212 lines
4.1 KiB
HTML
212 lines
4.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Troubleshooting</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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TITLE="The Linux 2.4 SCSI subsystem HOWTO"
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TITLE="Changes during the lk 2.4 series"
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TITLE="Performance, Test and Debugging tools"
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><TR
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>The Linux 2.4 SCSI subsystem HOWTO</TH
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><DIV
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CLASS="appendix"
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><H1
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><A
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NAME="trouble"
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></A
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>Appendix C. Troubleshooting</H1
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><P
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> Many SCSI problems are caused by cabling and (lack of, or inappropriate)
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termination. This often results in repeated SCSI bus resets, parity
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or CRC errors and sometimes reduced transfer speeds. There is a good
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SCSI termination tutorial at this site:
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<A
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HREF="http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html"
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TARGET="_top"
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> www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html</A
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>. There is
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other useful SCSI information at that site (see <A
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HREF="refs.html#W9"
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>W9</A
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>).
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</P
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><P
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> There is also a SCSI "faq" site (see <A
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HREF="refs.html#W10"
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>W10</A
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>)
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that addresses many configuration and troubleshooting issues. Although
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the main focus of this site is Windows (and its ASPI interface), much
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is relevant to SCSI in Linux and other Unix implementations.
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</P
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><P
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> When it looks like something has partially locked up the system, the
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<B
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CLASS="command"
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>ps</B
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> command can be useful for finding out what may be
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causing the problem. The following options may be useful for identifying what
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part of the kernel may be causing the problem. This information could be
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forwarded to the maintainers.
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> ps -eo cmd,wchan
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ps -eo fname,tty,pid,stat,pcpu,wchan
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ps -eo pid,stat,pcpu,nwchan,wchan=WIDE-WCHAN-COLUMN -o args
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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The most interesting option for finding the location of the "hang" is
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"wchan". If this is a kernel address then <B
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CLASS="command"
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>ps</B
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> will
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use <TT
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CLASS="filename"
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>/proc/ksyms</TT
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> to find the nearest symbolic
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location. The "nwchan" option outputs the numerical address of the "hang".
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</P
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><P
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> If the system is not responding to keystrokes, then <Alt+ScrollLock>
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in text mode should output a stack trace while <Ctrl+ScrollLock>
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should output a list of all processes. If the log is still working, the
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output will be sent there as well as appearing on the console.
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</P
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><P
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> If the kernel has been built with the CONFIG_MAGIC_SYSRQ, then in text
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mode <Alt+SysRq+H> will list available commands. Of these <Alt+SysRq+S>
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is useful for doing an emergency sync while <Alt+SysRq+U> will remount
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file systems in read only mode. After that <Alt+SysRq+B> to reboot the
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machine might be your next move.
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</P
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>Prev</A
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Changes during the lk 2.4 series</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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> </TD
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>Performance, Test and Debugging tools</TD
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> |