dmidecode - DMI table decoder
is a tool for dumping a computer's DMI (some say SMBIOS) table
contents in a human-readable format. This table contains a description of the
system's 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 doesn't 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. It will first
try to read the DMI table from sysfs, and next try reading directly from
memory if sysfs access failed. If dmidecode
succeeds in locating a
valid DMI table, 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 doesn't 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 displayed value.
- Decoded values. The information presented of course depends
on the type of record. Here, we learn about the board's manufacturer,
model, version and serial number.
- -d, --dev-mem FILE
- Read memory from device FILE (default:
- -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, bios-version, bios-release-date,
system-version, system-serial-number, system-uuid,
chassis-type, chassis-version, chassis-serial-number,
processor-frequency. 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.
Note: on Linux, most of these strings can alternatively be read directly
from sysfs, typically from files under
/sys/devices/virtual/dmi/id. Most of these files are even readable
by regular users.
- -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
- --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 FILE
- Read the DMI data from a binary file previously generated
- Do not attempt to read DMI data from sysfs files. This is
mainly useful for debugging.
- --oem-string N
- Only display the value of the OEM string number N.
The first OEM string has number 1. With special value "count",
return the number of OEM strings instead.
- -h, --help
- Display usage information and exit
- -V, --version
- Display the version and exit
Options --string, --type, --dump-bin and --oem-string determine the output
format and are mutually exclusive.
Please note in case of dmidecode
is run on a system with BIOS that boasts
new SMBIOS specification, which is not supported by the tool yet, it will
print out relevant message in addition to requested data on the very top of
the output. Thus informs the output data is not reliable.
The SMBIOS specification defines the following DMI types:
||On Board Devices
||System Configuration Options
||System Event Log
||Physical Memory Array
||32-bit Memory Error
||Memory Array Mapped Address
||Memory Device Mapped Address
||Built-in Pointing Device
||System Power Controls
||Electrical Current Probe
||Out-of-band Remote Access
||Boot Integrity Services
||64-bit Memory Error
||Management Device Component
||Management Device Threshold Data
||Onboard Devices Extended Information
||Management Controller Host Interface
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.
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:
||1, 12, 15, 23, 32
||2, 10, 41
||5, 6, 16, 17
Keywords are matched case-insensitively. The following command lines are
- dmidecode --type 0 --type 13
- dmidecode --type 0,13
- dmidecode --type bios
- dmidecode --type BIOS
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.
/dev/mem /sys/firmware/dmi/tables/smbios_entry_point (Linux only)
/sys/firmware/dmi/tables/DMI (Linux only)
- 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