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PLD udev FAQ (udev-0.71-5)

From: Fryderyk Dziarmagowski <freetz>
Subject: [FAQ] PLD udev FAQ
Date: Sun, 6 Nov 2005 21:59:31 +0100
X-Translated-By: Michał Łukaszek <prism>

Minimum recommended version is 2.6.12.x (udev hotplug won't work with the older)

Udev doesn't load all modules

That's because it loads only modules for PCI devices that meet the requirements included in udev rules. That rules allow auto-loading feature only for internal USB devices (hubs), such as uhci-hcd or ehci-hcd.

If you want to get the modules of all devices loaded automatically, enable udevsynthetize in /etc/udev/udev.conf. This is experimental and not fully tested though.

What about hotplug? Will my pendrive work?

hotplug included in current udev replaces the old hotplug completely. Parallel work of both is not recommended, so after udev is installed the old hotplug package is removed.

USB pendrives will work like a charm if you read answer no. 1.

I'd like to connect my digital camera/scanner/other USB device to my computer. Do I have to mount /proc/bus/usb with proper permissions?

Absolutely not. Install udev-digicam package, add yourself to the digicam group, and udev's agent will do the rest, no matter if the device is a scanner or another USB input device.

Can udev automatically mount partitions or cd drives it finds?

While technically possible, udev is not designed to manage your /etc/fstab entries. There are specialized programs for this, like gnome-volume-manager.

I'm using nvidia-legacy and the /dev/nvidia* is not created!

That's a problem of nvidia (legacy) drivers. udev has nothing to do with it. Unfortunately, you must manually create proper device files using mknod.

You can make modprobe create these devices for you every time the nvidia module is loaded by adding the following line to your /etc/modprobe.conf:

install nvidia /sbin/modprobe --ignore-install nvidia && { mknod /dev/nvidia0 c 195 0; mknod /dev/nvidia1 c 195 1; mknod /dev/nvidia2 c 195 2; mknod /dev/nvidia3 c 195 3; mknod /dev/nvidiactl c 195 255; /bin/true; }

Note that this should be all in one line.

Modules like psmouse and evdev are not loaded automatically

The kernel's input layer is broken. It's said to be fixed in 2.6.15.

Do I have to add the usb-controller alias in /etc/modprobe.conf?

No. All *-hcd modules are loaded automatically.

I get the error messages about failed agents in my system logs

They don't work because they are not there - unless you installed udev-digicam, which has the usb agent. That udev warnings in logs don't look nice, but they are absolutely harmless. This will be fixed if there is a person willing to fix it.

I've got a problem that is not covered here. How do I diagnose it?

Try the following:

  1. set udev_log to info in /etc/udev/udev.conf to improve verbosity of udev;
  2. use udevmonitor (see man udevmonitor) to get even more infomation from older udev;
  3. use udevadm monitor (see 'man udevadm') to get even more infomation (udev-151) ;
  4. check the linux-hotplug list's archive at

How can I increase udev logs verbosity

Try (udev-154):

udevadm control --log-priority=debug

And check results in '/var/log/daemon'

How to test rule I have just written?

Reload rules:

udevadm control --reload-rules # (udev-151)

Trigger event (replug device) or trigger all events:

udevadm trigger  --verbose 

If still unsure, ask your question on PLD mailing lists.


docs/udevfaq.txt · Last modified: 2010-06-15 21:38 by Mateusz Korniak