[Tfug] Re: 2.6 hangs on "Discovering hardware:"

[John Gruenenfelder]

On Fri, Jul 01, 2005 at 12:28:29AM -0700, t takahashi wrote:
>in case somebody is interested in this (if nobody is, sorry for the
>list pollution), here is what i did to partially fix it.
>
>remove discover
>  gets past discovering hardware now
>  seems to be only nec for x configuration
>unplug usb hub
>  gets past hotplug now and boots
>
>i'm going to remove hotplug and udev, since i don't recall why i need
>them anyway, then plug in the hub and see if it works.
>
>still don't know what caused the problem, or whether other ide stuff
>will work, but /dev/dsp exists now.

hotplug is usually pretty important on most newer Linux systems.  Hotplug
handles the automatic loading of modules when you install new hardware while
the machine is running, such as a USB mouse or similar.  Hotplug also scans
your system at boot to load the necessary modules for the currently installed
hardware.  Without hotplug, you'll need to make sure you manually load all of
those yourself.

discover performs a similar task, but, if I recall correctly, does not rely on
the hotplug interface in the kernel.  I have always found it to be both slow
and redundant when hotplug is present.  I just get rid of it and rely on
hotplug.

udev may or may not be important depending on how your system is set up.  udev
is the successor to the 2.4 kernel's devfs system, but it's all userspace and
more powerful.  When udev starts, it mounts *over* your regular /dev directory
with a tmpfs filesystem.  udev then populates this new /dev with device
entries for only the hardware you have installed.  I personally like this,
though many still prefer the older static /dev setup.

Once nice feature of udev (or devfs before it) is that it works in conjunction
with hotplug to create new device entries on the fly.  So, for example, I can
plug in my USB memory card reader.  When I do so, /dev/sdb and /dev/sdb1 will
show up.  udev also means that you no longer have to create /dev entries.  The
drivers will all handle it for you.


-- 
--John Gruenenfelder    Research Assistant, Steward Observatory, U of Arizona
                        johng at as.arizona.edu
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