Change permissions on /dev file? [SOLVED ROOT ONLY XSANE execution problem]
Richard England
rengland at europa.com
Fri Apr 21 05:47:27 UTC 2006
john bray wrote:
> On Sun, 2006-01-15 at 17:05 +0100, Toralf Lund wrote:
>
>> Toralf Lund wrote:
>>
>>
>>>>>>> How can I update permissions on a device file on an FC4 setup? I
>>>>>>> mean, I know I can use chmod, of course, but the problem is that
>>>>>>> for /dev special files, the changes are lost on reboot. [ ... ]
>>>>>>>
>>>>>>
>>>>>>
>>>>>> grep -n "sg" /etc/udev/permissions.d/50-udev.permissions
>>>>>>
>>>>>>
>>>>>> The permissions are set there.
>>>>>>
>>>>>>
>>>>>>
>>>>> Right. I haven't quite got used to this new(ish) udev stuff... Seems
>>>>> to me now it must be the place for the setting I want, but the
>>>>> location you mention can't be correct for my system, as /etc/udev
>>>>> has no permissions.d.
>>>>>
>>>>>
>>>> Look to /etc/udev/rules.d
>>>> HTH
>>>>
>>> I think I should be able to define an appropriate rule for my unit,
>>> but I'm surprised to find that the udev doc does not mention a key
>>> containing the device type or vendor/product id (as reported e.g. in
>>> /proc/scsi/scsi.) Is there really now way to do direct match on those?
>>>
>> Actually, it may look like SYSFS{type} will give me what I want (for
>> device type.) I now have added
>>
>> KERNEL=="sg0", BUS=="scsi", SYSFS{type}=="6", SYMLINK="scanner", MODE="0666"
>>
>> which quite definitely has an effect, but not the one I want. In fact
>> after I did this, the device is still owned by root and accessible by
>> nobody else (i.e. has mode 0600.) Then if a user logs in via a local
>> GNOME session, owner is changed to that user, and the mode stays the
>> same. This is the same kind of behaviour as for CD-ROM, but is not right
>> in this case, as I want to share the scanner across the net (via saned
>> or just startup of the scanner software via ssh.) In fact, I'm not happy
>> with the general trend of assuming the desktop user "owns" everything,
>> as to me, flexibility in sharing resources is a very large part of what
>> Linux is or should be about.
>>
>> Anyhow, how do I get udev to actually use the mode I've told it to use???
>>
>> - Toralf
>>
>>
>>
>
> hey toralf -
>
> i had that same frustration. i was sure that udev wasn't properly
> setting the permissions. but...
>
> i suspect that udev is doing the proper permissions. what you are
> seeing is the result of the pam security stuff
> in /etc/security/console.perms.d
>
> when a user logs in, the devices controlled by that system, have their
> owners and permissions changed as specified.
>
> i just finished putting up a file in that directory called local.perms
> because of scanner problems here. the scanner part is:
>
> <scanner>=/dev/scanner* /dev/usb/scanner* /dev/sg*
>
> # permission definitions
>
> <console> 0666 <scanner> 0666 root
>
> i'm not yet sure that the /dev/sg* part is necessary. note that 666 may
> not be what you want. but, i sometimes su to other users for testing
> and its more convenient for me.
>
> you can use udevstart to rescan for devices and it appears to also force
> the console/pam stuff to re-do things as well.
>
> it appears that the perms files need to be named the reverse of the udev
> rules files. as i currently understand it, with the perms files, the
> last one read is the winner. but, with udev, it seems to be the case
> that the first one found is the winner. so, my local udev rules are
> named 10-local.rules but, my local console perms file is named
> local.perms, so it gets parsed after the 50-* file does.
>
> still in the process, so YMMV.
>
> john
>
>
This may be ancient history but I don't believe I ever saw a follow-up
to this.
I followed your instructions, John, and after a logout/login the
permissions on my scanner were opened to all my users.
Thanks for sharing this information.
--
--R
------------------------------------------------------------------------
/Linux, and Open Software, an alternative./
Registered Unix <http://counter.li.org> user #409453
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