Re: [gentoo-user] CD boot - dmesg buffer depth option?
On Mon, Jul 05, 2010 at 02:17:26PM -0700, Mark Knecht wrote: On Mon, Jul 5, 2010 at 12:11 PM, Willie Wong ww...@math.princeton.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. Thanks for the ideas. I've been trying them but so far no luck. 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 gentoo log_buf_len=18 18 is not a power of two. Why didn't you just try 131072, like I suggested? In maths notation, n = 2^k for some natural number k. 18 fails that miserably. :) Cheers, W -- Willie W. Wong ww...@math.princeton.edu Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire et vice versa ~~~ I. Newton
Re: [gentoo-user] CD boot - dmesg buffer depth option?
On Mon, Jul 05, 2010 at 02:17:26PM -0700, Mark Knecht wrote: On Mon, Jul 5, 2010 at 12:11 PM, Willie Wong ww...@math.princeton.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 ww...@math.princeton.edu Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire et vice versa ~~~ I. Newton
Re: [gentoo-user] CD boot - dmesg buffer depth option?
On Tue, Jul 6, 2010 at 2:45 AM, Willie Wong ww...@math.princeton.edu wrote: On Mon, Jul 05, 2010 at 02:17:26PM -0700, Mark Knecht wrote: On Mon, Jul 5, 2010 at 12:11 PM, Willie Wong ww...@math.princeton.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). Which is exactly why I chose 18 and not 262144. My bad. I switched to 262144 and now I'm getting all the dmesg data back to the very beginning. Thanks! Cheers, Mark
[gentoo-user] CD boot - dmesg buffer depth option?
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? Thanks, Mark
Re: [gentoo-user] CD boot - dmesg buffer depth option?
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. You may also have to pass an additional parameter to dmesg to read the early messages: look at 'man dmesg' and the -s flag. Cheers, W -- Willie W. Wong ww...@math.princeton.edu Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire et vice versa ~~~ I. Newton
Re: [gentoo-user] CD boot - dmesg buffer depth option?
On Mon, Jul 5, 2010 at 12:11 PM, Willie Wong ww...@math.princeton.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. You may also have to pass an additional parameter to dmesg to read the early messages: look at 'man dmesg' and the -s flag. Cheers, W -- Hi Willie, Thanks for the ideas. I've been trying them but so far no luck. 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 gentoo log_buf_len=18 and then boot, but dmesg never goes back to the beginning. I've also tried dmesg -s 30 but still the results are cut off somewhere down in the stack and I never see the first part of the buffer. I'm looking at this page for some info: http://www.kernel.org/pub/linux/kernel/people/gregkh/lkn/lkn_pdf/ch09.pdf Reading about log_buf_len I also see earlyprintk and time options. I tried them at the Live CD command line but it didn't change what I'm getting in dmesg like it did on my regular kernel. I'll continue to study. Thanks, Mark
