

Quick easy post: I right now need to find (I am tying this as I am solving the problem, so this will be a rough post) how many memory slots the motherboard of a machine running Linux (actually Xenserver, but close enough for our needs) has, which ones are being occupied, and which kind of SIMM cards it is using. This machine is in a server room about a mil from me am I do not want to go face the rain to get there. So, how to do the deed?

The Xencenter interface does not seem to be helpful with that, so we will don our battle moustaches (ladies, it is ok to buy a nice handlebar moustache to use in this occasions; the look of your coworkers should be reason enough to do it) and go to command line.

The command in question is dmidecode, which can be found in most Linux distros to probulate the system management BIOS. Some of you have used it before, so let's rush through it a bit. This is how it starts:

# dmidecode 2.11
SMBIOS 2.7 present.
77 structures occupying 4848 bytes.
Table at 0xCF42C000.

Handle 0xDA00, DMI type 218, 11 bytes
OEM-specific Type
        Header and Data:
                DA 0B 00 DA B2 00 17 20 0E 10 01

Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
        Vendor: Dell Inc.
        Version: 2.3.3
        Release Date: 07/10/2014
        Address: 0xF0000
        Runtime Size: 64 kB
        ROM Size: 8192 kB
        Characteristics:
                ISA is supported
                PCI is supported
                PNP is supported
                BIOS is upgradeable
                BIOS shadowing is allowed
                Boot from CD is supported
                Selectable boot is supported
                EDD is supported
                Japanese floppy for Toshiba 1.2 MB is supported (int 13h)
                5.25"/360 kB floppy services are supported (int 13h)
                5.25"/1.2 MB floppy services are supported (int 13h)
                3.5"/720 kB floppy services are supported (int 13h)
                8042 keyboard services are supported (int 9h)
                Serial services are supported (int 14h)
                CGA/mono video services are supported (int 10h)
                ACPI is supported
                USB legacy is supported
                BIOS boot specification is supported
                Function key-initiated network boot is supported
                Targeted content distribution is supported
                UEFI is supported
        BIOS Revision: 2.3

As you can see, the machine in question is a Dell (they do make servers you know; this one is a 1U) and we can see some of its specs. Next would be stuff like CPU specs (cache, features, speed), which we don't care right now. What we care about is the memory:

Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 16384 MB
        Form Factor: DIMM
        Set: 1
        Locator: DIMM_A1
        Bank Locator: Not Specified
        Type: DDR3
        Type Detail: Synchronous Registered (Buffered)
        Speed: 1600 MHz
        Manufacturer: 00CE00B300CE
        Serial Number: 0296F2E0
        Asset Tag: 01150664
        Part Number: M393B2G70EB0-YK0
        Rank: 2
        Configured Clock Speed: 1333 MHz

Handle 0x1101, DMI type 17, 34 bytes
Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 16384 MB
        Form Factor: DIMM
        Set: 1
        Locator: DIMM_A2
        Bank Locator: Not Specified
        Type: DDR3
        Type Detail: Synchronous Registered (Buffered)
        Speed: 1600 MHz
        Manufacturer: 00CE00B300CE
        Serial Number: 0296F43E
        Asset Tag: 01150664
        Part Number: M393B2G70EB0-YK0
        Rank: 2
        Configured Clock Speed: 1333 MHz

Handle 0x1102, DMI type 17, 34 bytes
Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: No Module Installed
        Form Factor: DIMM
        Set: 2
        Locator: DIMM_A3
        Bank Locator: Not Specified
        Type: DDR3
        Type Detail: Synchronous
        Speed: Unknown
        Manufacturer:
        Serial Number:
        Asset Tag:
        Part Number:
        Rank: Unknown
        Configured Clock Speed: Unknown

Handle 0x1103, DMI type 17, 34 bytes
Memory Device
[...]

As you can see, we have a 16GB SIMM (fine, be grammar police and call it a DIMM) on DIMM_A1 amd DIMM_A2 slots, but nobody on DIMM_A3; just between us, this machine only has those 2 SIMMs. So, how about we find out how many SIMM slots this machine have?

[root@vmhost3 ~]# dmidecode | grep 'Locator: DIMM_'
        Locator: DIMM_A1
        Locator: DIMM_A2
        Locator: DIMM_A3
        Locator: DIMM_A4
        Locator: DIMM_A5
        Locator: DIMM_A6
[root@vmhost3 ~]#

Hmm, we can do better; let's be lazy and let the script do the count. And, just to show we are good, we will use sed instead of grep because the name is shorter

[root@vmhost3 ~]# dmidecode | sed -n '/Locator: DIMM_/p'|wc -l
6
[root@vmhost3 ~]#

Six slots. Not bad. So, how many of those are being populated? We know that an empty slot is flagged by Size: No Module Installed. Let's then look for the entries without that pattern, which is easy to do using grep:

[root@vmhost3 ~]# dmidecode | grep -A5 'Memory Device' | grep -c 'MB'
2
[root@vmhost3 ~]#

Note we dropped the wc since grep can count how many times we got successful matches. Also, the -A5 means that we are printing the first 5 lines after the matched pattern; this way the second grep has something to bite. How about if we spit out the name of which memory slots have memory and how big they are? And maybe the type and model number while we are at it. Here's how to do the deed using grep:

[root@vmhost3 ~]# dmidecode |  grep -A18  'Memory Device' | grep -B4 -A13 -e 'Size:.* MB' | grep -e 'Locator: D' -e 'Size' -e 'Part Number'
        Size: 16384 MB
        Locator: DIMM_A1
        Part Number: M393B2G70EB0-YK0
        Size: 16384 MB
        Locator: DIMM_A2
        Part Number: M393B2G70EB0-YK0
[root@vmhost3 ~]# 

I used 3 greps here to make it easier to see what is going on:

1. Fist grep finds from the dmidecode output the entries related to memories and feed the complete entry (each is 18 lines long) to the next grep.
   
2. This one then only looks for entries that have memories being reported in megabytes (MB); the fragile assumption here is that if there is a SIMM in the slot, its Size: will be reported as X MB, otherwise as we found out above it will be Size: No Module Installed. The cleverest way to do this is to test for Size: No Module Installed; if it is not there use it. But, I never claimed to be that clever.

   Now, if a matching pattern is found, we print the entire entry for this memory device, hence the -A13 (after) and -B4 (before); they print the lines before and after the one which contains the pattern.
   

3. Finally we print only the lines we want to use, namely Part Number, Size, and Locator(which SIMM slot memory is sitting on).

Now, I know how many memory slots are available, which ones are being occupied, and which memory card models are installed. I can now decide if I want to buy more matching ones or lookup the specs and find the largest cards that will work in this device. Not bad for a rainy day.