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README-hwprobe.md

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hwprobe environment variable/kernel cmdline parameter

This document describes the hwprobe environment variable/kernel cmdline parameter.

You can control the hardware probing using the environment variable hwprobe and the kernel cmdline parameter hwprobe.

If hwprobe is set on the kernel cmdline, the environment variable hwprobe is ignored. Otherwise, the meaning of both is exactly the same.

Controlling probing flags

hwprobe controls which probing flags should always be set/cleared (These settings cannot be overridden by command line switches). Examples:

  • hwprobe=-isapnp - never do any isapnp probing
  • hwprobe=-braille,-modem - don't look for braille displays & modems

The list of supported flags varies from version to version. To get a list of the actual set of probing flags, call hwinfo -all (Not --all!) and look at the top of the log (it lists all probing flags with their respective status there).

Adding/removing hardware from results

hwprobe allows you to add and remove hardware from the probing results. In this case the syntax is (-: remove, +: add at end of list, <nothing>: add at begin of list):

hwprobe=[+-]<device_class>:<vendor_id>:<device_id>[:<unix_device_file>]

<device_class>, <vendor_id> and <device_id> are device ids as used by libhd. See the output of hwinfo for examples. In connection with -, you can use * as a placeholder that matches every id.

Note: <unix_device_file> is optional.

Note2: you cannot usefully add hardware that needs more info than that given by the hwprobe entry. Disks & floppies are notable examples. (But you can remove them.)

Here is a typical hwinfo output for a mouse, with the relevant ids underlined (<device_class> is the combined base_class & sub_class), (see 1st example below):

    14: PS/2 00.0: 10500 PS/2 Mouse
                   ^^^^^ -->	<device_class>
      [Created at mouse.110]
      Vendor: s0200 "Unknown"
              ^^^^^  -->		<vendor_id>
      Model: 0002 "Generic PS/2 Mouse"
             ^^^^  -->		<device_id>
      Device File: /dev/psaux
                   ^^^^^^^^^^ -->	<unix_device_file>
      Driver Info #0:
        XFree86 Protocol: ps/2
        GPM Protocol: ps2
      Attached to: #8 (PS/2 Controller)

Examples:

    hwprobe=+10500:s200:2:/dev/psaux
      o add a ps/2 mouse [at the end of the hardware list]

    hwprobe=10500:s200:2:/dev/psaux
      o add a ps/2 mouse [at the start of the hardware list, so it
        is our default mouse]

    hwprobe=+10b00:s5001:0:/dev/ttyS0
      o add a braille display connected to /dev/ttyS0

    hwprobe=-10500:s200:2:/dev/psaux
      o remove ps/2 mice attached to /dev/psaux

    hwprobe=-10500:s200:2
      o remove all ps/2 mice

    hwprobe=-10500:*:*
      o remove all ps/2 mice

    hwprobe=-*:*:*:/dev/hdc
      o remove /dev/hdc

    hwprobe=+401:1274:5000
      o add an ensoniq sound card

Graphics cards are slightly trickier:

    hwprobe=+300:1014:b7
      o add a Fire GL1 card
        Note: this way you'll get a multihead config. You'll probably
        rather want the following example.

    hwprobe=-300:*:*,+300:1014:b7
      o remove all graphics cards; then add a Fire GL1 card

    hwprobe=+400:121a:1
      o add a 3fx voodoo card (Note the class "400", not "300"!)

For more ids, see src/ids/names.* and src/ids/drivers.*.