<HTML ><HEAD ><TITLE >Troubleshooting, or The Agony of Defeat</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.63 "><LINK REL="HOME" TITLE="The Linux Bootdisk HOWTO" HREF="index.html"><LINK REL="PREVIOUS" TITLE="Putting them together: Making the diskette(s)" HREF="x703.html"><LINK REL="NEXT" TITLE="Reducing root filesystem size" HREF="slimfast.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >The Linux Bootdisk HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="x703.html" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="slimfast.html" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="TROUBLESHOOTING" >7. Troubleshooting, or The Agony of Defeat</A ></H1 ><P >When building bootdisks, the first few tries often will not boot. The general approach to building a root disk is to assemble components from your existing system, and try and get the diskette-based system to the point where it displays messages on the console. Once it starts talking to you, the battle is half over because you can see what it is complaining about, and you can fix individual problems until the system works smoothly. If the system just hangs with no explanation, finding the cause can be difficult. The recommended procedure for investigating the problem where the system will not talk to you is as follows:</P ><P > <P ></P ><UL ><LI ><P >You may see a message like this: <TABLE BORDER="1" BGCOLOR="#E0E0E0" WIDTH="90%" ><TR ><TD ><FONT COLOR="#000000" ><PRE CLASS="SCREEN" >Kernel panic: VFS: Unable to mount root fs on XX:YY</PRE ></FONT ></TD ></TR ></TABLE > This is a common problem and it has only a few causes. First, check the device <EM >XX:YY</EM > against the list of device codes in <TT CLASS="FILENAME" >/usr/src/linux/Documentation/devices.txt</TT >. If it is incorrect, you probably didn't do an <B CLASS="COMMAND" >rdev -R</B >, or you did it on the wrong image. If the device code is correct, then check carefully the device drivers compiled into your kernel. Make sure it has floppy disk, ramdisk and ext2 filesystem support built-in.</P ></LI ><LI ><P >If you see many errors like: <TABLE BORDER="1" BGCOLOR="#E0E0E0" WIDTH="90%" ><TR ><TD ><FONT COLOR="#000000" ><PRE CLASS="SCREEN" >end_request: I/O error, dev 01:00 (ramdisk), sector NNN</PRE ></FONT ></TD ></TR ></TABLE > This is an I/O error from the ramdisk driver, usually because the kernel is trying to write beyond the end of the device. The ramdisk is too small to hold the root filesystem. Check your bootdisk kernel's initialization messages for a line like: <TABLE BORDER="1" BGCOLOR="#E0E0E0" WIDTH="90%" ><TR ><TD ><FONT COLOR="#000000" ><PRE CLASS="SCREEN" > Ramdisk driver initialized : 16 ramdisks of 4096K size</PRE ></FONT ></TD ></TR ></TABLE > Check this size against the <EM >uncompressed</EM > size of the root filesystem. If the ramdisks aren't large enough, make them larger.</P ></LI ><LI ><P >Check that the root disk actually contains the directories you think it does. It is easy to copy at the wrong level so that you end up with something like <TT CLASS="FILENAME" >/rootdisk/bin</TT > instead of <TT CLASS="FILENAME" >/bin</TT > on your root diskette. </P ></LI ><LI ><P >Check that there is a <TT CLASS="FILENAME" >/lib/libc.so</TT > with the same link that appears in your <TT CLASS="FILENAME" >/lib</TT > directory on your hard disk. </P ></LI ><LI ><P >Check that any symbolic links in your <TT CLASS="FILENAME" >/dev</TT > directory in your existing system also exist on your root diskette filesystem, where those links are to devices which you have included in your root diskette. In particular, <TT CLASS="FILENAME" >/dev/console</TT > links are essential in many cases.</P ></LI ><LI ><P >Check that you have included <TT CLASS="FILENAME" >/dev/tty1, /dev/null, /dev/zero, /dev/mem, /dev/ram</TT > and <TT CLASS="FILENAME" >/dev/kmem</TT > files. </P ></LI ><LI ><P >Check your kernel configuration -- support for all resources required up to login point must be built in, not modules. So <EM >ramdisk and ext2 support must be built-in</EM >. </P ></LI ><LI ><P >Check that your kernel root device and ramdisk settings are correct. </P ></LI ></UL ></P ><P >Once these general aspects have been covered, here are some more specific files to check: <P ></P ><OL TYPE="1" ><LI ><P >Make sure <B CLASS="COMMAND" >init</B > is included as <TT CLASS="FILENAME" >/sbin/init</TT > or <TT CLASS="FILENAME" >/bin/init</TT >. Make sure it is executable.</P ></LI ><LI ><P >Run <B CLASS="COMMAND" >ldd init</B > to check init's libraries. Usually this is just <TT CLASS="FILENAME" >libc.so</TT >, but check anyway. Make sure you included the necessary libraries and loaders.</P ></LI ><LI ><P >Make sure you have the right loader for your libraries -- <TT CLASS="FILENAME" >ld.so</TT > for a.out or <TT CLASS="FILENAME" >ld-linux.so</TT > for ELF. </P ></LI ><LI ><P >Check the <TT CLASS="FILENAME" >/etc/inittab</TT > on your bootdisk filesystem for the calls to <B CLASS="COMMAND" >getty</B > (or some <B CLASS="COMMAND" >getty</B >-like program, such as <B CLASS="COMMAND" >agetty</B >, <B CLASS="COMMAND" >mgetty</B > or <B CLASS="COMMAND" >getty_ps</B >). Double-check these against your hard disk <TT CLASS="FILENAME" >inittab</TT >. Check the man pages of the program you use to make sure these make sense. <TT CLASS="FILENAME" >inittab</TT > is possibly the trickiest part because its syntax and content depend on the init program used and the nature of the system. The only way to tackle it is to read the man pages for <B CLASS="COMMAND" >init</B > and <TT CLASS="FILENAME" >inittab</TT > and work out exactly what your existing system is doing when it boots. Check to make sure <TT CLASS="FILENAME" >/etc/inittab</TT > has a system initialisation entry. This should contain a command to execute the system initialization script, which must exist. </P ></LI ><LI ><P > As with <B CLASS="COMMAND" >init</B >, run <B CLASS="COMMAND" >ldd</B > on your <B CLASS="COMMAND" >getty</B > to see what it needs, and make sure the necessary library files and loaders were included in your root filesystem. </P ></LI ><LI ><P >Be sure you have included a shell program (e.g., <B CLASS="COMMAND" >bash</B > or <B CLASS="COMMAND" >ash</B >) capable of running all of your rc scripts. </P ></LI ><LI ><P >If you have a <TT CLASS="FILENAME" >/etc/ld.so.cache</TT > file on your rescue disk, remake it.</P ></LI ></OL > </P ><P >If <B CLASS="COMMAND" >init</B > starts, but you get a message like: <TABLE BORDER="1" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><FONT COLOR="#000000" ><PRE CLASS="SCREEN" > Id xxx respawning too fast: disabled for 5 minutes </PRE ></FONT ></TD ></TR ></TABLE > it is coming from <B CLASS="COMMAND" >init</B >, usually indicating that <B CLASS="COMMAND" >getty</B > or <B CLASS="COMMAND" >login</B > is dying as soon as it starts up. Check the <B CLASS="COMMAND" >getty</B > and <B CLASS="COMMAND" >login</B > executables and the libraries they depend upon. Make sure the invocations in <TT CLASS="FILENAME" >/etc/inittab</TT > are correct. If you get strange messages from <B CLASS="COMMAND" >getty</B >, it may mean the calling form in <TT CLASS="FILENAME" >/etc/inittab</TT > is wrong.</P ><P > If you get a login prompt, and you enter a valid login name but the system prompts you for another login name immediately, the problem may be with PAM or NSS. See <A HREF="buildroot.html#PAMANDNSS" >Section 4.4</A >. The problem may also be that you use shadow passwords and didn't copy <TT CLASS="FILENAME" >/etc/shadow</TT > to your bootdisk.</P ><P > If you try to run some executable, such as <B CLASS="COMMAND" >df</B >, which is on your rescue disk but you yields a message like: <TT CLASS="LITERAL" >df: not found</TT >, check two things: (1) Make sure the directory containing the binary is in your PATH, and (2) make sure you have libraries (and loaders) the program needs. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="x703.html" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><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 ></TR ></TABLE ></DIV ></BODY ></HTML >
