Q. I boot from my boot/root disks and nothing happens. What do I do?
See section Troubleshooting , above.
Q. How does the Slackware/Debian/RedHat bootdisk work?
See section Troubleshooting What the pros do , above.
Q. How can I make a boot disk with a XYZ driver?
The easiest way is to obtain a Slackware kernel from your nearest Slackware mirror site. Slackware kernels are generic kernels which atttempt to include drivers for as many devices as possible, so if you have a SCSI or IDE controller, chances are that a driver for it is included in the Slackware kernel.
Go to the a1 directory and select either IDE or SCSI kernel depending on
the type of controller you have. Check the xxxxkern.cfg file for the selected
kernel to see the drivers which have been included in that kernel. If the
device you want is in that list, then the corresponding kernel should boot
your computer. Download the xxxxkern.tgz file and copy it to your boot
diskette as described above in the section on making boot disks.
device drivers/
You must then check the root device in the kernel, using the rdev command:
rdev zImage
rdev will then display the current root device in the kernel. If this
is not the same as the root device you want, then use rdev to change
it. For example, the kernel I tried was set to /dev/sda2, but
my root SCSI partition is /dev/sda8. To use a root diskette,
you would have to use the command:
rdev zImage /dev/fd0
If you want to know how to set up a Slackware root disk as well, that's outside the scope of this HOWTO, so I suggest you check the Linux Install Guide or get the Slackware distribution. See the section in this HOWTO titled ``References''.
Q. How do I update my boot diskette with a new kernel?
kernel, updating/
Just copy the kernel to your boot diskette using the dd command for a boot diskette without a filesystem, or the cp command for a boot/root disk. Refer to the section in this HOWTO titled ``Boot'' for details on creating a boot disk. The description applies equally to updating a kernel on a boot disk.
Q. How do I update my root diskette with new files?
root filesystems, updating/
The easiest way is to copy the filesystem from the rootdisk back to the DEVICE you used (from section Troubleshooting What the pros do Creating the filesystem , above). Then mount the filesystem and make the changes. You have to remember where your root filesystem started and how many blocks it occupied:
dd if=/dev/fd0 bs=1k skip=ROOTBEGIN count=BLOCKS | gunzip > DEVICE
mount -t ext2 DEVICE /mnt
After making the changes, proceed as before (in Section Troubleshooting What the pros do Creating the filesystem Wrapping it up ) and transfer the root filesystem back to the disk. You should not have to re-transfer the kernel or re-compute the ramdisk word if you do not change the starting position of the new root filesystem.
Q. How do I remove LILO so that I can use DOS to boot again?
LILO/ Master Boot Record (MBR)/
This is not really a Bootdisk topic, but it is asked often. Within Linux, you can run:
/sbin/lilo -u
You can also use the dd command to copy the backup saved by LILO to the
boot sector. Refer to the LILO documentation if you wish to do this.
Within DOS and Windows you can use the DOS command:
FDISK /MBR
MBR stands for Master Boot Record, and it replaces the boot sector with a clean DOS one, without affecting the partition table. Some purists disagree with this, but even the author of LILO, Werner Almesberger, suggests it. It is easy, and it works.
Q. How can I boot if I've lost my kernel and my boot disk?
If you don't have a boot disk standing by, probably the easiest method is to obtain a Slackware kernel for your disk controller type (IDE or SCSI) as described above for ``How do I make a boot disk with a XXX driver?''. You can then boot your computer using this kernel, then repair whatever damage there is.
The kernel you get may not have the root device set to the disk type and partition you want. For example, Slackware's generic SCSI kernel has the root device set to /dev/sda2, whereas my root Linux partition happens to be /dev/sda8. In this case the root device in the kernel will have to be changed.
You can still change the root device and ramdisk settings in the kernel even if all you have is a kernel, and some other operating system, such as DOS.
rdev changes kernel settings by changing the values at fixed offsets in
the kernel file, so you can do the same if you have a hex editor available on
whatever systems you do still have running --- for example, Norton
Utilities Disk Editor under DOS. You then need to check and if necessary
change the values in the kernel at the following offsets:
ramdisk word/rdev/
HEX DEC DESCRIPTION
0x01F8 504 Low byte of RAMDISK word
0x01F9 505 High byte of RAMDISK word
0x01FC 508 Root minor device number - see below
0X01FD 509 Root major device number - see below
The interpretation of the ramdisk word was described in Section Troubleshooting What the pros do Creating the filesystem Wrapping it up Setting the ramdisk word , above.
The major and minor device numbers must be set to the device you want to mount your root filesystem on. Some useful values to select from are:
DEVICE MAJOR MINOR
/dev/fd0 2 0 1st floppy drive
/dev/hda1 3 1 partition 1 on 1st IDE drive
/dev/sda1 8 1 partition 1 on 1st SCSI drive
/dev/sda8 8 8 partition 8 on 1st SCSI drive
Once you have set these values then you can write the file to a diskette using
either Norton Utilities Disk Editor, or a program called rawrite.exe.
This program is included in all distributions. It is a DOS program which
writes a file to the ``raw'' disk, starting at the boot sector, instead of
writing it to the file system. If you use Norton Utilities you must write the
file to a physical disk starting at the beginning of the disk.
Q. How can I make extra copies of boot/root diskettes?
Because magnetic media may deteriorate over time, you should keep several copies of your rescue disk, in case the original is unreadable.
The easiest way of making copies of any diskettes, including bootable and
utility diskettes, is to use the dd command to copy the contents of the
original diskette to a file on your hard drive, and then use the same command
to copy the file back to a new diskette. Note that you do not need to, and
should not, mount the diskettes, because dd uses the raw device
interface.
To copy the original, enter the command:
dd if=DEVICENAME of=FILENAME
where DEVICENAME is the device name of the diskette drive
and FILENAME is the name of the (hard-disk) output file
Omitting the count parameter causes dd to copy the whole diskette (2880
blocks if high-density).
To copy the resulting file back to a new diskette, insert the new diskette and enter the reverse command:
dd if=FILENAME of=DEVICENAME
Note that the above discussion assumes that you have only one diskette drive. If you have two of the same type, you can copy diskettes using a command like:
dd if=/dev/fd0 of=/dev/fd1
Q. How can I boot without typing in "ahaxxxx=nn,nn,nn" every time?
kernel, parameters/
Where a disk device cannot be autodetected it is necessary to supply the kernel with a command device parameter string, such as:
aha152x=0x340,11,3,1
lock'' keyword to make it store the
command line as the default command line, so that LILO will use
the same options every time it boots.
append= statement in the LILO config file. Note that
the parameter string must be enclosed in quotes.
For example, a sample command line using the above parameter string would be:
zImage aha152x=0x340,11,3,1 root=/dev/sda1 lock
This would pass the device parameter string through, and also ask the kernel to set the root device to /dev/sda1 and save the whole command line and reuse it for all future boots.
A sample APPEND statement is:
APPEND = "aha152x=0x340,11,3,1"
Note that the parameter string must NOT be enclosed in quotes on the command line, but it MUST be enclosed in quotes in the APPEND statement.
Note also that for the parameter string to be acted on, the kernel must contain the driver for that disk type. If it does not, then there is nothing listening for the parameter string, and you will have to rebuild the kernel to include the required driver. For details on rebuilding the kernel, cd to /usr/src/linux and read the README, and read the Linux FAQ and Installation HOWTO. Alternatively you could obtain a generic kernel for the disk type and install that.
Readers are strongly urged to read the LILO documentation before experimenting
with LILO installation. Incautious use of the BOOT statement can damage
partitions.
Q. At boot time, I get error "A: cannot execute B". Why?
hardcoded locations/
There are several cases of program names being hardcoded in various utilities.
These cases do not occur everywhere, but they may explain why an executable
apparently cannot be found on your system even though you can see that it is
there. You can find out if a given program has the name of another hardcoded
by using the strings command and piping the output through grep.
Known examples of hardcoding are:
reboot must be placed in the /etc directory.
init has caused problems for at least one person, with the
kernel being unable to find init.
To fix these problems, either move the programs to the correct directory,
or change configuration files (e.g. inittab) to point to the correct
directory. If in doubt, put programs in the same directories as they are
on your hard disk, and use the same inittab and /etc/rc.d
files as they appear on your hard disk.
Q. My kernel has ramdisk support, but initializes ramdisks of 0K
Where this occurs, a kernel message like this will appear as the kernel is booting: ramdisk/
Ramdisk driver initialized : 16 ramdisks of 0K size
This is probably because the size has been set to 0 by kernel parameters at boot time. This could possibly be because of an overlooked LILO configuration file parameter:
ramdisk= 0
This was included in sample LILO configuration files in some older distributions, and was put there to override any previous kernel setting. If you have such a line, remove it.
Note that if you attempt to use a ramdisk which has been set to 0K the behaviour can be unpredictable, and can result in kernel panics.
Previous Chapter
Table of contents of this chapter, General table of contents
Top of the document, Beginning of this Chapter