Re: [gentoo-user] CD boot - dmesg buffer depth option?

[Willie Wong]

On Mon, Jul 05, 2010 at 02:17:26PM -0700, Mark Knecht wrote:
> On Mon, Jul 5, 2010 at 12:11 PM, Willie Wong <wwong@××××××××××××××.edu> wrote:
> > On Mon, Jul 05, 2010 at 09:16:14AM -0700, Mark Knecht wrote:
> >> I'm trying to capture the full boot log when booting from the Gentoo
> >> install CD but it seems the buffer isn't deep enough to get the whole
> >> thing. Is there by chance a command line option that will increase the
> >> depth of what's captured by dmesg so that I can get all the way back
> >> to the beginning?
> >
> > pass the following parameter to the kernel on GRUB/LILO:
> >
> > log_buf_len=n
> >
> > where n is a power of two. By default it is 16384. You can change it
> > to 131072 (= 2^17) to get a much larger kernel log ring buffer. If you
> > put in something that is not a power of two, the kernel will ignore
> > the option.
> >
>    In my normal booting kernel (on the system hard drive) I did push
> the length up to 18. With that setting dmesg prints all the way back
> to the beginning. However booting the Live CD I hit F1, it shows the
> kernels, so I type
>

to add to the confusion is probably the fact that the in-kernel
configuration parameter is a bit-shift number, and the boot-time
cmdline parameter is actually 2 to that power. So the in-kernel
configuration parameter should be k (=18 in your case), and the
boot-time parameter should be 2^k (=262144).

Cheers, 

W
-- 
Willie W. Wong                                     wwong@××××××××××××××.edu
Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire 
         et vice versa   ~~~  I. Newton