thinking of updating the canonical online udev document

Robert P. J. Day rpjday at
Tue Apr 26 08:12:44 EDT 2011

  [not sure if this is the right forum for this, but i suspect others
on this list might be interested so ... there you go.]

  as part of a device driver course i may very well be teaching in the
near future (still waiting to hear), i'm thinking of adding a sizable
section on how udev works (after i figure all that out, of course.)

  currently, the canonical udev document is this one:

but as good as that doc is, it's obvious that it's getting a bit
dated.  for example, it refers to separate udev-related utilities such
as udevinfo, udevtrigger and so on when, these days, there's just
"udevadm" with the appropriate subcommand, so that's something that
could be tidied up.

  other picky things to be updated include claiming that the default
udev rules file is /etc/udev/rules.d/50-udev.rules when -- at least on
my ubuntu system -- it's /lib/udev/rules.d/50-udev-default.rules.
again, not serious, just something that could be corrected.  (mind
you, i don't know if the udev file and directory structure differs
drastically on other distros, something i'll look into.)

  and sometimes the documentation is not clear on some issues.  for
instance, are the only two possible entries for the udev.conf file


the man page for "udev" suggests that, i just wasn't sure whether
there were any other possibilities.

  finally, i was checking the default udev rules file on my ubuntu
system and, right at the top, i read:

SUBSYSTEM=="block", SYMLINK{unique}+="block/%M:%m"
SUBSYSTEM!="block", SYMLINK{unique}+="char/%M:%m"

AFAICT, there is nothing in the udev man page that explains the
"SYMLINK{unique}" notation.  it's easy enough to see how it creates
that set of symlinks based on major and minor numbers, but what's with
the "unique"?

  oh, and for this udev tutorial, i want to come up with some real,
hands-on examples, so that people can see what's happening with events
when they do stuff like insert USB keys and so on.

  anyway, this will undoubtedly take more than a few days but feel
free to use this as a thread to go through the current document, check
it against your system, post differences or updates, and i'll collect
them all and eventually write up an updated version and post it



Robert P. J. Day                                 Ottawa, Ontario, CANADA


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