Change permissions on /dev file? [SOLVED ROOT ONLY XSANE execution problem]

Richard England rengland at europa.com
Fri Apr 21 05:58:18 UTC 2006


Richard England wrote:
> 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.
>
Arghh.  Spoke too soon.  I can, indeed, get xsane to come up as a user 
or as root, but neither of them will scan.  I get a "device busy" 
warning box and no scanning.  Back to google.

FYI,  Canon LiDE 50  (USB scanner) on Fedora 5 full updates (at the moment).


-- 
--R
------------------------------------------------------------------------
/Linux, and Open Software, an alternative./
Registered Unix <http://counter.li.org> user #409453




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