Printk output on console

Printk output on console

[srinivas naga vutukuri]

Hi Selva,
 
 I understood the question as where all/what all printks (with
 line nos and the file names)
 you are looking for is it. I think, in a normal printf  using the
 macros __FILE__ and __LINE__ will give that...
 
 ex:
 printk(KERN_ERR "%s: Driver Initialisation failed", __FILE__);
 Is this helpful...
 
Regards,
srinivas.

Re: Printk output on console

[selvakumar nagendran]

Hi srinivas,
     My question is "We are having lot more printk
statements in the kernel source files. While the
kernel is in execution where the output of all these
statements will go? and can we redirect the output of
printk to our console?
     Please help me. Also I have one more error after
having compiled my new kernel 2.6.9. After booting it
shows the following error

"Kernel panic syncing unable to mount block(0,0) VFS
specify root =LABEL correctly"
  Do u know how to deal with it?

Thanks,
selva
--- srinivas naga vutukuri
<srinivas.vutukuri@gmail.com> wrote:

> Hi Selva,
>  
>  I understood the question as where all/what all
> printks (with
>  line nos and the file names)
>  you are looking for is it. I think, in a normal
> printf  using the
>  macros __FILE__ and __LINE__ will give that...
>  
>  ex:
>  printk(KERN_ERR "%s: Driver Initialisation failed",
> __FILE__);
>  Is this helpful...
>  
> Regards,
> srinivas.
> -
> To unsubscribe from this list: send the line
> "unsubscribe linux-kernel" in
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> 



		
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Re: Printk output on console

[srinivas naga vutukuri]

Hi Selva,

You can go through, one of the help link on the log msgs...
     http://www.hk8.org/old_web/linux/run/ch08_03.htm
I think, they(kernel printk's) are directing to the console only...
Or you can observe, initially while booting it up, after console initiation
happened, it starts buffering out all the printk's output to the console
only.

But i did't remember, the code flow, at a particular point, the X or
something
the shell will take over of it...But any emergency msgs, from the kernel,
will be
coming onto the Console only...

I think, for your error msg, you can better google it...Its not able to
recognise,
the boot partition may be...

Regards,
srinivas.



----- Original Message -----
From: "selvakumar nagendran" <kernelselva@yahoo.com>
To: "srinivas naga vutukuri" <srinivas.vutukuri@gmail.com>
Cc: <linux-kernel@vger.kernel.org>
Sent: Tuesday, December 21, 2004 3:13 PM
Subject: Re: Printk output on console


> Hi srinivas,
>      My question is "We are having lot more printk
> statements in the kernel source files. While the
> kernel is in execution where the output of all these
> statements will go? and can we redirect the output of
> printk to our console?
>      Please help me. Also I have one more error after
> having compiled my new kernel 2.6.9. After booting it
> shows the following error
>
> "Kernel panic syncing unable to mount block(0,0) VFS
> specify root =LABEL correctly"
>   Do u know how to deal with it?
>
> Thanks,
> selva
> --- srinivas naga vutukuri
> <srinivas.vutukuri@gmail.com> wrote:
>
> > Hi Selva,
> >
> >  I understood the question as where all/what all
> > printks (with
> >  line nos and the file names)
> >  you are looking for is it. I think, in a normal
> > printf  using the
> >  macros __FILE__ and __LINE__ will give that...
> >
> >  ex:
> >  printk(KERN_ERR "%s: Driver Initialisation failed",
> > __FILE__);
> >  Is this helpful...
> >
> > Regards,
> > srinivas.
> > -
> > To unsubscribe from this list: send the line
> > "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at
> > http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> >
>
>
>
>
> __________________________________
> Do you Yahoo!?
> Read only the mail you want - Yahoo! Mail SpamGuard.
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Re: Printk output on console

[Luca Falavigna]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi Selvakumar,
| While the
|> kernel is in execution where the output of all these
|> statements will go?

printk messages go to /proc/kmsg. You can read them using cat (e.g. cat
/proc/kmsg)
| can we redirect the output of
|> printk to our console?

There is another way to display kernel messages on a console: managing
ttys. Here is some code (taken from Peter Salzman's "The Linux Kernel
Module Programming Guide"):

static void print_string(char *str)
{
	struct tty_struct *tty;

#if ( LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,5) )
	tty = current->tty;
#else
	tty = current->signal->tty;
#endif

	if (!tty)
		return;

	((my_tty->driver)->write) (my_tty, 0, str, strlen(str));
	((my_tty->driver)->write) (my_tty, 0, "\015\012", 2);

}

Regards,

					Luca
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Printk output on console

[selvakumar nagendran]

 How can we see the output of printk calls in kernel
source files in our console. Is there any special
command or utility for it?
 How to view the output of printk on our console? What
is the log level to be set for this?

Thanks,
selva



		
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Re: Printk output on console

[Robin Jose]

You can refer to Rubini's book "Linux Device Drivers 2nd Edition". See
section "How messages gets logged" in Chapter 4, which explains in
detail how to use printk for debugging.

This book is now available online, under Oreilly's open book project
http://www.xml.com/ldd/chapter/book/ch04.html

Thanks,
Robin

On Mon, 20 Dec 2004 22:32:22 -0800 (PST), selvakumar nagendran
<kernelselva@yahoo.com> wrote:
> How can we see the output of printk calls in kernel
> source files in our console. Is there any special
> command or utility for it?
> How to view the output of printk on our console? What
> is the log level to be set for this?
> 
> Thanks,
> selva
> 
> __________________________________
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