Slackware 10.2 Where is udevd started?

rwcooper · 04-05-2006, 08:16 PM

Hi,

I'm running slackware 10.2 with the generic 2.6.13 kernel. udevd is running even though /etc/rc.d/rc.udev does not have execute permission. Doing a grep on /etc for udev doesn't show any other script attemping to execute udevd.

If anyone can tell me where udevd is getting started I would appreciate it.

Thanks,
Randy

Randux · 04-06-2006, 12:56 PM

There's something going on in rc.S but I don't understand what it's doing.

imitheos · 04-06-2006, 05:11 PM

Quote:

Originally Posted by Randux

There's something going on in rc.S but I don't understand what it's doing.

Do you mean this ?

Code:

# Initialize udev to manage /dev entries for 2.6.x kernels:
if [ -x /etc/rc.d/rc.udev ]; then
  if ! grep -w nohotplug /proc/cmdline 1> /dev/null 2> /dev/null ; then
    /etc/rc.d/rc.udev
  fi
fi

This doesn't start udevd. It starts the rc.udev script but in rwcooper's case it isn't executed since rc.udev doesn't
have execute permission.

In older udev releases (the one that slackware uses), udev was called from the hotplug subsystem. That is, when you
plug a usb flash disk, the hotplug insmoded the driver and udev mknoded the device. udevd is called when needed by
udevsend.

In newer udev releases this is deprecated and all the work is done by udevd.

I can't say for sure that this is your case, but it a possible cause.

Try "cat /proc/sys/kernel/hotplug" and see if it has some value like "/sbin/hotplug" or something else.
what permission does /etc/rc.d/rc.hotplug have ?
If you see in /etc/hotplug.d/default you will see 10-udev.hotplud which is called in order for the device to be made
according to the procedure i described above.

If the thing i describe is the cause for udevd being loaded (most probably is), you can try one of the following
1) echo "/dev/null" > /proc/sys/kernel/hotplug
2) rm /etc/hotplug.d/default/10-udev.hotplug

Try it and see if it works.

Randux · 04-07-2006, 12:05 AM

I thought it might be a kernel module but I didn't find it in rc.modules either.......

Maybe if he doesn't want it he can put it in blacklist.

rwcooper · 04-07-2006, 08:59 AM

Hi,

Thanks for the info. At this point I'm not concerned that udevd is running. I simply wanted to know where it is being started, and if necessary how to stop it from running. Allthough at this time I don't know why I might want to stop it.

Randy

Randux · 04-07-2006, 09:08 AM

I think it's a good question, but I think I also read that udev was the default in Slackware's 2.6 kernels...it may not be script-related. Maybe some of the guys running Slack with 2.6 can tell us.

imitheos · 04-08-2006, 10:07 AM

Quote:

Originally Posted by Randux

I thought it might be a kernel module but I didn't find it in rc.modules either.......

Maybe if he doesn't want it he can put it in blacklist.

udev doesn't have any kernel module. It is pure userspace. devfs was kernelspace.

Quote:

Originally Posted by Randux

I think it's a good question, but I think I also read that udev was the default in Slackware's 2.6 kernels...it may not be script-related. Maybe some of the guys running Slack with 2.6 can tell us.

I believe that it is script related. that is udevd is started from a script. I have explained in my previous post but
let me explain it more thoroughly. I may be wrong of course but i believe this is the reason that it is started.

a)You plug a device (i.e a usb flash disk).
b) The kernel runs the program that is mentioned in /proc/sys/kernel/hotplug (i think /sbin/hotplug in older kernels and
udevsend in newer ones) in order for the proper driver to be hotloaded

c) /sbin/hotplug runs its rules programs which reside in /etc/hotplug.d/default in alphabetical order.
By default there are 2 programs.

Code:

bash-3.1$ ls -l /etc/hotplug.d/default/
lrwxrwxrwx 1 root root   14 2006-01-03 11:56 10-udev.hotplug -> /sbin/udevsend
-rwxr-xr-x 1 root root 2931 2004-09-21 00:40 default.hotplug

1 is before d, so udevsend is run first so that the device is made and then default.hotplug is run which loads the
appropriate driver.
d) So, until now we said that udevsend is run to send the events.
I quote from the udevsend manpage

Quote:

udevd allows the serialization of hotplug(8) events. The events gener-
ated by the kernel may arrive in random order in userspace, that makes
it neccessary to reorder them.
... blah ...
udevd receives the events from udevsend If udevd isn't already running,
udevsend will start it.

So, udevsend which was called from the hotplug subsystem ran udevd.

As i said, i may be wrong but it the most possible cause of udevd being run.