Linux udev humor

The udev device management framework is one of the new features that was added to the Linux 2.6 kernel, and allows the /dev namespace to be populated based on hotplug events sent from the kernel to the userspace udevd daemon. While reading through the udev FAQ, I found a good explanation of udev:

Q: How is udev related to devfs?
A: udev works entirely in userspace, using hotplug events the kernel sends
   whenever a device is added or removed from the kernel. Details about
   the devices are exported by the kernel to the sysfs filesystem at /sys
   All device naming policy permission control and event handling is done in
   userspace. devfs is operated from within the kernel.

As well as some comedic writing:

Q: But udev will not automatically load a driver if a /dev node is opened
   when it is not present like devfs will do.
A: Right, but Linux is supposed to load a module when a device is discovered
   not to load a module when it's accessed.

Q: Oh come on, pretty please.  It can't be that hard to do.
A: Such a functionality isn't needed on a properly configured system. All
   devices present on the system should generate hotplug events, loading
   the appropriate driver, and udev will notice and create the
   appropriate device node.  If you don't want to keep all drivers for your
   hardware in memory, then use something else to manage your modules
   (scripts, modules.conf, etc.)  This is not a task for udev.

Q: But I love that feature of devfs, please?
A: The devfs approach caused a lot of spurious modprobe attempts as
   programs probed to see if devices were present or not.  Every probe
   attempt created a process to run modprobe, almost all of which were

This made me laugh silly, and I wish more FAQ maintainers used this style of writing. Whoever wrote this, I commend you!

1 thought on “Linux udev humor”

  1. I was wondering what udev was, as I had a system hang at that point in boot. Your post was timely for me, saved me a trip to the online dictionary. Now I have an idea of what udev is. Thanks. I learn a lot from you blog.


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