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fox2mike 05/07/13 18:58:31 |
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Modified: xml/htdocs/doc/en/draft debugging-howto.xml |
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Log: |
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dmesh patch from Chris White aka PUNK ;) |
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|
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Revision Changes Path |
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1.2 +120 -5 xml/htdocs/doc/en/draft/debugging-howto.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/draft/debugging-howto.xml?rev=1.2&content-type=text/x-cvsweb-markup&cvsroot=gentoo |
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plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/draft/debugging-howto.xml?rev=1.2&content-type=text/plain&cvsroot=gentoo |
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diff : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/draft/debugging-howto.xml.diff?r1=1.1&r2=1.2&cvsroot=gentoo |
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Index: debugging-howto.xml |
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=================================================================== |
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RCS file: /var/cvsroot/gentoo/xml/htdocs/doc/en/draft/debugging-howto.xml,v |
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retrieving revision 1.1 |
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retrieving revision 1.2 |
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diff -u -r1.1 -r1.2 |
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--- debugging-howto.xml 13 Jul 2005 05:55:39 -0000 1.1 |
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+++ debugging-howto.xml 13 Jul 2005 18:58:31 -0000 1.2 |
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@@ -1,6 +1,6 @@ |
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<?xml version="1.0" encoding="UTF-8"?> |
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> |
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-<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/draft/debugging-howto.xml,v 1.1 2005/07/13 05:55:39 fox2mike Exp $ --> |
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+<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/draft/debugging-howto.xml,v 1.2 2005/07/13 18:58:31 fox2mike Exp $ --> |
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|
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<guide link="/doc/en/debugging-howto.xml"> |
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<title>Gentoo Linux Debugging Guide</title> |
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@@ -406,10 +406,125 @@ |
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<body> |
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|
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<p> |
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-Now we've taken care of finding run time bugs. These bugs prove to be |
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-problematic when you try and run your programs. However, run time errors are |
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-the least of your concerns if your program won't compile at all. Let's take a |
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-look at how to address <c>emerge</c> compile errors. |
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+<c>strace</c> is a great way at seeing what the kernel is doing to with the filesystem. |
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+Another program exists to help users see what the kernel is doing, and help with |
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+kernel debugging. This program is called <c>dmesg</c> |
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+</p> |
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+ |
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+</body> |
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+</section> |
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+</chapter> |
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+ |
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+<chapter> |
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+<title>Kernel Debugging With dmesg</title> |
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+<section> |
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+<title>dmesg Introduction</title> |
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+<body> |
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+ |
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+<p> |
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+<c>dmesg</c> is a system program created with debugging kernel operation. It |
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+basically reads the kernel messages and keeps them in buffer, letting the user |
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+see them later on. Here's an example of what a dmesg output looks like: |
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+</p> |
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+ |
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+<pre caption="dmesg sample output"> |
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+SIS5513: IDE controller at PCI slot 0000:00:02.5 |
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+SIS5513: chipset revision 208 |
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+SIS5513: not 100% native mode: will probe irqs later |
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+SIS5513: SiS 961 MuTIOL IDE UDMA100 controller |
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+ide0: BM-DMA at 0x4000-0x4007, BIOS settings: hda:DMA, hdb:DMA |
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+ide1: BM-DMA at 0x4008-0x400f, BIOS settings: hdc:DMA, hdd:DMA |
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+Probing IDE interface ide0... |
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+input: ImPS/2 Generic Wheel Mouse on isa0060/serio1 |
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+hda: WDC WD800BB-60CJA0, ATA DISK drive |
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+hdb: CD-RW 52X24, ATAPI CD/DVD-ROM drive |
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+ide0 at 0x1f0-0x1f7,0x3f6 on irq 14 |
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+Probing IDE interface ide1... |
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+hdc: SAMSUNG DVD-ROM SD-616T, ATAPI CD/DVD-ROM drive |
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+hdd: Maxtor 92049U6, ATA DISK drive |
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+ide1 at 0x170-0x177,0x376 on irq 15 |
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+hda: max request size: 128KiB |
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+hda: 156301488 sectors (80026 MB) w/2048KiB Cache, CHS=65535/16/63, |
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+UDMA(100) |
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+hda: cache flushes not supported |
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+hda: hda1 |
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+hdd: max request size: 128KiB |
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+hdd: 39882528 sectors (20419 MB) w/2048KiB Cache, CHS=39566/16/63, |
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+UDMA(66) |
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+hdd: cache flushes not supported |
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+hdd: unknown partition table |
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+hdb: ATAPI 52X CD-ROM CD-R/RW drive, 2048kB Cache, UDMA(33) |
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+Uniform CD-ROM driver Revision: 3.20 |
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+hdc: ATAPI 48X DVD-ROM drive, 512kB Cache, UDMA(33) |
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+ide-floppy driver 0.99.newide |
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+libata version 1.11 loaded. |
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+usbmon: debugs is not available |
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+</pre> |
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+ |
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+<p> |
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+The dmesg displayed here is my machine's bootup. You can see harddrives and |
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+input devices being initialized. While what you see here seems relatively |
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+harmless, <c>dmesg</c> is also good at showing when things go wrong. Let's take |
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+for example an IPAQ 1945 I have. After a couple of minutes of inactivity, the |
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+device powers off. Now, I have the device connected into the USB port in the |
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+front of my system. Now, I want to copy over some files using libsynCE, so I go |
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+ahead and initiate a connection: |
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+</p> |
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+ |
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+<pre caption="IPAQ connection attempt"> |
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+# <i>synce-serial-start</i> |
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+/usr/sbin/pppd: In file /etc/ppp/peers/synce-device: unrecognized option |
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+'/dev/tts/USB0' |
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+ |
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+synce-serial-start was unable to start the PPP daemon! |
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+</pre> |
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+ |
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+<p> |
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+The connection fails, as we see here, and we assume that only the screen is in |
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+powersave mode, and that maybe the connection is faulty. In order to see what |
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+truly happened, we can use <c>dmesg</c>. Now, <c>dmesg</c> tends to give a |
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+rather large ammount of output. One can use the <c>tail</c> command to help |
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+keep the output down: |
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+</p> |
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+ |
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+<pre caption="Adjusting the output ammount with tail"> |
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+$ <i>dmesg | tail -n 4</i> |
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+usb 1-1.2: PocketPC PDA converter now attached to ttyUSB0 |
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+usb 1-1.2: USB disconnect, address 11 |
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+PocketPC PDA ttyUSB0: PocketPC PDA converter now disconnected from ttyUSB0 |
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+ipaq 1-1.2:1.0: device disconnected |
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+</pre> |
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+ |
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+<p> |
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+This gives us the last 4 lines of the dmesg output. Now, this is enough to give |
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+us some information on the situation. It seems that in the first 2 lines, the |
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+pocketpc is recognized as connected. However, in the last 2 lines, it appears |
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+to have been disconnected. With this information we check the pocketpc again, |
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+and find out it is powered off, and now know about the powersave mode. We can |
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+use this information to turn the feature off, or be aware of it next time. |
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+While this is a somewhat simple example, it does go to show how well dmesg can |
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+work. However, in more complex examples (such as kernel bugs), the entire dmesg |
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+output may be required. To obtain that, simple redirect to a log file as such: |
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+</p> |
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+ |
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+<pre caption="Saving dmesg output to a log"> |
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+$ <i>dmesg > dmesg.log</i> |
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+</pre> |
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+ |
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+<p> |
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+You can then attach this to a bug report, or post it online somewhere for |
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+collaborative debugging sessions. |
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+</p> |
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+ |
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+</body> |
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+</section> |
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+<section> |
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+<title>Conclusion</title> |
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+<body> |
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+ |
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+<p> |
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+Now that we've taken a look at a few ways to debug runtime and kernel errors, |
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+let's take a look at how to handle emerge errors. |
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</p> |
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|
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</body> |
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-- |
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