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Old 03-18-2015, 08:24 AM   #1
dbuehler
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How to interpret dmesg, kernel.log, etc. ?


Hope this is the proper place to post.

Could someone please direct me to information which details linux boot message format? Specifically, I am troubleshooting a conflict and need to know exactly what the error messages are telling me.

For example, here is are a couple of lines from dmesg for mint17.

Code:
[    0.355993] pci 0000:00:1f.0: address space collision: [io  0x0800-0x087f] conflicts with ACPI CPU throttle [??? 0x00000810-0x00000815 flags 0x80000000]
[    0.355997] pci 0000:00:1f.0: quirk: [io  0x0500-0x053f] claimed by ICH6 GPIO
I can guess that the first field is time from start of boot but what is "pci" in the second field? Is that the name of a module or subroutine in the kernel that is configuring the PCI bus? Likewise for the following fields.

For background information: All works OK on mint13 but I get the error on mint17 and ubuntu. I tried booting some older versions and found the conflict occurs some where bethwen kernel 3.2.0-23 and 3.13.0-37.

Thanks in advance.
 
Old 03-18-2015, 09:16 AM   #2
pan64
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based on this: https://bugs.launchpad.net/ubuntu/+s...y/+bug/1353916 it can be an outdated bios.
 
Old 03-18-2015, 10:50 AM   #3
dbuehler
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Thanks pan64. I was trying to not be too wordy in my original post but perhaps I should have mentioned that I have posted on ubuntu forums for help. So far the problem still exists but my mint13 is supported for a couple more years so all is OK for now.
http://ubuntuforums.org/showthread.php?t=2266046

My question is more about how to read and understand what the kernel is telling me via the logfiles. I know that it must be documented somewhere but I have been unsuccessful in finding it.
 
Old 03-18-2015, 11:27 AM   #4
veerain
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Quote:
Originally Posted by dbuehler View Post
My question is more about how to read and understand what the kernel is telling me via the logfiles. I know that it must be documented somewhere but I have been unsuccessful in finding it.
No. it perhaps is not documentated in one place. You should have little knowledges of hardware, OS terminology, specific drivers and their hardwares. The more you try to read the dmesg day by day the more you get to understand it. And use web search for not understandable words. Some might be hit and some won't be in web search.

And they say Linux is open source and you absolutely must know how to read sources and interpret the produced binaries functioning. (Just kidding).
 
Old 03-18-2015, 05:23 PM   #5
dbuehler
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Hi veerain,

I guess I was hoping for some kind of "secret decoder ring," I have been doing a lot of googling and occasionally I make some progress. Unfortunately, it just seems like a fairly steep learning curve for an older guy like me.
 
Old 03-19-2015, 12:49 AM   #6
veerain
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Try to understand messages which is centered around your domain/know. There are many messages which you wouldn't care at all. Over time you begin to understand the whole flow. Also dmesg is used to know how/what different kernel drivers do while loading/running. If you try to build a kernel you will see there are more than thousand drivers. Each may produce some dmesg message if it loads/runs.
 
Old 03-19-2015, 03:11 AM   #7
pan64
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based on my practice sometimes those messages can only be used as a search string and you need to find detailed description, discussion and explanation somewhere else. There is no way to collect all those messages in a single book....
 
Old 03-19-2015, 03:22 AM   #8
JZL240I-U
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Maybe this is of some help:

http://kernelnewbies.org/
http://sourceforge.net/projects/bootinfoscript/
http://www.dedoimedo.com/computers/bootchart.html
http://0pointer.de/blog/projects/sys...-admins-1.html
http://users.cecs.anu.edu.au/~okeefe...ower2bash.html

Many of those don't directly relate to the messages but to the boot process or e.g. "systemd". That is what you need to understand since it causes the messages. HTH.
 
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Old 03-19-2015, 08:53 AM   #9
dbuehler
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Thanks again for the responses.

Most of the sites listed are new to me so guess I have some homework to do. -

The site about systemd looks particularly interesting so I have downloaded kubuntu 15.04 to play around with it.

To summarize what I think I know now: Files like dmesg are just a running list of kernel messages which are collected by the logging daemon. The actual formatting and content of those messages is controlled buy the individual kernel drivers (if that is the correct term). So, to figure out a specific message in detail I would need to examine the source code for the driver that generated the message. I am not quite there yet but, eventually, I will probably dig into that source code.
 
Old 03-19-2015, 09:43 AM   #10
JZL240I-U
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Since you are interested in "systemd" and if you read German:

http://www.heise.de/open/artikel/Das...1-1563259.html
http://www.heise.de/open/artikel/Das...2-1563461.html

and also for practical purposes "man journalctl" (dmesg equivalent for systemd).

English:
http://www.dedoimedo.com/computers/systemd-blame.html
http://www.dedoimedo.com/computers/k...x-systemd.html

Also, some googleing for Lennart Poettering or Kay Sievers in combination with systemd might be in order (they are the main authors of systemd and at least Lennart Poettering is actively blogging <edit> at http://0pointer.de/blog/ </edit>).

Last edited by JZL240I-U; 03-19-2015 at 10:39 AM.
 
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Old 03-20-2015, 07:19 AM   #11
dbuehler
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Thanks again.

I haven't finished my last homework assignment.

It may take me a while to absorb everything.
 
  


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