[gentoo-user] Permissions of files in /sys/

[gentoo-user] Permissions of files in /sys/

[Momesso Andrea]

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I'd like to make the file /sys/class/backlight/asus-laptop/brightness
writeable for users, so that I don't need to be root anymore to change
the brightness.

Of course I can chown or chmod ot in local.start but I'm asking if there
is a cleaner way.

Also, are there any security risks on changing permissions on /sys
files?


TopperH

===========================
Momesso Andrea
http://topperh.blogspot.com
===========================

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Re: [gentoo-user] Permissions of files in /sys/

[Dale]

Momesso Andrea wrote:
> I'd like to make the file /sys/class/backlight/asus-laptop/brightness
> writeable for users, so that I don't need to be root anymore to change
> the brightness.
>
> Of course I can chown or chmod ot in local.start but I'm asking if there
> is a cleaner way.
>
> Also, are there any security risks on changing permissions on /sys
> files?
>
>
> TopperH
>
> ===========================
> Momesso Andrea
> http://topperh.blogspot.com
> ===========================
>   

I have never did this but since /sys is populated during bootup,
anything you change by hand will not survive a reboot.  I would think
you would have to find out what creates the file and then get it to
create it with the permissions you want.  I'm not sure but could udev be
doing this? 

I'm not sure about the security concerns but I do see why having a user
being able to adjust the brightness would be a good idea.  I wonder why
it is set up the way it is? 

Dale

:-)  :-)

Re: [gentoo-user] Permissions of files in /sys/

[Alan McKinnon]

On Wednesday 07 January 2009 19:43:54 Dale wrote:

> I have never did this but since /sys is populated during bootup,
> anything you change by hand will not survive a reboot.  I would think
> you would have to find out what creates the file and then get it to
> create it with the permissions you want.  I'm not sure but could udev be
> doing this?


Yes.


-- 
alan dot mckinnon at gmail dot com

Re: [gentoo-user] Permissions of files in /sys/

[Dale]

Alan McKinnon wrote:
> On Wednesday 07 January 2009 19:43:54 Dale wrote:
>
>   
>> I have never did this but since /sys is populated during bootup,
>> anything you change by hand will not survive a reboot.  I would think
>> you would have to find out what creates the file and then get it to
>> create it with the permissions you want.  I'm not sure but could udev be
>> doing this?
>>     
>
>
> Yes.
>
>
>   

So sounds like he should find and edit the udev rule or make his own
rule and set the permissions like he wants.

Also, could he change just this one file in /sys and not have security
concerns?

Whenever the OP comes back, he's got some catching up to do.  LOL

Dale

:-)  :-)

Re: [gentoo-user] Permissions of files in /sys/

[Paul Hartman]

On Wed, Jan 7, 2009 at 8:29 AM, Momesso Andrea <momesso.andrea@gmail.com> wrote:
> I'd like to make the file /sys/class/backlight/asus-laptop/brightness
> writeable for users, so that I don't need to be root anymore to change
> the brightness.
>
> Of course I can chown or chmod ot in local.start but I'm asking if there
> is a cleaner way.

I guess you need to use udevinfo to get the important information
about /sys/class/backlight/asus-laptop/brightness and then write up a
rule, slap it into a file in /etc/udev/rules.d/ and enjoy your new
permissions. :) I don't have that device on my system so I can't
really suggest anything more specific.

Here's a udev rules HOWTO that might help:

http://www.reactivated.net/writing_udev_rules.html

(specifically "Controlling permissions and ownership")

Good luck :)
Paul

Re: [gentoo-user] Permissions of files in /sys/

[Andrea Momesso]

On Wed, Jan 7, 2009 at 9:47 PM, Paul Hartman
<paul.hartman+gentoo@gmail.com> wrote:
> On Wed, Jan 7, 2009 at 8:29 AM, Momesso Andrea <momesso.andrea@gmail.com> wrote:
>> I'd like to make the file /sys/class/backlight/asus-laptop/brightness
>> writeable for users, so that I don't need to be root anymore to change
>> the brightness.
>>
>> Of course I can chown or chmod ot in local.start but I'm asking if there
>> is a cleaner way.
>
> I guess you need to use udevinfo to get the important information
> about /sys/class/backlight/asus-laptop/brightness and then write up a
> rule, slap it into a file in /etc/udev/rules.d/ and enjoy your new
> permissions. :) I don't have that device on my system so I can't
> really suggest anything more specific.
>
> Here's a udev rules HOWTO that might help:
>
> http://www.reactivated.net/writing_udev_rules.html
>
> (specifically "Controlling permissions and ownership")
>
> Good luck :)
> Paul
>
>

It looks like I cannot simply write a rule to change that permission...
After experiencing some failures I guess that udev rules can change
permissions on /dev/ files, but not on /sys/ files...

This is my case:

# udevadm info -a -p /sys/class/backlight/asus-laptop/

  looking at device '/class/backlight/asus-laptop':
    KERNEL=="asus-laptop"
    SUBSYSTEM=="backlight"
    DRIVER==""
    ATTR{bl_power}=="0"
    ATTR{brightness}=="5"
    ATTR{actual_brightness}=="5"
    ATTR{max_brightness}=="15"

And this is the rule I added in /etc/udev/rules.d/10-local.rules

KERNEL=="asus-laptop", SUBSYSTEM=="backlight", GROUP="video", MODE="0660"

After a reboot I still get this:

# ls -la /sys/class/backlight/asus-laptop
total 0
drwxr-xr-x 3 root root    0 2009-01-09 15:18 .
drwxr-xr-x 3 root root    0 2009-01-09 15:18 ..
-r--r--r-- 1 root root 4096 2009-01-09 15:18 actual_brightness
-rw-r--r-- 1 root root 4096 2009-01-09 15:19 bl_power
-rw-r--r-- 1 root root 4096 2009-01-09 17:02 brightness
-r--r--r-- 1 root root 4096 2009-01-09 15:18 max_brightness
drwxr-xr-x 2 root root    0 2009-01-09 15:19 power
lrwxrwxrwx 1 root root    0 2009-01-09 15:18 subsystem -> ../../backlight
-rw-r--r-- 1 root root 4096 2009-01-09 15:18 uevent

Googling a bit I found some solutions [1] [2], but all of them are
changing the permissions at every
boot. It works, but it looks to me a bit unclean...
[1] http://wiki.laptop.org/go/Xfce_keybindings#Adjust_screen_brightness_buttons
[2] http://www.thinkwiki.org/wiki/Automatically_reduce_brightness

-- 
Momesso (TopperH) Andrea
http://topperh.blogspot.com
Jabber: topper_harley@jabber.org
ICQ: 224179391

Re: [gentoo-user] Permissions of files in /sys/

[Momesso Andrea]

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On Fri, Jan 09, 2009 at 05:28:40PM +0100, Andrea Momesso wrote:
> On Wed, Jan 7, 2009 at 9:47 PM, Paul Hartman
> <paul.hartman+gentoo@gmail.com> wrote:
> > On Wed, Jan 7, 2009 at 8:29 AM, Momesso Andrea <momesso.andrea@gmail.com> wrote:
> >> I'd like to make the file /sys/class/backlight/asus-laptop/brightness
> >> writeable for users, so that I don't need to be root anymore to change
> >> the brightness.
> >>
> >> Of course I can chown or chmod ot in local.start but I'm asking if there
> >> is a cleaner way.
> >
> > I guess you need to use udevinfo to get the important information
> > about /sys/class/backlight/asus-laptop/brightness and then write up a
> > rule, slap it into a file in /etc/udev/rules.d/ and enjoy your new
> > permissions. :) I don't have that device on my system so I can't
> > really suggest anything more specific.
> >
> > Here's a udev rules HOWTO that might help:
> >
> > http://www.reactivated.net/writing_udev_rules.html
> >
> > (specifically "Controlling permissions and ownership")
> >
> > Good luck :)
> > Paul
> >
> >
> 
> It looks like I cannot simply write a rule to change that permission...
> After experiencing some failures I guess that udev rules can change
> permissions on /dev/ files, but not on /sys/ files...
> 
> This is my case:
> 
> # udevadm info -a -p /sys/class/backlight/asus-laptop/
> 
>   looking at device '/class/backlight/asus-laptop':
>     KERNEL=="asus-laptop"
>     SUBSYSTEM=="backlight"
>     DRIVER==""
>     ATTR{bl_power}=="0"
>     ATTR{brightness}=="5"
>     ATTR{actual_brightness}=="5"
>     ATTR{max_brightness}=="15"
> 
> And this is the rule I added in /etc/udev/rules.d/10-local.rules
> 
> KERNEL=="asus-laptop", SUBSYSTEM=="backlight", GROUP="video", MODE="0660"
> 
> After a reboot I still get this:
> 
> # ls -la /sys/class/backlight/asus-laptop
> total 0
> drwxr-xr-x 3 root root    0 2009-01-09 15:18 .
> drwxr-xr-x 3 root root    0 2009-01-09 15:18 ..
> -r--r--r-- 1 root root 4096 2009-01-09 15:18 actual_brightness
> -rw-r--r-- 1 root root 4096 2009-01-09 15:19 bl_power
> -rw-r--r-- 1 root root 4096 2009-01-09 17:02 brightness
> -r--r--r-- 1 root root 4096 2009-01-09 15:18 max_brightness
> drwxr-xr-x 2 root root    0 2009-01-09 15:19 power
> lrwxrwxrwx 1 root root    0 2009-01-09 15:18 subsystem -> ../../backlight
> -rw-r--r-- 1 root root 4096 2009-01-09 15:18 uevent
> 
> Googling a bit I found some solutions [1] [2], but all of them are
> changing the permissions at every
> boot. It works, but it looks to me a bit unclean...
> [1] http://wiki.laptop.org/go/Xfce_keybindings#Adjust_screen_brightness_buttons
> [2] http://www.thinkwiki.org/wiki/Automatically_reduce_brightness
> 

Hmmm... Having not recived any answers might mean that my suspects are
right and there is no way to create an udev rule for my scope.

I think I will have to change those permissions manually at boot time

Thanks anyway for help

-- 
Momesso (TopperH) Andrea
http://topperh.blogspot.com
Jabber: topper_harley@jabber.org
ICQ: 224179391

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Re: [gentoo-user] Permissions of files in /sys/

[Neil Bothwick]

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On Mon, 12 Jan 2009 19:13:32 +0100, Momesso Andrea wrote:

> Hmmm... Having not recived any answers might mean that my suspects are
> right and there is no way to create an udev rule for my scope.

udev rules create and name files in /dev. They use information from /sys
but don't write there.

> I think I will have to change those permissions manually at boot time

You may be able t achieve this with a HAL policy rule, but a chown/chmod
in /etc/conf.d/local is less hassle to implement.


-- 
Neil Bothwick

It may be that your sole purpose in life is simply to serve as a warning
to others.

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Re: [gentoo-user] Permissions of files in /sys/

[Andrea Momesso]

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Re: [gentoo-user] Permissions of files in /sys/

[Francisco Ares]

?

On Tue, Jan 13, 2009 at 4:19 AM, Andrea Momesso
<momesso.andrea@gmail.com> wrote:
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>

Re: [gentoo-user] Permissions of files in /sys/

[Volker Armin Hemmann]

On Dienstag 13 Januar 2009, Andrea Momesso wrote:
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great, sending a mail to a public ml that nobody can read. ...

Re: [gentoo-user] Permissions of files in /sys/

[Neil Bothwick]

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On Tue, 13 Jan 2009 11:53:17 +0100, Volker Armin Hemmann wrote:

> great, sending a mail to a public ml that nobody can read. ...

That's not quite true, I could read it :P


-- 
Neil Bothwick

Philosophical error: Demonstrate the existence of a key to continue

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Re: [gentoo-user] Permissions of files in /sys/

[Momesso Andrea]

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On Mon, Jan 12, 2009 at 11:54:01PM +0000, Neil Bothwick wrote:
> On Mon, 12 Jan 2009 19:13:32 +0100, Momesso Andrea wrote:
> 
> > Hmmm... Having not recived any answers might mean that my suspects are
> > right and there is no way to create an udev rule for my scope.
> 
> udev rules create and name files in /dev. They use information from /sys
> but don't write there.

This is exactly what I needed to know.

> 
> > I think I will have to change those permissions manually at boot time
> 
> You may be able t achieve this with a HAL policy rule, but a chown/chmod
> in /etc/conf.d/local is less hassle to implement.

Yes, I will go this way.

TopperH

===========================
Momesso Andrea
http://topperh.blogspot.com
===========================

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Re: [gentoo-user] Permissions of files in /sys/

[Momesso Andrea]

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On Tue, Jan 13, 2009 at 06:17:32AM -0200, Francisco Ares wrote:
> ?
> 
> On Tue, Jan 13, 2009 at 4:19 AM, Andrea Momesso
> <momesso.andrea@gmail.com> wrote:
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> >
> >

Sorry about that...

I'm so used to mail with mutt that when it's not available I make
terrible mistakes...

TopperH

===========================
Momesso Andrea
http://topperh.blogspot.com
===========================

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Re: [gentoo-user] Permissions of files in /sys/

[Volker Armin Hemmann]

On Dienstag 13 Januar 2009, Neil Bothwick wrote:
> On Tue, 13 Jan 2009 11:53:17 +0100, Volker Armin Hemmann wrote:
> > great, sending a mail to a public ml that nobody can read. ...
>
> That's not quite true, I could read it :P

as I said... :P

Re: [gentoo-user] Permissions of files in /sys/

[Neil Bothwick]

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On Tue, 13 Jan 2009 12:11:20 +0100, Volker Armin Hemmann wrote:

> > > great, sending a mail to a public ml that nobody can read. ...  

> > That's not quite true, I could read it :P  

> as I said... :P

Miaow!

;-) 


-- 
Neil Bothwick

If Bill Gates had a dime for every time a Windows box crashed...
 ...Oh, wait a minute, he already does.

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Re: [gentoo-user] Permissions of files in /sys/

[pk]

Momesso Andrea wrote:

<snip>

> Hmmm... Having not recived any answers might mean that my suspects are
> right and there is no way to create an udev rule for my scope.
> 
> I think I will have to change those permissions manually at boot time

You can make udev run a *sh script... man udev, locate RUN keyword.

Best regards

Peter K