dmidecode - Unix, Linux Command
dmidecode - DMI table decoder
dmidecode is a tool for dumping a computers DMI (some say SMBIOS) table
contents in a human-readable format. This table contains a description of the
systems hardware components, as well as other useful pieces of information
such as serial numbers and BIOS revision. Thanks to this table, you can
retrieve this information without having to probe for the actual hardware.
While this is a good point in terms of report speed and safeness, this also
makes the presented information possibly unreliable.
The DMI table doesnt only describe what the system is currently made
of, it also can report the possible evolutions (such as the fastest supported
CPU or the maximal amount of memory supported).
SMBIOS stands for System Management BIOS, while DMI
stands for Desktop Management Interface. Both standards are tightly related
and developed by the DMTF (Desktop Management Task Force).
As you run it,
dmidecode will try to locate the DMI table. If it succeeds, it will then parse
this table and display a list of records like this one:
Handle 0x0002, DMI type 2, 8 bytes.
Base Board Information
Product Name: C440GX+
Serial Number: INCY92700942
Each record has:
A handle. This is a unique identifier, which allows records to
reference each other. For example, processor records usually reference
cache memory records using their handles.
A type. The SMBIOS specification defines different types of elements
a computer can be made of. In this example, the type is 2, which
means that the record contains "Base Board Information".
A size. Each record has a 4-byte header (2 for the handle, 1 for the type,
1 for the size), the rest is used by the record data. This value doesnt
take text strings into account (these are placed at the end of the record),
so the actual length of the record may be (and is often) greater than the
Decoded values. The information presented of course depends on the type
of record. Here, we learn about the boards manufacturer, model, version
and serial number.
Options --string, --type and --dump-bin
determine the output format and are mutually exclusive.
-d, --dev-mem FILE |
Read memory from device FILE (default: /dev/mem)
-q, --quiet |
Be less verbose. Unknown, inactive and OEM-specific entries are not
displayed. Meta-data and handle references are hidden.
-s, --string KEYWORD |
Only display the value of the DMI string identified by KEYWORD.
KEYWORD must be a keyword from the following list: bios-vendor,
Each keyword corresponds to a given DMI type and a given offset
within this entry type.
Not all strings may be meaningful or even defined on all systems. Some
keywords may return more than one result on some systems (e.g.
processor-version on a multi-processor system).
If KEYWORD is not provided or not valid, a list of all valid
keywords is printed and
dmidecode exits with an error.
This option cannot be used more than once.
-t, --type TYPE |
Only display the entries of type TYPE. TYPE can be either a
DMI type number, or a comma-separated list of type numbers, or a
keyword from the following list: bios, system,
baseboard, chassis, processor, memory,
cache, connector, slot. Refer to the DMI TYPES section
below for details.
If this option is used more than once, the set of displayed entries will be
the union of all the given types.
If TYPE is not provided or not valid, a list of all valid keywords
is printed and
dmidecode exits with an error.
-u, --dump |
Do not decode the entries, dump their contents as hexadecimal instead.
Note that this is still a text output, no binary data will be thrown upon
you. The strings attached to each entry are displayed as both
hexadecimal and ASCII. This option is mainly useful for debugging.
--dump-bin FILE |
Do not decode the entries, instead dump the DMI data to a file in binary
form. The generated file is suitable to pass to --from-dump
--from-dump FILE |
Read the DMI data from a binary file previously generated using
-h, --help |
Display usage information and exit
-V, --version |
Display the version and exit
The SMBIOS specification defines the following DMI types:
|10||On Board Devices|
|12||System Configuration Options|
|15||System Event Log|
|16||Physical Memory Array|
|18||32-bit Memory Error|
|19||Memory Array Mapped Address|
|20||Memory Device Mapped Address|
|21||Built-in Pointing Device|
|25||System Power Controls|
|29||Electrical Current Probe|
|30||Out-of-band Remote Access|
|31||Boot Integrity Services|
|33||64-bit Memory Error|
|35||Management Device Component|
|36||Management Device Threshold Data|
Additionally, type 126 is used for disabled entries and type 127 is an
end-of-table marker. Types 128 to 255 are for OEM-specific data.
dmidecode will display these entries by default, but it can only decode them
when the vendors have contributed documentation or code for them.
Keywords can be used instead of type numbers with --type.
Each keyword is equivalent to a list of type numbers:
|system||1, 12, 15, 23, 32|
|baseboard||2, 10, 41|
|memory||5, 6, 16, 17|
Keywords are matched case-insensitively. The following command lines are equivalent:
dmidecode --type 0 --type 13
dmidecode --type 0,13
dmidecode --type bios
dmidecode --type BIOS
BINARY DUMP FILE FORMAT
The binary dump files generated by --dump-bin and read using --from-dump
are formatted as follows:
The SMBIOS or DMI entry point is located at offset 0x00.
It is crafted to hard-code the table address at offset 0x20.
The DMI table is located at offset 0x20.
More often than not, information contained in the DMI tables is inaccurate,
incomplete or simply wrong.
Alan Cox, Jean Delvare