[clue-tech] help with: "fifo: Permission denied" when using acpi_fakekey as non-root

[chris fedde]

I opened and read /etc/acpi/volupbtn.sh on my ubuntu box.  I see it
uses acpi_fakekey as you say.
I then checked if acpi_fakekey has a man page to see if any clues were
buried  there.
in that man page I found that it used fifos (aka named pipes) in /dev/input/

And that the event numbers are defined in /usr/share/acpi-support/key-constants
I find that

grep KEY_VOLUMEUP /usr/share/acpi-support/key-constants
KEY_VOLUMEUP=115

So the fifo in question is /dev/input/event115 in my case.

But this all begs the real question which is why are these fifos not
writable by the acpid daemon.
I suspect some boot time failure or misconfiguration when acpid is
started at boot time.
so I then started looking in /etc/init.d/acpid for more clues when my
gumption ran out.

Maybe some of this research will be helpful to you.

On Thu, Feb 11, 2010 at 9:49 AM, Jim Ockers <ockers at ockers.net> wrote:
> Hi Mike,
>
> You are going to have to do a bit of detective work.  The brute force way
> might be to just do "find / -type p" as root and see what comes up.
>
> [root]# find / -type p -exec ls -l {} \;
> prw-------    1 root     root            0 Nov 18 15:20 /dev/initctl
> ...
>
> There will be more, I don't know how long the find command will take, but it
> may take a long time depending on your system.  As for which process is
> using it, try 'lsof -n" to see what filehandles each process has open.
>
> Hope this helps,
> Jim
>
> Mike Jensen wrote:
>
> That is VERY helpful.  I did not know that previously.
>
> But that does beg the question, how can I find out which file acpi_fakekey
> is trying to use and does not have the proper permissions for?
>
> Jim Ockers wrote:
>
> Hi Mike,
>
> FIFOs are usually unix pipe special files. Here is an example:
>
> [root at agadez tmp]# touch this_is_a_normal_file
> [root at agadez tmp]# mknod this_is_a_fifo p
> [root at agadez tmp]# ls -al this*
> prw-r--r-- 1 root root 0 Feb 11 07:16 this_is_a_fifo
> -rw-r--r-- 1 root root 0 Feb 11 07:16 this_is_a_normal_file
>
> As you can see the FIFO has permissions associated with it just like any
> other file. Please check the permissions on your FIFO using ls -al and
> see who has permission to write to it and read from it. Here is an
> example of me changing the permissions on my FIFO file:
>
> [root at agadez tmp]# chmod 666 this_is_a_fifo
> [root at agadez tmp]# ls -al this_is_a_fifo
> prw-rw-rw- 1 root root 0 Feb 11 07:16 this_is_a_fifo
>
> I hope this helps,
> Jim
>
> Mike Jensen wrote:
>
>
> Been lurking around for a while, but never posted before.  Sorry to have
> my first post be a help request.
>
> I am trying to get the volume up/down/mute key to work on my Lenovo
> T400.  The distro is Debian Squeeze, fully updated, amd64.  My volume
> keys don't seem to work, so I traced down /etc/acpi/volupbtn.sh (and
> others), and noticed that it was using acpi_fakekey....when I run it as
> such in root, there is no problems, it returns fine.  But when I run the
> same thing as a normal user I get: fifo: Permission denied
>
> Let me know if there is any more information I can provide.  I have
> searched around but have not seen this percise problem before.  Thanks
> in advanced.
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