Hide boot on-screen errors, or get TV-out working on ATI Radeon X300

[Tom H]

Sorry. Sent to devel-discuss@ by mistake!

On Mon, Dec 8, 2014 at 6:04 AM, Tom H <tomh0665 at gmail.com> wrote:
> On Mon, Dec 8, 2014 at 2:45 AM, Marius Gedminas <marius at pov.lt> wrote:
>> On Sun, Dec 07, 2014 at 02:33:47PM -0500, John Hupp wrote:
>>>
>>> I created /etc/sysctl.d/20-quiet-printk.conf with content:
>>> kernel.printk = 3 3 3 3
>>> ...
>>> Though I was curious to know a bit more about the mechanisms in
>>> play, I didn't dig much further than that.  I wondered, for
>>> instance, what behavior the default '4 4 1 7' specified, but never
>>> did find out.  The files in sysctl.d are installed by procps (see
>>> the List of Files link at
>>> http://packages.ubuntu.com/trusty/admin/procps). And these, in turn,
>>> are part of the kernel configuration governed by sysctl (see
>>> http://manpages.ubuntu.com/manpages/trusty/en/man8/sysctl.8.html).
>>>
>>> Still looking for the meaning of '4 4 1 7' vs '3 3 3 3' I came to
>>> https://www.kernel.org/doc/Documentation/printk-formats.txt, but my
>>> eyes glazed over just skimming that, and I stopped there.
>>
>> This is a bit unobvious, but you can find the description of the
>> kernel.printk sysctl setting in
>> http://manpages.ubuntu.com/manpages/trusty/en/man5/proc.5.html:
>>
>>     /proc/sys/kernel/printk
>>         The four values in this file are console_loglevel,  default_mes‐
>>         sage_loglevel,     minimum_console_level,    and    default_con‐
>>         sole_loglevel.  These values influence  printk()  behavior  when
>>         printing or logging error messages.  See syslog(2) for more info
>>         on the different loglevels.  Messages  with  a  higher  priority
>>         than  console_loglevel will be printed to the console.  Messages
>>         without an explicit  priority  will  be  printed  with  priority
>>         default_message_level.   minimum_console_loglevel is the minimum
>>         (highest)  value  to  which   console_loglevel   can   be   set.
>>         default_console_loglevel   is   the   default   value  for  con‐
>>         sole_loglevel.
>>
>> (/proc/sys is one of the possible ways of changing systcl settings,
>> which I guess explain why this is documented in proc(5).)
>
> You can find the same explanation of the four _loglevels in
> https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
> in a more readable format (to my eyes).
>
> As mentioned in "man 5 proc", you'll find the explanation of the
> priorities in "man 2 syslog"; you can also find it in
> "/usr/include/x86_64-linux-gnu/.../syslog.h" (on x86_64/amd64).
>
> "man 2 syslog" on 15.04 also includes the text of the kernel.org
> document above (clarified/updated).
>
> If you're not on 15.04, you can get the latest man-pages (manpages in
> Ubuntu) from
> https://www.kernel.org/pub/linux/docs/man-pages/
> untar it, and run "man man-pages-3.75/man2/syslog.2"
>
> "3 4 1 3" is a more standard setting than "3 3 3 3".
>
> It's better to set 4 (WARNING, the vanilla default) rather than 3
> (ERR) for messages that don't have a priority, since, if a message
> really is an error, it'll (should?) be tagged as such.
>
> By setting minimum_console_loglevel to 3, you're potentially making
> printk more verbose on the console.