Petter Reinholdtsen

Modalias strings - a practical way to map "stuff" to hardware
14th January 2013

While looking into how to look up Debian packages based on hardware information, to find the packages that support a given piece of hardware, I refreshed my memory regarding modalias values, and decided to document the details. Here are my findings so far, also available in the Debian Edu subversion repository:

Modalias decoded

This document try to explain what the different types of modalias values stands for. It is in part based on information from <URL: >, <URL: >, <URL: > and <URL: >.

The modalias entries for a given Linux machine can be found using this shell script:

find /sys -name modalias -print0 | xargs -0 cat | sort -u

The supported modalias globs for a given kernel module can be found using modinfo:

% /sbin/modinfo psmouse | grep alias:
alias:          serio:ty05pr*id*ex*
alias:          serio:ty01pr*id*ex*

PCI subtype

A typical PCI entry can look like this. This is an Intel Host Bridge memory controller:


This represent these values:

 v   00008086  (vendor)
 d   00002770  (device)
 sv  00001028  (subvendor)
 sd  000001AD  (subdevice)
 bc  06        (bus class)
 sc  00        (bus subclass)
 i   00        (interface)

The vendor/device values are the same values outputted from 'lspci -n' as 8086:2770. The bus class/subclass is also shown by lspci as 0600. The 0600 class is a host bridge. Other useful bus values are 0300 (VGA compatible card) and 0200 (Ethernet controller).

Not sure how to figure out the interface value, nor what it means.

USB subtype

Some typical USB entries can look like this. This is an internal USB hub in a laptop:


Here is the values included in this alias:

 v    1D6B  (device vendor)
 p    0001  (device product)
 d    0206  (bcddevice)
 dc     09  (device class)
 dsc    00  (device subclass)
 dp     00  (device protocol)
 ic     09  (interface class)
 isc    00  (interface subclass)
 ip     00  (interface protocol)

The 0900 device class/subclass means hub. Some times the relevant class is in the interface class section. For a simple USB web camera, these alias entries show up:


Interface class 0E01 is video control, 0E02 is video streaming (aka camera), 0101 is audio control device and 0102 is audio streaming (aka microphone). Thus this is a camera with microphone included.

ACPI subtype

The ACPI type is used for several non-PCI/USB stuff. This is an IR receiver in a Thinkpad X40:


The values between the colons are IDs.

DMI subtype

The DMI table contain lots of information about the computer case and model. This is an entry for a IBM Thinkpad X40, fetched from /sys/devices/virtual/dmi/id/modalias:


The values present are

 bvn  IBM            (BIOS vendor)
 bvr  1UETB6WW(1.66) (BIOS version)
 bd   06/15/2005     (BIOS date)
 svn  IBM            (system vendor)
 pn   2371H4G        (product name)
 pvr  ThinkPadX40    (product version)
 rvn  IBM            (board vendor)
 rn   2371H4G        (board name)
 rvr  NotAvailable   (board version)
 cvn  IBM            (chassis vendor)
 ct   10             (chassis type)
 cvr  NotAvailable   (chassis version)

The chassis type 10 is Notebook. Other interesting values can be found in the dmidecode source:

  3 Desktop
  4 Low Profile Desktop
  5 Pizza Box
  6 Mini Tower
  7 Tower
  8 Portable
  9 Laptop
 10 Notebook
 11 Hand Held
 12 Docking Station
 13 All In One
 14 Sub Notebook
 15 Space-saving
 16 Lunch Box
 17 Main Server Chassis
 18 Expansion Chassis
 19 Sub Chassis
 20 Bus Expansion Chassis
 21 Peripheral Chassis
 22 RAID Chassis
 23 Rack Mount Chassis
 24 Sealed-case PC
 25 Multi-system
 26 CompactPCI
 27 AdvancedTCA
 28 Blade
 29 Blade Enclosing

The chassis type values are not always accurately set in the DMI table. For example my home server is a tower, but the DMI modalias claim it is a desktop.

SerIO subtype

This type is used for PS/2 mouse plugs. One example is from my test machine:


The values present are

  ty  01  (type)
  pr  00  (prototype)
  id  00  (id)
  ex  00  (extra)

This type is supported by the psmouse driver. I am not sure what the valid values are.

Other subtypes

There are heaps of other modalias subtypes according to file2alias.c. There is the rest of the list from that source: amba, ap, bcma, ccw, css, eisa, hid, i2c, ieee1394, input, ipack, isapnp, mdio, of, parisc, pcmcia, platform, scsi, sdio, spi, ssb, vio, virtio, vmbus, x86cpu and zorro. I did not spend time documenting all of these, as they do not seem relevant for my intended use with mapping hardware to packages when new stuff is inserted during run time.

Looking up kernel modules using modalias values

To check which kernel modules provide support for a given modalias, one can use the following shell script:

  for id in $(find /sys -name modalias -print0 | xargs -0 cat | sort -u); do \
    echo "$id" ; \
    /sbin/modprobe --show-depends "$id"|sed 's/^/  /' ; \

The output can look like this (only the first few entries as the list is very long on my test machine):

    insmod /lib/modules/2.6.32-5-686/kernel/drivers/acpi/ac.ko 
  FATAL: Module acpi:device: not found.
    insmod /lib/modules/2.6.32-5-686/kernel/drivers/char/nvram.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/drivers/leds/led-class.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/net/rfkill/rfkill.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/drivers/platform/x86/thinkpad_acpi.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/lib/crc-ccitt.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/net/irda/irda.ko 
    insmod /lib/modules/2.6.32-5-686/kernel/drivers/net/irda/nsc-ircc.ko 

If you want to help implementing a system to let us propose what packages to install when new hardware is plugged into a Debian machine, please send me an email or talk to me on #debian-devel.

Update 2013-01-15: Rewrite "cat $(find ...)" to "find ... -print0 | xargs -0 cat" to make sure it handle directories in /sys/ with space in them.

Tags: debian, english, isenkram.

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