add directory study
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<HTML
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><HEAD
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><TITLE
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>Troubleshooting, or The Agony of Defeat</TITLE
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><META
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CONTENT="Modular DocBook HTML Stylesheet Version 1.63
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"><LINK
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REL="HOME"
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TITLE="The Linux Bootdisk HOWTO"
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HREF="index.html"><LINK
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REL="PREVIOUS"
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TITLE="Putting them together: Making the diskette(s)"
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HREF="x703.html"><LINK
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REL="NEXT"
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TITLE="Reducing root filesystem size"
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><BODY
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CLASS="SECT1"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>The Linux Bootdisk HOWTO</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="x703.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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></TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="slimfast.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="TROUBLESHOOTING"
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>7. Troubleshooting, or The Agony of Defeat</A
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></H1
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><P
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>When building bootdisks, the first few tries often will not boot. The general
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approach to building a root disk is to assemble components from your existing
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system, and try and get the diskette-based system to the point where it displays
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messages on the console. Once it starts talking to you, the battle is half over
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because you can see what it is complaining about, and you can fix individual
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problems until the system works smoothly. If the system just hangs with no
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explanation, finding the cause can be difficult. The recommended procedure for
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investigating the problem where the system will not talk to you is as follows:</P
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><P
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> <P
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></P
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><UL
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><LI
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><P
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>You may see a message like this:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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="SCREEN"
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>Kernel panic: VFS: Unable to mount root fs on XX:YY</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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This is a common problem and it has only a few causes. First, check the device
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<EM
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>XX:YY</EM
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> against the list of device codes in
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<TT
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CLASS="FILENAME"
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>/usr/src/linux/Documentation/devices.txt</TT
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>. If it is
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incorrect, you probably didn't do an <B
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CLASS="COMMAND"
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>rdev -R</B
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>, or you did it
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on the wrong image. If the device code is correct, then check carefully the
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device drivers compiled into your kernel. Make sure it has floppy disk, ramdisk
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and ext2 filesystem support built-in.</P
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></LI
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><LI
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><P
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>If you see many errors like:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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="SCREEN"
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>end_request: I/O error, dev 01:00 (ramdisk), sector NNN</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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This is an I/O error from the ramdisk driver, usually because the kernel is
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trying to write beyond the end of the device. The ramdisk is too small to hold
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the root filesystem. Check your bootdisk kernel's initialization messages for a
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line like:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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="SCREEN"
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> Ramdisk driver initialized : 16 ramdisks of 4096K size</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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Check this size against the <EM
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>uncompressed</EM
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> size of
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the root filesystem. If the ramdisks aren't large enough, make them
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larger.</P
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></LI
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><LI
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><P
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>Check that the root disk actually contains the directories you think
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it does. It is easy to copy at the wrong level so that you end up
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with something like <TT
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CLASS="FILENAME"
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>/rootdisk/bin</TT
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> instead of
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<TT
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CLASS="FILENAME"
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>/bin</TT
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> on your root diskette. </P
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></LI
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><LI
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><P
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>Check that there is a <TT
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CLASS="FILENAME"
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>/lib/libc.so</TT
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> with the same link that
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appears in your <TT
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CLASS="FILENAME"
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>/lib</TT
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> directory on your hard disk. </P
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></LI
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><LI
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><P
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>Check that any symbolic links in your <TT
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CLASS="FILENAME"
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>/dev</TT
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>
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directory in your existing system also exist on your root diskette
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filesystem, where those links are to devices which you have included
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in your root diskette. In particular,
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<TT
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CLASS="FILENAME"
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>/dev/console</TT
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> links are essential in many cases.</P
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></LI
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><LI
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><P
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>Check that you have included <TT
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CLASS="FILENAME"
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>/dev/tty1, /dev/null, /dev/zero,
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/dev/mem, /dev/ram</TT
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> and <TT
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CLASS="FILENAME"
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>/dev/kmem</TT
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> files. </P
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></LI
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><LI
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><P
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>Check your kernel configuration -- support for all resources
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required up to login point must be built in, not modules.
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So <EM
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>ramdisk and ext2 support must be built-in</EM
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>. </P
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></LI
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><LI
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><P
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>Check that your kernel root device and ramdisk settings are correct. </P
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></LI
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></UL
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></P
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><P
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>Once these general aspects have been covered, here are some more
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specific files to check:
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<P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Make sure <B
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CLASS="COMMAND"
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>init</B
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> is included as
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<TT
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CLASS="FILENAME"
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>/sbin/init</TT
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> or <TT
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CLASS="FILENAME"
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>/bin/init</TT
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>.
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Make sure it is executable.</P
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></LI
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><LI
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><P
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>Run <B
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CLASS="COMMAND"
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>ldd init</B
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> to check init's libraries. Usually
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this is just <TT
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CLASS="FILENAME"
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>libc.so</TT
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>, but check anyway. Make
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sure you included the necessary libraries and loaders.</P
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></LI
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><LI
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><P
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>Make sure you have the right loader for your libraries --
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<TT
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CLASS="FILENAME"
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>ld.so</TT
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> for a.out or <TT
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CLASS="FILENAME"
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>ld-linux.so</TT
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>
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for ELF. </P
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></LI
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><LI
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><P
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>Check the <TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> on your bootdisk filesystem for
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the calls to <B
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CLASS="COMMAND"
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>getty</B
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> (or some <B
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CLASS="COMMAND"
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>getty</B
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>-like
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program, such as <B
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CLASS="COMMAND"
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>agetty</B
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>, <B
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CLASS="COMMAND"
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>mgetty</B
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> or
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<B
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CLASS="COMMAND"
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>getty_ps</B
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>). Double-check these against your hard
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disk <TT
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CLASS="FILENAME"
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>inittab</TT
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>. Check the man pages of the program you use
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to make sure these make sense. <TT
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CLASS="FILENAME"
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>inittab</TT
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> is possibly the
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trickiest part because its syntax and content depend on the init program used
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and the nature of the system. The only way to tackle it is to read the man
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pages for <B
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CLASS="COMMAND"
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>init</B
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> and <TT
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CLASS="FILENAME"
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>inittab</TT
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> and work
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out exactly what your existing system is doing when it boots. Check to make
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sure <TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> has a system initialisation entry.
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This should contain a command to execute the system initialization script,
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which must exist. </P
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></LI
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><LI
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><P
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> As with <B
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CLASS="COMMAND"
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>init</B
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>, run <B
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CLASS="COMMAND"
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>ldd</B
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> on your
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<B
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CLASS="COMMAND"
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>getty</B
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> to see what it needs, and make sure the necessary
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library files and loaders were included in your root filesystem. </P
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></LI
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><LI
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><P
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>Be sure you have included a shell program (e.g., <B
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CLASS="COMMAND"
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>bash</B
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> or
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<B
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CLASS="COMMAND"
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>ash</B
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>)
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capable of running all of your rc scripts. </P
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></LI
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><LI
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><P
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>If you have a <TT
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CLASS="FILENAME"
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>/etc/ld.so.cache</TT
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> file on your rescue disk,
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remake it.</P
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></LI
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></OL
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> </P
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><P
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>If <B
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CLASS="COMMAND"
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>init</B
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> starts, but you get a message like:
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<TABLE
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BORDER="1"
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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="SCREEN"
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> Id xxx respawning too fast: disabled for 5 minutes </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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it is coming from <B
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CLASS="COMMAND"
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>init</B
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>, usually indicating that
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<B
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CLASS="COMMAND"
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>getty</B
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> or <B
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CLASS="COMMAND"
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>login</B
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> is dying as soon as it
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starts up. Check the <B
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CLASS="COMMAND"
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>getty</B
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> and <B
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CLASS="COMMAND"
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>login</B
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>
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executables and the libraries they depend upon. Make sure the invocations in
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> are correct. If you get strange messages
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from <B
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CLASS="COMMAND"
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>getty</B
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>, it may mean the calling form in
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> is wrong.</P
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><P
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> If you get a login prompt, and you enter a valid login name but the
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system prompts you for another login name immediately, the problem may be
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with PAM or NSS. See <A
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HREF="buildroot.html#PAMANDNSS"
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>Section 4.4</A
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>. The problem may also be
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that you use shadow passwords and didn't copy
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<TT
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CLASS="FILENAME"
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>/etc/shadow</TT
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> to your bootdisk.</P
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><P
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> If you try to run some executable, such as <B
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CLASS="COMMAND"
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>df</B
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>, which
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is on your rescue disk but you yields a message like: <TT
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CLASS="LITERAL"
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>df: not
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found</TT
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>, check two things: (1) Make sure the directory containing the
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binary is in your PATH, and (2) make sure you have libraries (and loaders) the
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program needs. </P
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></DIV
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||||
><DIV
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||||
CLASS="NAVFOOTER"
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||||
><HR
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||||
ALIGN="LEFT"
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||||
WIDTH="100%"><TABLE
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||||
WIDTH="100%"
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||||
BORDER="0"
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||||
CELLPADDING="0"
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||||
CELLSPACING="0"
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><TR
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><TD
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||||
WIDTH="33%"
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||||
ALIGN="left"
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||||
VALIGN="top"
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||||
><A
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||||
HREF="x703.html"
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||||
>Prev</A
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||||
></TD
|
||||
><TD
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||||
WIDTH="34%"
|
||||
ALIGN="center"
|
||||
VALIGN="top"
|
||||
><A
|
||||
HREF="index.html"
|
||||
>Home</A
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||||
></TD
|
||||
><TD
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||||
WIDTH="33%"
|
||||
ALIGN="right"
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||||
VALIGN="top"
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||||
><A
|
||||
HREF="slimfast.html"
|
||||
>Next</A
|
||||
></TD
|
||||
></TR
|
||||
><TR
|
||||
><TD
|
||||
WIDTH="33%"
|
||||
ALIGN="left"
|
||||
VALIGN="top"
|
||||
>Putting them together: Making the diskette(s)</TD
|
||||
><TD
|
||||
WIDTH="34%"
|
||||
ALIGN="center"
|
||||
VALIGN="top"
|
||||
> </TD
|
||||
><TD
|
||||
WIDTH="33%"
|
||||
ALIGN="right"
|
||||
VALIGN="top"
|
||||
>Reducing root filesystem size</TD
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||||
></TR
|
||||
></TABLE
|
||||
></DIV
|
||||
></BODY
|
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></HTML
|
||||
>
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||||
Reference in New Issue
Block a user