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= General notes =

 * The default names for devices come from the kernel.

 * Our naming policy is to follow the standard `devices.txt` suggested names, applying them where the kernel driver uses a mnemonic name.

 * We do not supply special names, no, you cannot have `/dev/pony`.

 * However if ponies are a class of devices that share a common subsystem or driver, and are commonly addressed in this way, you could have `/dev/pony0`...`/dev/ponyN`

 * The numbers on the end of the enumerated devices are assigned by the kernel on a first-come, first-served basis.

 * This means every time you boot, the numbers swap around.

 * This is not a bug.

 * We counter the above by creating symlinks with device-unique names (serial numbers, UUIDs, etc.) e.g. `/dev/disk/by-uuid` and `/dev/input/by-id`

 * udev does not mount your disks, HAL, gnome-volume-manager and pmount do that.

 * udev doesn't pick which module gets loaded, modprobe does that.

= Common symptoms =

 * `/dev/null` with wrong permissions: udev failed to start in the real filesystem, make sure that the udevd from the initramfs was killed, and that there is only one udev startup script.

 * 3-minute hang on boot: one of the devices rules is failing, check `/var/log/udev` as noted below.
  * often this is ifup, hdparm, etc.

= Useful things =

 * `sudo udevadm monitor -e` ... this should be run for any problems when a device is plugged in, or removed.  It will output UEVENT blocks for the event from the kernel, and a following UDEV block; these are timestamped so you know how long it takes to process.  The UDEV block contains more information, which udev adds through various helper programs.

 * `/var/log/udev`, this is the output from above for the boot process.  Especially note whether a UDEV block takes a long amount of time to appear, or doesn't appear at all.

 * To see the actions udevd is taking, you can run it in verbose debug mode:
  * sudo pkill udevd
  * sudo udevd --debug-trace --verbose --suppress-syslog
 * To get more debug info from udev,
  * edit /usr/share/initramfs-tools/scripts/init-top/udev, and change the line starting udev by adding --debug, removing --daemon (using & instead), and sending stdout and stderr into a file called /dev/.udev.debug . For instance:

    /sbin/udevd --debug --resolve-names=never > /dev/.udev.debug 2>&1 &
  * then run sudo update-initramfs -k all -u
  * After reboot, /dev/.udev.debug will have the udev debug info.


= Known bugs =

Description of known issues, how to recognise them and stock responses/actions.

'''Open'''
||<rowbgcolor="#eeeeee"> '''Bug#''' || '''Description''' || '''Action''' ||
|| TBD. || TBD. || TBD. ||

'''Closed'''
||<rowbgcolor="#eeeeee"> '''Bug#''' || '''Description''' || '''Action''' ||
|| TBD. || TBD. || TBD. ||

= Non-bugs =

TBD.

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CategoryBugSquad CategoryDebugging