| | Deconstructing Linux ``udev`` Rules |
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| | =================================== |
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| | ``udev`` is one of those pieces of ``Linux`` that is fairly well |
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| | documented and not very well understood. This note isn't intended as |
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| | a general introduction to writing ``udev`` rules, but, rather, a brief |
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| | introduction to the topic by way of specific example. |
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| | Why Bother With ``udev``? |
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| | ========================= |
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| | There are many clever uses for ``udev`` documented on the Web, but |
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| | the most common use is to ensure that when you connect a device |
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| | - disk, tape, usb thumbdrive, camera... whatever - to a ``Linux`` |
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| | system, that device shows up with the same name every time. |
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| | Original ``Unix`` derivatives had a static tree of devices the system |
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| | could support. This was encoded in the ``/dev`` file tree hierarchy. |
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| | This was pretty inflexible in the face of devices being added- and |
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| | removed- from the system as it ran. For this reason, modern device |
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| | handling in ``Linux`` and most other ``Unix`` derivatives is |
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| | *dynamic* - the content of ``/dev`` changes to reflect the actual |
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| | state of the system as things get connected or disconnected. (Exactly |
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| | how this is done is outside the purpose of this document, but if you |
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| | care, investigate the ``Linux /sys`` filesystem works.) |
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| | Our Example Problem |
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| | =================== |
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| | While the example below is "cooked", it is very much rooted in real |
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| | world ``udev`` application. We want to do the following things: |
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| | - Make sure that a particular disk always shows up under the same |
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| | name under ``/dev`` no matter how many disks have been connected |
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| | before it. We do that by uniquely identifying a disk and then |
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| | creating a symbolic link to it that never changes. |
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| | - Change the user and group ownership of that disk to something |
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| | other than the default of ``root:disk``. |
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| | - Create a corresponding "raw" character device under ``/dev/raw``. |
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| | This is something you commonly see on database servers and |
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| | it's suffiently useful that's it's worth mentioning here. |
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| | Where Do ``udev`` Rules Live? |
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| | ============================= |
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| | Our Example Rules |
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| | ================= |
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| | Author |
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| | ====== |
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| | Document Revision Information |
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| | ============================= |
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| | |
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| | ``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.100 2013/10/31 21:05:37 tundra Exp $`` |
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| | ``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.101 2013/10/31 21:40:42 tundra Exp $`` |
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| | You can find the latest version of this document at: |
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| | http://www.tundraware.com/TechnicalNotes/Deconstructing-Linux-udev-Rules |
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tundra
authored
on 31 Oct 2013