5. Troubleshooting

When building rescue disks, it is not uncommon that the first few tries 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. To get a system to boot to the stage where it will talk to you requires several components to be present and correctly configured. The recommended procedure for investigating the problem where the system will not talk to you is as follows:

• 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 /root_disk/bin instead of /bin on your root diskette.
• Check that there is a /lib/libc.so and /lib/libtermcap.so, with the same links as appear in your lib directory on your hard disk.
• check that any symbolic links in your /dev 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, /dev/console links are essential in many cases.
• Check that you have included /dev/tty1 on your root disk.
• Check that you have included /dev/null, /dev/zero, /dev/mem, /dev/ram and /dev/kmem devices.
• Check your kernel configuration - support for all resources required up to login point must be built in, not modules. Also, ramdisk support must be included.
• Check that your kernel root device and ramdisk settings are correct. Refer to Section Advanced Bootdisk Creation for details.

Once these general aspects have been covered, here are some more specific files to check:

1. Make sure init is included as /sbin/init or /bin/init. Make sure it's executable.
2. Run ldd init to check init's libraries. Usually this is just libc.so, but check anyway. Make sure you included the libraries.
3. Run file on the library(ies) reported by ldd to see what type they are. Make sure you have the right loader file on the root disk. The loader file is either ld.so (for a.out libraries) or ld-linux.so (for ELF libraries).
4. Check the /etc/inittab on your bootdisk filesystem for the calls to *getty* The notation *getty* will be used to mean some getty-like program, eg getty, agetty, mgetty or getty_ps. . Double-check these against your hard disk inittab. Check the man pages of the program you use to make sure these make sense. Inittab 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 init and inittab and work out exactly what your existing system is doing when it boots. Check to make sure /etc/inittab has a system initialisation entry. This should contain a command of the form /etc/rc.x, to execute one of the /etc/rc scripts. The specific script in the inittab must exist.
5. As with init, run ldd on getty (or agetty) to see what it needs, and make sure the necessary library files and loaders were included in your root filesystem.
6. If you have a /etc/ld.so.cache file on your rescue disk, remake it.

If init starts, but you get a message like:

Id xxx respawning too fast: disabled for n minutes  

it's coming from init, usually indicating that your *getty* or login is dying as soon as it starts up. Check the *getty* and login executables, and the libraries they depend upon. Make sure the invocations in /etc/inittab are correct. If you get strange messages from *getty*, it may mean the calling form in /etc/inittab is wrong. The options of the *getty* programs are variable; even different versions of agetty are reported to have different incompatible calling forms. If you're using a different call and/or program from what you use in your hard disk /etc/inittab, double check it.

If you try to run some executable, such as df, which is on your rescue disk but you yields a message like: df: not found, check two things:

1. Make sure the directory containing the binary is in your PATH.
2. Make sure you have libraries (and loaders) the program needs. Type ldd file to see what libraries are needed, and make sure those libraries exist. See the section above on /lib