IT.SOFT 22/ITSOFTCD_22.iso/mac/linux22/slackware3.6/DOCS/BOOTDISK-HOWTO.;1

Text File | 1998-07-05 | 84.3 KB | 2,509 lines | [TEXT/hscd]

  The Linux Bootdisk HOWTO
  Tom Fawcett ([e-mail])


  v3.2, June 1998

  This document describes how to design and build your own boot/root
  diskettes for Linux.  These disks could be used as rescue disks or to
  test new system components.  If you haven't read the Linux FAQ and
  related documents, such as the Linux Installation HOWTO and the Linux
  Install Guide, you should not be trying to build boot diskettes.  If
  you just want a rescue disk to have for emergencies, see Appendix
  ``Pre-made bootdisks''.
  ______________________________________________________________________

  Table of Contents


















































  1. Preface.

     1.1 Version notes.
     1.2 Feedback and credits.
     1.3 Distribution policy.

  2. Introduction.

  3. Bootdisks and the boot process.

     3.1 The boot process.
     3.2 Disk types.

  4. Building a root filesystem.

     4.1 Overview.
     4.2 Creating the filesystem.
     4.3 Populating the filesystem.
        4.3.1 /dev
        4.3.2 /etc
        4.3.3 /bin and /sbin
        4.3.4 /lib
     4.4 Modules.
     4.5 Some final details.
     4.6 Wrapping it up.

  5. Choosing a kernel.

  6. Putting them together: Making the disk(s).

     6.1 Transferring the kernel with LILO
     6.2 Transferring the kernel without LILO.
     6.3 Setting the ramdisk word.
     6.4 Transferring the root filesystem.

  7. Troubleshooting, or The Agony of Defeat.

  8. Miscellaneous topics.

     8.1 Reducing root filesystem size.
     8.2 Non-ramdisk root filesystems.
     8.3 Building a utility disk.

  9. How the pros do it.

  10. Frequently asked question (FAQ) list.

  11. Resources and pointers

     11.1 Pre-made bootdisks.
     11.2 Rescue packages.
     11.3 Graham Chapman's shell scripts
     11.4 LILO --- the Linux loader.
     11.5 Linux FAQ and HOWTOs.
     11.6 Ramdisk usage.
     11.7 The Linux boot process.

  12. LILO boot error codes.

  13. Sample rootdisk directory listings.

  14. Sample utility disk directory listing.




  ______________________________________________________________________

  1.  Preface.


  Note: This document may be outdated. If the date on the title page is
  more than six months ago, please check the Linux Documentation Project
  homepage  <http://sunsite.unc.edu/LDP/> to see if a more recent
  version exists.

  Although this document should be legible in its text form, it looks
  much better in Postscript (.ps) or HTML because of the typographical
  notation used.  We encourage you to select one of these forms.  The
  Info version, as of this writing, ends up so damaged as to be
  unusable.


  1.1.  Version notes.


  Graham Chapman ([e-mail]) wrote the original Bootdisk-HOWTO
  and he supported it through version 3.1.  Tom Fawcett
  ([e-mail]) added a lot of material for kernel 2.0, and he is
  the document's maintainer as of version 3.2.  Much of Chapman's
  original content remains.

  This document is intended for Linux kernel 2.0 and later.  If you have
  an older kernel (1.2.xx or before), please consult previous versions
  of the Bootdisk-HOWTO archived on Graham Chapman's homepage
  <http://www.zeta.org.au/~grahamc/linux.html>.

  This information is intended for Linux on the Intel platform.  Much of
  this information may be applicable to Linux on other processors, but
  we have no first-hand experience or information about this.  If anyone
  has experience with bootdisks on other platforms, please contact us.



  1.2.  Feedback and credits.


  We welcome any feedback, good or bad, on the content of this document.
  We have done our best to ensure that the instructions and information
  herein are accurate and reliable.  Please let us know if you find
  errors or omissions.

  We thank the many people who assisted with corrections and
  suggestions.  Their contributions have made it far better than we
  could ever have done alone.

  Send comments, corrections and questions to the author at the email
  address above.  I don't mind trying to answer questions, but please
  read section ``Troubleshooting'' first.



  1.3.  Distribution policy.


  Copyright © 1995,1996,1997,1998 by Tom Fawcett and Graham Chapman.
  This document may be distributed under the terms set forth in the
  Linux Documentation Project License at
  <http://sunsite.unc.edu/LDP/COPYRIGHT.html>.  Please contact the
  authors if you are unable to get the license.


  This is free documentation.  It is distributed in the hope that it
  will be useful, but without any warranty; without even the implied
  warranty of merchantability or fitness for a particular purpose.




  2.  Introduction.


  Linux boot disks are useful in a number of situations, such as:

  ∑  Testing a new kernel.

  ∑  Recovering from a disk failure --- anything from a lost boot sector
     to a disk head crash.

  ∑  Fixing a disabled system.  A minor mistake as root can leave your
     system unusable, and you may have to boot from diskette to fix it.

  ∑  Upgrading critical system files, such as libc.so.

  There are several ways of obtaining boot disks:


  ∑  Use one from a distribution such as Slackware.  This will at least
     allow you to boot.

  ∑  Use a rescue package to set up disks designed to be used as rescue
     disks.

  ∑  Learn what is required for each of the types of disk to operate,
     then build your own.

  Some people choose the last option so they can do it themselves.  That
  way, if something breaks, they can work out what to do to fix it.
  Plus it's a great way to learn about how a Linux system works.

  This document assumes some basic familiarity with Linux system
  administration concepts.  For example, you should know about
  directories, filesystems and floppy diskettes.  You should know how to
  use mount and df.  You should know what /etc/passwd and fstab files
  are for and what they look like.  You should know that most of the
  commands in this HOWTO should be run as root.

  Constructing your own bootdisk from scratch can be complicated.  If
  you haven't read the Linux FAQ and related documents, such as the
  Linux Installation HOWTO and the Linux Install Guide, you should not
  be trying to build boot diskettes.  If you just need a working
  bootdisk for emergencies, it is much easier to download a
  prefabricated one.  See Appendix ``Pre-made bootdisks'', below, for
  where to find these.



  3.  Bootdisks and the boot process.


  A bootdisk is basically a miniature, self-contained Linux system on a
  floppy diskette.  It must perform many of the same functions that a
  complete full-size Linux system performs.  Before trying to build one
  you should understand the basic Linux boot process.  We present the
  basics here, which are sufficient for understanding the rest of this
  document.  Many details and alternative options have been omitted.


  3.1.  The boot process.


  All PC systems start the boot process by executing code in ROM
  (specifically, the BIOS) to load the sector from sector 0, cylinder 0
  of the boot drive.  The boot drive is usually the first floppy drive
  (designated A: in DOS and /dev/fd0 in Linux).  The BIOS then tries to
  execute this sector.  On most bootable disks, sector 0, cylinder 0
  contains either:

  ∑  code from a boot loader such as LILO, which locates the kernel,
     loads it and executes it to start the boot proper.

  ∑  the start of an operating system kernel, such as Linux.

  If a Linux kernel has been raw-copied to a diskette, the first sector
  of the disk will be the first sector of the Linux kernel itself.  This
  first sector will continue the boot process by loading the rest of the
  kernel from the boot device.

  Once the kernel is completely loaded, it goes through some basic
  device initialization.  It then tries to load and mount a root
  filesystem from some device.  A root filesystem is simply a filesystem
  that is mounted as ``/''.  The kernel has to be told where to look for
  the root filesystem; if it cannot find a loadable image there, it
  halts.

  In some boot situations --- often when booting from a diskette --- the
  root filesystem is loaded into a ramdisk, which is RAM accessed by the
  system as if it were a disk.  There are two reasons why the system
  loads to ramdisk.  First, RAM is several orders of magnitude faster
  than a floppy disk, so system operation is fast; and second, the
  kernel can load a compressed filesystem from the floppy and uncompress
  it onto the ramdisk, allowing many more files to be squeezed onto the
  diskette.

  Once the root filesystem is loaded and mounted, you see a message
  like:


          VFS: Mounted root (ext2 filesystem) readonly.



  init program on the root filesystem (in /bin or /sbin) and executes
  it.  init reads its configuration file /etc/inittab, looks for a line
  designated sysinit, and executes the named script .  The sysinit
  script is usually something like /etc/rc or /etc/init.d/boot.  This
  script is a set of shell commands that set up basic system services,
  such as:


  ∑  Running fsck on all the disks,

  ∑  Loading necessary kernel modules,

  ∑  Starting swapping,

  ∑  Initializing the network,

  ∑  Mounting disks mentioned in fstab.

  This script often invokes various other scripts to do modular
  initialization.  For example, in the common SysVinit structure, the
  directory /etc/rc.d/ contains a complex structure of subdirectories
  whose files specify how to enable and shut down most system services.
  However, on a bootdisk the sysinit script is often very simple.

  When the sysinit script finishes, control returns to init, which then
  enters the default runlevel, specified in inittab with the initdefault
  keyword.  The runlevel line usually specifies a program like getty,
  which is responsible for handling commununications through the console
  and ttys.  It is the getty program which prints the familiar
  ``login:'' prompt.  The getty program in turn invokes the login
  program to handle login validation and to set up user sessions.


  3.2.  Disk types.


  Having reviewed the basic boot process, we can now define various
  kinds of disks involved.  We classify disks into four types.  The
  discussion here and throughout this document uses the term ``disk'' to
  refer to floppy diskettes unless otherwise specified, though most of
  the discussion could apply equally well to hard disks.



     boot
        A disk containing a kernel which can be booted.  The disk can be
        used to boot the kernel, which then may load a root file system
        on another disk.  The kernel on a bootdisk usually must be told
        where to find its root filesystem.

        Often a bootdisk loads a root filesystem from another diskette,
        but it is possible for a bootdisk to be set up to load a hard
        disk's root filesystem instead.  This is commonly done when
        testing a new kernel.  (in fact, ``make zdisk'' will create such
        a bootdisk automatically from the kernel source code).


     root
        A disk with a filesystem containing files required to run a
        Linux system.  Such a disk does not necessarily contain either a
        kernel or a boot loader.

        A root disk can be used to run the system independently of any
        other disks, once the kernel has been booted.  Usually the root
        disk is automatically copied to a ramdisk.  This makes root disk
        accesses much faster, and frees up the disk drive for a utility
        disk.


     boot/root
        A disk which contains both the kernel and a root filesystem.  In
        other words, it contains everything necessary to boot and run a
        Linux system without a hard disk.  The advantage of this type of
        disk is that is it compact --- everything required is on a
        single disk.  However, the gradually increasing size of
        everything means that it is increasingly difficult to fit
        everything on a single diskette, even with compression.


     utility
        A disk which contains a file system, but is not intended to be
        mounted as a root file system.  It is an additional data disk.
        You would use this type of disk to carry additional utilities
        where you have too much to fit on your root disk.




  In general, when we talk about ``building a bootdisk'' we mean
  creating both the boot (kernel) and root (files) portions.  They may
  be either together (a single boot/root disk) or separate (boot + root
  disks).  The most flexible approach for rescue diskettes is probably
  to use separate boot and root diskettes, and one or more utility
  diskettes to handle the overflow.




  4.  Building a root filesystem.


  Creating the root filesystem involves selecting files necessary for
  the system to run.  In this section we describe how to build a
  compressed root filesystem.  A less common option is to build an
  uncompressed filesystem on a diskette that is directly mounted as
  root; this alternative is described in section ``Non-ramdisk Root
  Filesystem''.


  4.1.  Overview.


  A root filesystem must contain everything needed to support a full
  Linux system.  To be able to do this, the disk must include the
  minimum requirements for a Linux system:


  ∑  The basic file system structure,

  ∑  Minimum set of directories: /dev, /proc, /bin, /etc, /lib, /usr,
     /tmp,

  ∑  Basic set of utilities: sh, ls, cp, mv, etc.,

  ∑  Minimum set of config files: rc, inittab, fstab, etc.,

  ∑  Devices: /dev/hd*, /dev/tty*, /dev/fd0, etc.,

  ∑  Runtime library to provide basic functions used by utilities.

  Of course, any system only becomes useful when you can run something
  on it, and a root diskette usually only becomes useful when you can do
  something like:


  ∑  Check a file system on another drive, for example to check your
     root file system on your hard drive, you need to be able to boot
     Linux from another drive, as you can with a root diskette system.
     Then you can run fsck on your original root drive while it is not
     mounted.

  ∑  Restore all or part of your original root drive from backup using
     archive and compression utilities such as cpio, tar, gzip and
     ftape.


  We will describe how to build a compressed filesystem, so called
  because it is compressed on disk and, when booted, is uncompressed
  onto a ramdisk.  With a compressed filesystem you can fit many files
  (approximately two megabytes) onto a standard 1440K diskette.  Because
  the filesystem is much larger than a diskette, it cannot be built on
  the diskette.  We have to build it elsewhere, compress it, then copy
  it to the diskette.

  4.2.  Creating the filesystem.


  In order to build such a root filesystem, you need a spare device that
  is large enough to hold all the files before compression.  You will
  need a device capable of holding about four megabytes.  There are
  several choices:


  ∑  Use a ramdisk (DEVICE = /dev/ram0).  In this case, memory is used
     to simulate a disk drive.  The ramdisk must be large enough to hold
     a filesystem of the appropriate size.  If you use LILO, check your
     configuration file (/etc/lilo.conf) for a line like:


             RAMDISK_SIZE = nnn


  which determines how much RAM will be allocated.  The default is
  4096K, which should be sufficient.  You should probably not try to use
  such a ramdisk on a machine with less than 8MB of RAM.

  Check to make sure you have a device like /dev/ram0, /dev/ram or
  /dev/ramdisk.  If not, create /dev/ram0 with mknod (major number 1,
  minor 0).

  ∑  If you have an unused hard disk partition that is large enough
     (several megabytes), this is a good solution.  If you have enough
     physical RAM you can turn off swapping and build the filesystem in
     your swap partition.

  ∑  Use a loopback device, which allows a disk file to be treated as a
     device.  Using a loopback device you can create a three megabyte
     file on your hard disk and build the filesystem on it.

     In order to use loopback devices you need specially modified mount
     and unmount programs.  You can find these in the directory:

     ftp://ftp.win.tue.nl:/pub/linux/util/mount/


     If you do not have a loop device (/dev/loop0, /dev/loop1, etc.) on
     your system, you will have to create one with ``mknod /dev/loop0 b
     7 0''.  One you've installed these special mount and umount
     binaries, create a temporary file on a hard disk with enough
     capacity (eg, /tmp/fsfile).  You can use a command like


       dd if=/dev/zero of=/tmp/fsfile bs=1k count=nnn


  to create an nnn-block file.

  Use the file name in place of DEVICE below.  When you issue a mount
  command you must include the option ``-o loop'' to tell mount to use a
  loopback device.

          mount -o loop -t ext2 /tmp/fsfile /mnt



  will mount /tmp/fsfile (via a loopback device) at the mount point
  /mnt.  A df will confirm this.



  After you've chosen one of these options, prepare the DEVICE with:

          dd if=/dev/zero of=DEVICE bs=1k count=3000



  This command zeroes out the device.  This step is important because
  the filesystem on the device will be compressed later, so all unused
  portions should be filled with zeroes to achieve maximum compression.

  Next, create the filesystem.  The Linux kernel recognizes two file
  system types for root disks to be automatically copied to ramdisk.
  These are minix and ext2, of which ext2 is the preferred file system.
  If using ext2, you may find it useful to use the -i option to specify
  more inodes than the default; -i 2000 is suggested so that you don't
  run out of inodes.  Alternatively, you can save on inodes by removing
  lots of unnecessary /dev files.  mke2fs will by default create 360
  inodes on a 1.44Mb diskette.  I find that 120 inodes is ample on my
  current rescue root diskette, but if you include all the devices in
  the /dev directory then you will easily exceed 360.  Using a
  compressed root filesystem allows a larger filesystem, and hence more
  inodes by default, but you may still need to either reduce the number
  of files or increase the number of inodes.

  So the command you use will look like:

       mke2fs -m 0 -i 2000 DEVICE


  (If you're using a loopback device, the disk file you're using should
  be supplied in place of this DEVICE.  mke2fs will ask if you really
  want to do this; say yes.)

  The mke2fs command will automatically detect the space available and
  configure itself accordingly.  The -m 0 parameter prevents it from
  reserving space for root, and hence provides more usable space on the
  disk.

  Next, mount the device:


          mount -t ext2 DEVICE /mnt



  (You must create a mount point /mnt if it does not already exist.)  In
  the remaining sections, all destination directory names are assumed to
  be relative to /mnt.



  4.3.  Populating the filesystem.


  Here is a reasonable minimum set of directories for your root
  filesystem:


  ∑  /dev --- Devices, required to perform I/O

  ∑  /proc --- Directory stub required by the proc filesystem

  ∑  /etc --- System configuration files

  ∑  /sbin --- Critical system binaries

  ∑  /bin  --- Basic binaries considered part of the system

  ∑  /lib --- Shared libraries to provide run-time support

  ∑  /mnt --- A mount point for maintenance on other disks

  ∑  /usr --- Additional utilities and applications

  (The directory structure presented here is for root diskette use only.
  Real Linux systems have a more complex and disciplined set of
  policies, called the File System Standard, for determining where files
  should go.)


  Three of these directories will be empty on the root filesystem, so
  they only need to be created with mkdir.  The /proc directory is
  basically a stub under which the proc filesystem is placed.  The
  directories /mnt and /usr are only mount points for use after the
  boot/root system is running.  Hence again, these directories only need
  to be created.

  The remaining four directories are described in the following
  sections.





  4.3.1.  /dev



  A /dev directory containing a special file for all devices to be used
  by the system is mandatory for any Linux system.  The directory itself
  is a normal directory, and can be created with mkdir in the normal
  way.  The device special files, however, must be created in a special
  way, using the mknod command.

  There is a shortcut, though --- copy your existing /dev directory
  contents, and delete the ones you don't want.  The only requirement is
  that you copy the device special files using -R option.  This will
  copy the directory without attempting to copy the contents of the
  files.  Be sure to use an upper case R.  If you use the lower case
  switch -r, you will probably end up copying the entire contents of all
  of your hard disks --- or at least as much of them as will fit on a
  diskette!  Therefore, take care, and use the command:


          cp -dpR /dev /mnt



  assuming that the diskette is mounted at /mnt.  The dp switches ensure
  that symbolic links are copied as links, rather than using the target
  file, and that the original file attributes are preserved, thus
  preserving ownership information.

  Alternatively, you can use the cpio program with the -p option,
  because cpio handles device special files correctly, and will not try
  to copy the contents.  For example, the commands:



       cd /dev
       find . -print | cpio -pmd /mnt/dev

  will copy all device special files from /dev to /mnt/dev.  In fact it
  will copy all files in the directory tree starting at /dev, and will
  create any required subdirectories in the target directory tree.

  If you want to do it the hard way, use ls -l to display the major and
  minor device numbers for the devices you want, and create them on the
  diskette using mknod.

  However the devices are copied, it is worth checking that any special
  devices you need have been placed on the rescue diskette.  For
  example, ftape uses tape devices, so you will need to copy all of
  these if you intend to access your floppy tape drive from the
  bootdisk.

  Note that one inode is required for each device special file, and
  inodes can at times be a scarce resource, especially on diskette
  filesystems.  It therefore makes sense to remove any device special
  files that you don't need from the diskette /dev directory.  Many
  devices are obviously unnecessary on specific systems.  For example,
  if you do not have SCSI disks you can safely remove all the device
  files starting with sd.  Similarly, if you don't intend to use your
  serial port then all device files starting with cua can go.

  Be sure to include the following files from this directory: console,
  kmem, mem, null, ram, tty1.


  4.3.2.  /etc


  This directory must contain a number of configuration files.  On most
  systems, these can be divided into three groups:


  1. Required at all times, e.g. rc, fstab, passwd.

  2. May be required, but no-one is too sure.

  3. Junk that crept in.

  Files which are not essential can be identified with the command:



               ls -ltru




  This lists files in reverse order of date last accessed, so if any
  files are not being accessed, they can be omitted from a root
  diskette.

  On my root diskettes, I have the number of config files down to 15.
  This reduces my work to dealing with three sets of files:


  1. The ones I must configure for a boot/root system:


     a. rc.d/* --- system startup and run level change scripts

     b. fstab --- list of file systems to be mounted

     c. inittab --- parameters for the init process, the first process
        started at boot time.
  2. The ones I should tidy up for a boot/root system:

     a. passwd --- list of users, home directories, etc.

     b. group --- user groups.

     c. shadow --- passwords of users.  You may not have this.


     If security is important, passwd and shadow should be pruned to
     avoid copying user passwords off the system, and so that when you
     boot from diskette, unwanted logins are rejected.  However, there
     is a reason not to prune passwd and group.  tar (and probably other
     archivers) stores user and group names with files.  If you restore
     files to your hard disk from tape, the files will be restored with
     their original names.  If these names do not exist in passwd/group
     when they are restored, the UIDs/GIDs will not be correct.

     Be sure that passwd contains at least root.  If you intend other
     users to login, be sure their home directories and shells exist.

  3. The rest. They work at the moment, so I leave them alone.

  Out of this, I only really have to configure two files, and what they
  should contain is surprisingly small.

  ∑  rc should contain:

             #!/bin/sh
             /bin/mount -av
             /bin/hostname Kangaroo



  Be sure the directories are right.  You don't really need to run host≠
  name --- it just looks nicer if you do.

  ∑  fstab should contain at least:


             /dev/ram0       /               ext2    defaults
             /dev/fd0        /               ext2    defaults
             /proc           /proc           proc    defaults



  You can copy entries from your existing fstab, but you should not
  automatically mount any of your hard disk partitions; use the noauto
  keyword with them.  Your hard disk may be damaged or dead when the
  bootdisk is used.

  Your inittab should be changed so that its sysinit line runs rc or
  whatever basic boot script will be used.  Also, if you want to ensure
  that users on serial ports cannot login, comment out all the entries
  for getty which include a ttys or ttyS device at the end of the line.
  Leave in the tty ports so that you can login at the console.

  A minimal inittab file looks like this:

          id:2:initdefault:
          si::sysinit:/etc/rc
          1:2345:respawn:/sbin/getty 9600 tty1
          2:23:respawn:/sbin/getty 9600 tty2



  The inittab file defines what the system will run in various states
  including startup, move to multi-user mode, etc.  A point to be
  careful of here is to carefully check that the commands entered in
  inittab refer to programs which are present and to the correct
  directory.  If you place your command files on your rescue disk using
  Section ``Sample rootdisk directory listings''  as a guide, and then
  copy your inittab to your rescue disk without checking it, the
  probability of failure will be quite high because half of the inittab
  entries will refer to missing programs or to the wrong directory.


  Note that some programs cannot be moved elsewhere because other
  programs have hardcoded their locations.  For example on my system,
  /etc/shutdown has hardcoded in it /etc/reboot.  If I move reboot to
  /bin/reboot, and then issue a shutdown command, it will fail because
  it cannot find the reboot file.


  For the rest, just copy all the text files in your /etc directory,
  plus all the executables in your /etc directory that you cannot be
  sure you do not need.  As a guide, consult the sample listing in
  Section ``Sample rootdisk directory listings''.  Probably it will
  suffice to copy only those files, but systems differ a great deal, so
  you cannot be sure that the same set of files on your system is
  equivalent to the files in the list.  The only sure method is to start
  with inittab and work out what is required.

  Most systems now use an /etc/rc.d/ directory containing shell scripts
  for different run levels.  The minimum is a single rc script, but it
  may be simpler just to copy inittab and the /etc/rc.d directory from
  your existing system, and prune the shell scripts in the rc.d
  directory to remove processing not relevent to a diskette system
  environment.


  4.3.3.  /bin and /sbin


  The /bin directory is a convenient place for extra utilities you need
  to perform basic operations, utilities such as ls, mv, cat and dd.
  See Appendix ``Sample rootdisk directory listings'' for an example
  list of files that go in a /bin and /sbin directories.  It does not
  include any of the utilities required to restore from backup, such as
  cpio, tar and gzip.  That is because I place these on a separate
  utility diskette, to save space on the boot/root diskette.  Once the
  boot/root diskette is booted, it is copied to the ramdisk leaving the
  diskette drive free to mount another diskette, the utility diskette.
  I usually mount this as /usr.

  Creation of a utility diskette is described below in the section
  Section ``Building a utility disk''.  It is probably desirable to
  maintain a copy of the same version of backup utilities used to write
  the backups so you don't waste time trying to install versions that
  cannot read your backup tapes.

  Make sure you include the following programs: init, getty or
  equivalent, login, mount, some shell capable of running your rc
  scripts, a link from sh to the shell.




  4.3.4.  /lib



  In /lib you place necessary shared libraries and loaders.  If the
  necessary libraries are not found in your /lib directory then the
  system will be unable to boot.  If you're lucky you may see an error
  message telling you why.

  Nearly every program requires at least the libc library, libc.so.N,
  where N is the current version number.  Check your /lib directory.
  libc.so.5 is usually a symlink to a filename with a complete version
  number:



       % ls -l /lib/libc.so*
       lrwxrwxrwx  1 root root      14 Nov  1 20:34 /lib/libc.so.5 -> libc.so.5.4.33*
       -rwxr-xr-x  1 root root  573176 Jun 12 02:05 /lib/libc.so.5.4.33*




  In this case, you want libc.so.5.4.33.  To find other libraries you
  should go through all the binaries you plan to include and check their
  dependencies with the ldd command.  For example:


          % ldd /sbin/mke2fs
                  libext2fs.so.2 => /lib/libext2fs.so.2
                  libcom_err.so.2 => /lib/libcom_err.so.2
                  libuuid.so.1 => /lib/libuuid.so.1
                  libc.so.5 => /lib/libc.so.5



  Each file on the right-hand side is required.  Keep in mind that the
  libraries listed may be symbolic links.

  In /lib you must also include a loader for the libraries.  or ld-
  linux.so (for ELF libraries).  not sure which you need, run the file
  command on the library.  For example:


          % file /lib/libc.so.5.4.33 /lib/libc.so.4.7.2
          /lib/libc.so.4.7.2: Linux/i386 demand-paged executable (QMAGIC), stripped
          /lib/libc.so.5.4.33: ELF 32-bit LSB shared object, Intel 386, version 1, stripped



  The QMAGIC indicates that 4.7.2 is for a.out libraries, and ELF
  indicates that 5.4.33 is for ELF.

  Copy the specific loader(s) you need to the root filesystem you're
  building.  Libraries and loaders should be checked carefully against
  the included binaries.  If the kernel cannot load a necessary library,
  the kernel will usually hang with no error message.


  4.4.  Modules.


  If you have a modular kernel, you must consider which modules you may
  want to load from your bootdisk after booting.  You might want to
  include ftape and zftape modules if your backup tapes are on floppy
  tape, modules for SCSI devices if you have them, and possibly modules
  for PPP or SLIP support if you want to access the net in an emergency.

  These modules may be placed in /lib/modules.  You should also include
  insmod, rmmod and lsmod.  Depending on whether you want to load
  modules automatically, you might also include modprobe, depmod and
  swapout.  If you use kerneld, include it along with /etc/conf.modules.

  However, the main advantage to using modules is that you can move non-
  critical modules to a utility disk and load them when needed, thus
  using less space on your root disk.  If you may have to deal with many
  different devices, this approach is preferable to building one huge
  kernel with many drivers built in.

  Note that in order to boot a compressed ext2 filesystem, you must have
  ramdisk and ext2 support built-in.  They cannot be supplied as
  modules.



  4.5.  Some final details.


  Some system programs, such as login, complain if the file
  /var/run/utmp and the directory /var/log do not exist.


          mkdir -p /mnt/var/{log,run}
          touch /mnt/var/run/utmp



  Finally, after you have set up all the libraries you need, run
  ldconfig to remake /etc/ld.so.cache on the root filesystem.  The cache
  tells the loader where to find the libraries.  To remake ld.so.cache,
  issue the following commands:


          chdir /mnt; chroot /mnt /sbin/ldconfig



  The chroot is necessary because ldconfig always remakes the cache for
  the root filesystem.


  4.6.  Wrapping it up.


  Once you have finished constructing the root filesystem, unmount it,
  copy it to a file and compress it:


          umount /mnt
          dd if=DEVICE bs=1k | gzip -v9 > rootfs.gz



  This may take several minutes.  When it finishes you will have a file
  rootfs.gz that is your compressed root filesystem.  You should check
  its size to make sure it will fit on a diskette; if it doesn't you'll
  have to go back and remove some files.  Section ``Reducing root
  filesystem size'' has some hints for reducing the size of the root
  filesystem.



  5.  Choosing a kernel.



  At this point you have a complete compressed root filesystem.  The
  next step is to build or select a kernel.  In most cases it would be
  possible to copy your current kernel and boot the diskette from that.
  However, there may be cases where you wish to build a separate one.

  One reason is size.  If you are building a single boot/root diskette,
  the kernel will be one of the largest files on the diskette so you
  will have to reduce the size of the kernel as much as possible.  If
  you are building a two-disk boot+root diskette, this is not a concern
  since the kernel will go on a separate disk.

  To reduce kernel size, build it with the minumum set of facilities
  necessary to support the desired system.  This means leaving out
  everything you don't need.  Networking is a good thing to leave out,
  as well as support for any disk drives and other devices which you
  don't need when running your boot/root system.  As stated before, your
  kernel must have ramdisk and ext2 support built into it.

  Having worked out a minimum set of facilities to include in a kernel,
  you then need to work out what to add back in.  Probably the most
  common uses for a boot/root diskette system would be to examine and
  restore a corrupted root file system, and to do this you may need
  kernel support.  For example, if your backups are all held on tape
  using Ftape to access your tape drive, then, if you lose your current
  root drive and drives containing Ftape, then you will not be able to
  restore from your backup tapes.  You will have to reinstall Linux,
  download and reinstall ftape, and then try to read your backups.

  The point here is that, whatever I/O support you have added to your
  kernel to support backups should also be added into your boot/root
  kernel.


  The procedure for actually building the kernel is described in the
  documentation that comes with the kernel.  It is quite easy to follow,
  so start by looking in /usr/src/linux.  Note that if you have trouble
  building a kernel, then you should probably not attempt to build
  boot/root systems anyway.  Remember to compress the kernel with ``make
  zImage''.



  6.  Putting them together: Making the disk(s).


  At this point you have a kernel and a compressed root filesystem.  If
  you are making a boot/root disk, check their sizes to make sure they
  will both fit on one disk.  If you are making a two disk boot+root
  set, check the root filesystem to make sure it will fit on a single
  diskette.

  You should decide whether to use LILO to boot the bootdisk kernel.
  The alternative is to copy the kernel directly to the diskette and
  boot without LILO.  The advantage of using LILO is that it enables you
  to supply some parameters to the kernel which may be necessary to
  initialize your hardware (Check the file /etc/lilo.conf on your
  system.  If it exists and has a line like ``append=...'', you probably
  need this feature).  The disadvantage of using LILO is that building
  the bootdisk is more complicated, and takes slightly more space.  You
  will have to set up a small separate filesystem, which we shall call
  the kernel filesystem, where you transfer the kernel and a few other
  files that LILO needs.


  If you are going to use LILO, read on; if you are going to transfer
  the kernel directly, skip ahead to the section ``Without using LILO''.
  6.1.  Transferring the kernel with LILO


  The first thing you must do is create a small configuration file for
  LILO.  It should look like this:


  ______________________________________________________________________
          boot      =/dev/fd0
          install   =/boot/boot.b
          map       =/boot/map
          read-write
          backup    =/dev/null
          compact
          image     = KERNEL
          label     = Bootdisk
          root      =/dev/fd0
  ______________________________________________________________________



  For an explanation of these parameters, see LILO's user documentation.
  You will probably also want to add an append=... line to this file
  from your hard disk's /etc/lilo.conf file.

  Save this file as bdlilo.conf.

  You now have to create a small filesystem, which we shall call a
  kernel filesystem, to distinguish it from the root filesystem.

  First, figure out how large the filesystem should be.  Take the size
  of your kernel in blocks (the size shown by ``ls -l KERNEL'' divided
  by 1024 and rounded up) and add 50.  Fifty blocks is approximately the
  space needed for inodes plus other files.  You can calculate this
  number exactly if you want to, or just use 50.  If you're creating a
  two-disk set, you may as well overestimate the space since the first
  disk is only used for the kernel anyway.  Call this number
  KERNEL_BLOCKS.

  Put a floppy diskette in the drive (for simplicity we'll assume
  /dev/fd0) and create an ext2 kernel filesystem on it:


          mke2fs -i 8192 -m 0 /dev/fd0 KERNEL_BLOCKS




  The ``-i 8192'' specifies that we want one inode per 8192 bytes.
  Next, mount the filesystem, remove the lost+found directory, and
  create dev and boot directories for LILO:


          mount /dev/fd0 /mnt
          rm -rf /mnt/lost+found
          mkdir /mnt/{boot,dev}



  Next, create devices /dev/null and /dev/fd0.  Instead of looking up
  the device numbers, you can just copy them from your hard disk using
  -R:


          cp -R /dev/{null,fd0} /mnt/dev

  LILO needs a copy of its boot loader, boot.b, which you can take from
  your hard disk.  It is usually kept in the /boot directory.


          cp /boot/boot.b /mnt/boot



  Finally, copy in the LILO configuration file you created in the last
  section, along with your kernel.  Both can be put in the root
  directory:


          cp bdlilo.conf KERNEL /mnt



  Everything LILO needs is now on the kernel filesystem, so you are
  ready to run it.  LILO's -r flag is used for installing the boot
  loader on some other root:


          lilo -v -C bdlilo.conf -r /mnt



  LILO should run without error, after which the kernel filesystem
  should look something like this:


  ______________________________________________________________________
  total 361
    1 -rw-r--r--   1 root     root          176 Jan 10 07:22 bdlilo.conf
    1 drwxr-xr-x   2 root     root         1024 Jan 10 07:23 boot/
    1 drwxr-xr-x   2 root     root         1024 Jan 10 07:22 dev/
  358 -rw-r--r--   1 root     root       362707 Jan 10 07:23 vmlinuz
  boot:
  total 8
    4 -rw-r--r--   1 root     root         3708 Jan 10 07:22 boot.b
    4 -rw-------   1 root     root         3584 Jan 10 07:23 map
  dev:
  total 0
    0 brw-r-----   1 root     root       2,   0 Jan 10 07:22 fd0
    0 crw-r--r--   1 root     root       1,   3 Jan 10 07:22 null
  ______________________________________________________________________



  Do not worry if the file sizes are slightly different from yours.

  Now leave the disk in the drive and go to section ``Setting the
  ramdisk word''.


  6.2.  Transferring the kernel without LILO.


  If you are not using LILO, transfer the kernel to the bootdisk with
  the dd command:


          % dd if=KERNEL of=/dev/fd0 bs=1k
          353+1 records in
          353+1 records out


  In this example, dd wrote 353 complete records + 1 partial record, so
  the kernel occupies the first 354 blocks of the diskette.  Call this
  number KERNEL_BLOCKS and remember it because you use it in the next
  section.

  Finally, set the root device to be the diskette itself, then set the
  root to be loaded read/write:


          rdev /dev/fd0 /dev/fd0
          rdev -R /dev/fd0 0




  Be careful to use a capital -R in the second rdev command.



  6.3.  Setting the ramdisk word.


  Inside the kernel image is the ramdisk word that specifies where the
  root filesystem is to be found, along with other options.  The word is
  defined in /usr/src/linux/arch/i386/kernel/setup.c and is interpreted
  as follows:


          bits  0-10:     Offset to start of ramdisk, in 1024 byte blocks
          bits 11-13:     unused
          bit     14:     Flag indicating that ramdisk is to be loaded
          bit     15:     Flag indicating to prompt before loading rootfs



  If bit 15 is set, on boot-up you will be prompted to place a new
  floppy diskette in the drive.  This is necessary for a two-disk boot
  set.

  There are two cases, depending on whether you are building a single
  boot/root diskette or a double ``boot+root'' diskette set.


  1. If you are building a single disk, the compressed root filesystem
     will be placed right after the kernel, so the offset will be the
     first free block (which should be the same as KERNEL_BLOCKS).  Bit
     14 will be set to 1, and bit 15 will be zero.

  2. If you are building a two-disk set, the root filesystem will begin
     at block zero of the second disk, so the offset will be zero.  Bit
     14 will be set to 1, and bit 15 will be 1.

  After carefully calculating the value for the ramdisk word, set it
  with rdev -r.  value.  If you used LILO, the argument to rdev here
  should be the mounted kernel path, e.g. /mnt/vmlinuz; if you copied
  the kernel with dd, instead use the floppy device name (e.g.,
  /dev/fd0).


          rdev -r KERNEL_OR_FLOPPY_DRIVE  VALUE



  If you used LILO, unmount the diskette now.


  6.4.  Transferring the root filesystem.


  The last step is to transfer the root filesystem.


  ∑  If the root filesystem will be placed on the same disk as the
     kernel, transfer it using dd with the seek option, which specifies
     how many blocks to skip:


             dd if=rootfs.gz of=/dev/fd0 bs=1k seek=KERNEL_BLOCKS



  ∑  If the root filesystem will be placed on a second disk, remove the
     first diskette, put the second diskette in the drive, then transfer
     the root filesystem to it:


             dd if=rootfs.gz of=/dev/fd0 bs=1k



  Congratulations, you are done!

  =====  You should always test a bootdisk before putting it aside for
  an emergency! =====


  7.  Troubleshooting, or The Agony of Defeat.



  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.  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 /rootdisk/bin instead of /bin on your
     root diskette.

  ∑  Check that there is a /lib/libc.so with the same link that appears
     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, /dev/null, /dev/zero,
     /dev/mem, /dev/ram and /dev/kmem files.


  ∑  Check your kernel configuration --- support for all resources
     required up to login point must be built in, not modules.  So
     ramdisk and ext2 support must be built-in.

  ∑  Check that your kernel root device and ramdisk settings are
     correct.

  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 is executable.

  2. Run ldd init to check init's libraries.  Usually this is just
     libc.so, but check anyway.  Make sure you included the necessary
     libraries and loaders.

  3. Make sure you have the right loader for your libraries --- ld.so
     for a.out or ld-linux.so for ELF.

  4. Check the /etc/inittab on your bootdisk filesystem for the calls to
     getty (or some getty-like program, such as agetty, mgetty or
     getty_ps).  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 to execute the system initialization
     script, which must exist.

  5. As with init, run ldd on your getty to see what it needs, and make
     sure the necessary library files and loaders were included in your
     root filesystem.

  6. Be sure you have included a shell program (e.g., bash or ash)
     capable of running all of your rc scripts.

  7. 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 5 minutes




  it is coming from init, usually indicating that getty or login is
  dying as soon as it starts up.  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 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, and
  (2) make sure you have libraries (and loaders) the program needs.



  8.  Miscellaneous topics.



  8.1.  Reducing root filesystem size.


  Sometimes a root filesystem is too large to fit on a diskette even
  after compression.  Here are some ways to reduce the filesystem size,
  listed in decreasing order of effectiveness:



     Increase the disk density
        By default, floppy diskettes are formatted at 1440K, but higher
        density formats are available.  fdformat will format disks for
        the following sizes: 1600, 1680, 1722, 1743, 1760, 1840, and
        1920.  Most 1440K drives will support 1722K, and this is what I
        always use for bootdisks.  See the fdformat man page and
        /usr/src/linux/Documentation/devices.txt.


     Replace your shell
        Some of the popular shells for Linux, such as bash and tcsh, are
        large and require many libraries.  Light-weight alternatives
        exist, such as ash, lsh, kiss and smash, which are much smaller
        and require few (or no) libraries.  Most of these replacement
        shells are available from
        <http://sunsite.unc.edu/pub/Linux/system/shells/>.  Make sure
        any shell you use is capable of running commands in all the rc
        files you include on your bootdisk.


     Strip libraries and binaries
        are typically unstripped (include debugging symbols).  Running
        'file' on these files will tell you 'not stripped' if so.  When
        copying binaries to your root filesystem, it is good practice to
        use:


                objcopy --strip-all FROM TO



     When copying libraries, use:


             objcopy --strip-debug FROM TO





     Move non-critical files to a utility disk
        If some of your binaries are not needed immediately to boot or
        login, you can move them to a utility disk.  See section
        ``Building a utility disk'' for details.  You may also consider
        moving modules to a utility disk as well.



  8.2.  Non-ramdisk root filesystems.




  Section ``Building a root filesystem'' gave instructions for building
  a compressed root filesystem which is loaded to ramdisk when the
  system boots.  This method has many advantages so it is commonly used.
  However, some systems with little memory cannot afford the RAM needed
  for this; for such cases a root filesystem can be built that is
  mounted directly instead of copied to ramdisk.

  Such filesystems are actually easier to build than compressed root
  filesystems because they can be built on a diskette rather than on
  some other device, and they do not have to be compressed.  We will
  outline the procedure as it differs from the instructions above.  If
  you choose to do this, keep in mind that you will have far less space
  available.


  1. Calculate how much space you will have available for root files.

     If you are building a single boot/root disk, you must fit all
     blocks for the kernel plus all blocks for the root filesystem on
     the one disk.

  2. Using mke2fs, create a root filesystem on a diskette of the
     appropriate size.

  3. Populate the filesystem as described above.

  4. When done, unmount the filesystem and transfer it to a disk file
     but do not compress it.

  5. Transfer the kernel to a floppy diskette, as described above.  When
     calculating the ramdisk word, set bit 14 to zero, to indicate that
     the root filesystem is not to be loaded to ramdisk.  Run the rdev's
     as described.

  6. Transfer the root filesystem as before.

  There are several shortcuts you can take.  If you are building a two-
  disk set, you can build the complete root filesystem directly on the
  second disk and you need not transfer it to a hard disk file and then
  back.  Also, if you are building a single boot/root disk and using
  LILO, you can build a single filesystem on the entire disk, containing
  the kernel, LILO files and root files, and simply run LILO as the last
  step.



  8.3.  Building a utility disk.



  Building a utility disk is relatively easy --- simply create a
  filesystem on a formatted disk and copy files to it.  To use it with a
  bootdisk, mount it manually after the system is booted.

  In the instructions above, we mentioned that the utility disk could be
  mounted as /usr.  In this case, binaries could be placed into a /bin
  directory on your utility disk, so that placing /usr/bin in your path
  will access them.  Additional libraries needed by the binaries are
  placed in /lib on the utility disk.

  There are several important points to keep in mind when designing a
  utility disk:


  1. Do not place critical system binaries or libraries onto the utility
     disk, since it will not be mountable until after the system has
     booted.

  2. You cannot access a floppy diskette and a floppy tape drive
     simultaneously.  This means that if you have a floppy tape drive,
     you will not be able to access it while your utility disk is
     mounted.

  3. Access to files on the utility disk will be slow.

  Appendix ``Sample utility disk directory listing'' shows a sample of
  files on a utility disk.  Here are some ideas for files you may find
  useful: programs for examining and manipulating disks (format, fdisk)
  and filesystems (mke2fs, fsck, isofs.o), a lightweight text editor
  (elvis, jove), compression and archive utilities (gzip, tar, cpio,
  afio), tape utilities (mt, tob, taper), communications utilities
  (ppp.o, slip.o, minicom) and utilities for devices (setserial, mknod).


  9.  How the pros do it.


  You may notice that the bootdisks used by major distributions such as
  Slackware, RedHat or Debian, seem more sophisticated than what is
  described in this document.  Professional distribution bootdisks are
  based on the same principles outlined here, but employ various tricks
  because their bootdisks have additional requirements.  First, they
  must be able to work with a wide variety of hardware, so they must be
  able to interact with the user and load various device drivers.
  Second, they must be prepared to work with many different installation
  options, with varying degrees of automation.  Finally, distribution
  bootdisks usually combine installation and rescue capabilities.

  Some bootdisks use a feature called initrd (initial ramdisk).  2.0.x
  and provides greater flexibility by allowing a kernel to boot in two
  phases.  When the kernel first boots, it loads an initial ramdisk
  image from the boot disk.  This initial ramdisk is a root filesystem
  containing a program that runs before the real root fs is loaded.
  This program usually inspects the environment and/or asks the user to
  select various boot options, such as the device from which to load the
  real rootdisk.  It typically loads additional modules not built in to
  the kernel.  When this initial program exits, the kernel loads the
  real root image and booting continues normally.  For further
  information on initrd, see /usr/src/linux/Documentation/initrd.txt and
  <ftp://elserv.ffm.fgan.de/pub/linux/loadlin-1.6/initrd-example.tgz>

  The following are summaries of how each distribution's installation
  disks seem to work, based on inspecting their filesystems and/or
  source code.  We do not guarantee that this information is completely
  accurate, or that they have not changed since the versions noted.

  Slackware (v.3.1) uses a straightforward LILO boot similar to what is
  described in section ``Transferring the kernel with LILO''.  The
  Slackware bootdisk prints a bootup message (``Welcome to the Slackware
  Linux bootkernel disk!'') using LILO's message parameter.  This
  instructs the user to enter a boot parameter line if necessary.  After
  booting, a root filesystem is loaded from a second disk.  The user
  invokes a setup script which starts the installation.  Instead of
  using a modular kernel, Slackware provides many different kernels and
  depends upon the user to select the one matching his or her hardware
  requirements.

  RedHat (v.4.0) also uses a LILO boot.  It loads a compressed ramdisk
  on the first disk, which runs a custom init program.  This program
  queries for drivers, and loads additional files from a supplemental
  disk if necessary.

  Debian (v.1.3) is probably the most sophisticated of the installation
  disk sets.  It uses the SYSLINUX loader to arrange various load
  options, then uses an initrd image to guide the user through
  installation.  It appears to use both a customized init and a
  customized shell.



  10.  Frequently asked question (FAQ) list.


  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 ``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.

  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?



  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?


  The easiest way is to copy the filesystem from the rootdisk back to
  the DEVICE you used (from section ``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 ``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?


  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:



       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
  ``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?


  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




  This parameter string can be supplied in several ways using LILO:


  ∑  By entering it on the command line every time the system is booted
     via LILO.  This is boring, though.

  ∑  By using the LILO ``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.

  ∑  By using the 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?


  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:

  ∑  Shutdown in some versions has /etc/reboot hardcoded, so 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 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.



  K.  Resources and pointers.


  In this section, vvv is used in package names in place of the version,
  to avoid referring here to specific versions.  When retrieving a
  package, always get the latest version unless you have good reasons
  for not doing so.


  K.1.  Pre-made bootdisks.


  These are sources for distribution bootdisks.  Please use one of the
  mirror sites to reduce the load on these machines.


  ∑  Slackware bootdisks
     <http://sunsite.unc.edu/pub/Linux/distributions/slackware/bootdsks.144/>
     and Slackware mirror sites
     <http://sunsite.unc.edu/pub/Linux/distributions/slackware/MIRRORS.TXT>

  ∑  RedHat bootdisks
     <http://sunsite.unc.edu/pub/Linux/distributions/redhat/current/i386/images/>
     and Red Hat mirror sites <http://www.redhat.com/ftp.html>

  ∑  Debian bootdisks <ftp://ftp.debian.org/pub/debian/stable/disks-
     i386> and Debian mirror sites
     <ftp://ftp.debian.org/debian/README.mirrors>

  In addition to the distribution bootdisks, the following rescue disk
  images are available.


  ∑  tomsrtbt, by Tom Oehser, is a single-disk boot/root disk based on
     kernel 2.0.33, with a large list of features and support programs.
     It supports IDE, SCSI, tape, network adaptors, PCMCIA and more.
     About 100 utility programs and tools are included for fixing and
     restoring disks.  The package also includes scripts for
     disassembling and reconstructing the images so that new material
     can be added if necessary.

     <http://www.toms.net/~toehser/rb/tomsrtbt-current.tar.gz>

     <http://sunsite.unc.edu/pub/Linux/system/recovery/>


  ∑  rescue02, by John Comyns, is a rescue disk based on kernel 1.3.84,
     with support for IDE and Adaptec 1542 and NCR53C7,8xx.  It uses ELF
     binaries but it has enough commands so that it can be used on any
     system.  There are modules that can be loaded after booting for all
     other SCSI cards.  It probably won't work on systems with 4 mb of
     ram since it uses a 3 mb ram disk.
     <http://sunsite.unc.edu/pub/Linux/system/recovery/rescue02.zip>


  ∑  resque_disk-2.0.22, by Sergei Viznyuk, is a full-featured boot/root
     disk based on kernel 2.0.22 with built-in support for IDE, many
     difference SCSI controllers, and ELF/AOUT.  Also includes many
     modules and useful utilities for repairing and restoring a hard
     disk.

     <http://sunsite.unc.edu/pub/Linux/system/recovery/resque_disk-
     vvv.tar.gz>


  ∑  cramdisk images, based on the 2.0.23 kernel, available for 4 meg
     and 8 meg machines.  They include math emulation and networking
     (PPP and dialin script, NE2000, 3C509), or support for the parallel
     port ZIP drive.  These diskette images will boot on a 386 with 4MB
     RAM.  MSDOS support is included so you can download from the net to
     a DOS partition.

     <http://sunsite.unc.edu/pub/Linux/system/recovery/images/>



  K.2.  Rescue packages.


  Several packages for creating rescue disks are available on
  sunsite.unc.edu.  With these packages you generally specify a set of
  files for inclusion and the software automates (to varying degrees)
  the creation of a bootdisk.  See
  <http://sunsite.unc.edu/pub/Linux/system/recovery/!INDEX.html> for
  more information.  Check the file dates carefully --- some of these
  packages have not been updated in several years and will not support
  the creation of a compressed root filesystem loaded into ramdisk.  To
  the best of our knowledge, Yard is the only package that will.



  K.3.  Graham Chapman's shell scripts


  Graham Chapman has written a set of scripts that may be useful as
  examples of how to create bootdisks.  In previous versions of this
  HOWTO the scripts appeared in an appendix, but they have been deleted
  from the documented and placed on a web page:

  <http://www.zeta.org.au/~grahamc/linux.html>

  You may find it convenient to use these scripts, but if so, read the
  instructions carefully --- for example, if you specify the wrong swap
  device, you will find your root filesystem has been throroughly and
  permanently erased.  Be sure you have it correctly configured before
  you use it!



  K.4.  LILO --- the Linux loader.


  Written by Werner Almesberger.  Excellent boot loader, and the
  documentation includes information on the boot sector contents and the
  early stages of the boot process.

  Ftp from
  <ftp://tsx-11.mit.edu/pub/linux/packages/lilo/lilo.vvv.tar.gz>.  It is
  also available on Sunsite and mirrors.


  K.5.  Linux FAQ and HOWTOs.


  These are available from many sources.  Look at the usenet newsgroups
  news.answers and comp.os.linux.announce.

  The FAQ is available from
  <http://sunsite.unc.edu/pub/Linux/docs/faqs/linux-faq> and the HOWTOs
  from  <http://sunsite.unc.edu/pub/Linux/docs/HOWTO>.

  Most documentation for Linux may be found at The Linux Documentation
  Project homepage <http://sunsite.unc.edu/LDP/>.

  If desperate, send mail to [e-mail] with the word
  ``help'' in the message, then follow the mailed instructions.



  K.6.  Ramdisk usage.


  An excellent description of the how the new ramdisk code works may be
  found with the documentation supplied with the Linux kernel.  See
  /usr/src/linux/Documentation/ramdisk.txt.  It is written by Paul
  Gortmaker and includes a section on creating a compressed ramdisk.



  K.7.  The Linux boot process.


  For more detail on the Linux boot process, here are some pointers:


  ∑  The Linux System Administrators' Guide has a section on booting,
     See  <http://sunsite.unc.edu/LDP/LDP/sag-0.5/node68.html>

  ∑  The LILO ``Technical overview''
     <http://sunsite.unc.edu/pub/Linux/system/boot/lilo/lilo-t-20.ps.gz>
     has the definitive technical, low-level description of the boot
     process, up to where the kernel is started.

  ∑  The source code is the ultimate guide.  Below are some kernel files
     related to the boot process.  If you have the Linux kernel source
     code, you can find these under /usr/src/linux on your machine;
     alternatively, Shigio Yamaguchi ([e-mail]) has a
     very nice hypertext kernel browser at
     <http://wafu.netgate.net/linux/>.



     arch/i386/boot/bootsect.S,setup.S
        Contain assembly code for the bootsector.


     arch/i386/boot/compressed/misc.c
        Contains code for uncompressing the kernel.


     arch/i386/kernel/
        Directory containing kernel initialization code.  setup.c
        contains the ramdisk word.

     drivers/block/rd.c
        Contains the ramdisk driver. The procedures rd_load and
        rd_load_image load blocks from a device into a ramdisk.  The
        procedure identify_ramdisk_image determines what kind of
        filesystem is found and whether it is compressed.





  L.  LILO boot error codes.


  Questions about these errors are asked so often on Usenet that we
  include them here as a public service.  This summary is excerpted from
  Werner Almsberger's LILO User Documentation, available at
  <ftp://lrcftp.epfl.ch:/pub/linux/local/lilo/lilo.u.19.ps.gz>.

  When LILO loads itself, it displays the word ``LILO''.  Each letter is
  printed before or after performing some specific action.  If LILO
  fails at some point, the letters printed so far can be used to
  identify the problem.



     (nothing)
        No part of LILO has been loaded.  LILO either isn't installed or
        the partition on which its boot sector is located isn't active.


     L  The first stage boot loader has been loaded and started, but it
        can't load the second stage boot loader.  The two-digit error
        codes indicate the type of problem. (See also section ``Disk
        error codes''.)  This condition usually indicates a media
        failure or a geometry mismatch (e.g. bad disk parameters)


     LI The first stage boot loader was able to load the second stage
        boot loader, but has failed to execute it. This can either be
        caused by a geometry mismatch or by moving /boot/boot.b without
        running the map installer.


     LIL
        The second stage boot loader has been started, but it can't load
        the descriptor table from the map file. This is typically caused
        by a media failure or by a geometry mismatch.


     LIL?
        The second stage boot loader has been loaded at an incorrect
        address. This is typically caused by a subtle geometry mismatch
        or by moving /boot/boot.b without running the map installer.


     LIL-
        The descriptor table is corrupt. This can either be caused by a
        geometry mismatch or by moving /boot/map without running the map
        installer.


     LILO
        All parts of LILO have been successfully loaded.



  If the BIOS signals an error when LILO is trying to load a boot image,
  the respective error code is displayed.  These codes range from 0x00
  through 0xbb.  See the LILO User Guide for an explanation of these.



  M.  Sample rootdisk directory listings.



  Here are the contents of Graham's root and utility diskettes.  These
  lists are provided as an example only of the files included to create
  a working system.  Graham has added some explanatory notes where it
  seemed useful.




















































  total 18
  drwxr-xr-x   2 root     root         1024 Jul 29 21:16 bin/
  drwxr-xr-x   2 root     root         9216 Jul 28 16:21 dev/
  drwxr-xr-x   3 root     root         1024 Jul 29 20:25 etc/
  drwxr-xr-x   2 root     root         1024 Jul 28 19:53 lib/
  drwxr-xr-x   2 root     root         1024 Jul 24 22:47 mnt/
  drwxr-xr-x   2 root     root         1024 Jul 24 22:47 proc/
  drwxr-xr-x   2 root     root         1024 Jul 28 19:07 sbin/
  drwxr-xr-x   2 root     root         1024 Jul 29 20:57 tmp/
  drwxr-xr-x   4 root     root         1024 Jul 29 21:35 usr/
  drwxr-xr-x   3 root     root         1024 Jul 28 19:52 var/

  /bin:
  total 713
  -rwxr-xr-x   1 root     bin          7737 Jul 24 22:16 cat*
  -rwxr-xr-x   1 root     bin          9232 Jul 24 22:48 chmod*
  -rwxr-xr-x   1 root     bin          8156 Jul 24 22:48 chown*
  -rwxr-xr-x   1 root     bin         19652 Jul 24 22:48 cp*
  -rwxr-xr-x   1 root     root         8313 Jul 29 21:16 cut*
  -rwxr-xr-x   1 root     bin         12136 Jul 24 22:48 dd*
  -rwxr-xr-x   1 root     bin          9308 Jul 24 22:48 df*
  -rwxr-xr-x   1 root     root         9036 Jul 29 20:24 dircolors*
  -rwxr-xr-x   1 root     bin          9064 Jul 24 22:48 du*
  -rwxr-x---   1 root     bin         69252 Jul 24 22:51 e2fsck*
  -rwxr-xr-x   1 root     bin          5361 Jul 24 22:48 echo*
  -rwxr-xr-x   1 root     bin          5696 Jul 24 22:16 hostname*
  -rwxr-xr-x   1 root     bin          6596 Jul 24 22:49 kill*
  -rwxr-xr-x   1 root     bin         10644 Jul 24 22:17 ln*
  -rwxr-xr-x   1 root     bin         13508 Jul 24 22:17 login*
  -rwxr-xr-x   1 root     bin         26976 Jul 24 22:17 ls*
  -rwxr-xr-x   1 root     bin          7416 Jul 24 22:49 mkdir*
  -rwxr-x---   1 root     bin         34596 Jul 24 22:51 mke2fs*
  -rwxr-xr-x   1 root     bin          6712 Jul 24 22:49 mknod*
  -rwxr-xr-x   1 root     bin         20304 Jul 24 22:17 more*
  -rwxr-xr-x   1 root     bin         24704 Jul 24 22:17 mount*
  -rwxr-xr-x   1 root     bin         12464 Jul 24 22:17 mv*
  -rwxr-xr-x   1 root     bin         20829 Jul 24 22:50 ps*
  -rwxr-xr-x   1 root     bin          9424 Jul 24 22:50 rm*
  -rwxr-xr-x   1 root     bin          4344 Jul 24 22:50 rmdir*
  -rwxr-xr-x   1 root     root       299649 Jul 27 14:12 sh*
  -rwxr-xr-x   1 root     bin          9853 Jul 24 22:17 su*
  -rwxr-xr-x   1 root     bin           380 Jul 27 14:12 sync*
  -rwxr-xr-x   1 root     bin         13620 Jul 24 22:17 umount*
  -rwxr-xr-x   1 root     root         5013 Jul 29 20:03 uname*

  /dev:
  total 0
  lrwxrwxrwx   1 root     root           10 Jul 24 22:34 cdrom -> /dev/sbpcd
  crw--w--w-   1 root     tty        4,   0 Jul 24 21:49 console
  brw-rw----   1 root     floppy     2,   0 Apr 28  1995 fd0
  lrwxrwxrwx   1 root     root            4 Jul 24 22:34 ftape -> rft0
  crw-rw-rw-   1 root     sys       10,   2 Jul 18  1994 inportbm
  crw-rw----   1 root     kmem       1,   2 Jul 28 16:21 kmem
  crw-rw----   1 root     kmem       1,   1 Jul 18  1994 mem
  lrwxrwxrwx   1 root     root            4 Jul 24 22:34 modem -> cua0
  lrwxrwxrwx   1 root     root            4 Jul 24 22:34 mouse -> cua1
  crw-rw-rw-   1 root     sys        1,   3 Jul 18  1994 null
  brw-rw----   1 root     disk       1,   1 Jul 18  1994 ram
  crw-rw----   1 root     disk      27,   0 Jul 18  1994 rft0
  brw-rw----   1 root     disk      25,   0 Jul 19  1994 sbpcd
  ***  I have only included devices for the SCSI partitions I use.
  ***  If you use IDE, then use /dev/hdxx instead.
  brw-rw----   1 root     disk       8,   0 Apr 29  1995 sda
  brw-rw----   1 root     disk       8,   6 Apr 29  1995 sda6
  brw-rw----   1 root     disk       8,   7 Apr 29  1995 sda7
  brw-rw----   1 root     disk       8,   8 Apr 29  1995 sda8
  lrwxrwxrwx   1 root     root            7 Jul 28 12:56 systty -> console
  ***  this link from systty to console is required
  crw-rw-rw-   1 root     tty        5,   0 Jul 18  1994 tty
  crw--w--w-   1 root     tty        4,   0 Jul 18  1994 tty0
  crw--w----   1 root     tty        4,   1 Jul 24 22:33 tty1
  crw--w----   1 root     tty        4,   2 Jul 24 22:34 tty2
  crw--w--w-   1 root     root       4,   3 Jul 24 21:49 tty3
  crw--w--w-   1 root     root       4,   4 Jul 24 21:49 tty4
  crw--w--w-   1 root     root       4,   5 Jul 24 21:49 tty5
  crw--w--w-   1 root     root       4,   6 Jul 24 21:49 tty6
  crw-rw-rw-   1 root     tty        4,   7 Jul 18  1994 tty7
  crw-rw-rw-   1 root     tty        4,   8 Jul 18  1994 tty8
  crw-rw-rw-   1 root     tty        4,   9 Jul 19  1994 tty9
  crw-rw-rw-   1 root     sys        1,   5 Jul 18  1994 zero

  /etc:
  total 20
  -rw-r--r--   1 root     root         2167 Jul 29 20:25 DIR_COLORS
  -rw-r--r--   1 root     root           20 Jul 28 12:37 HOSTNAME
  -rw-r--r--   1 root     root          109 Jul 24 22:57 fstab
  -rw-r--r--   1 root     root          271 Jul 24 22:21 group
  -rw-r--r--   1 root     root         2353 Jul 24 22:27 inittab
  -rw-r--r--   1 root     root            0 Jul 29 21:02 issue
  -rw-r--r--   1 root     root         2881 Jul 28 19:38 ld.so.cache
  ***  Lots of things get upset at boot time if ld.so.cache is missing, but
  ***  make sure that ldconfig is included and run from rc.x to
  ***  update it.
  -rw-r--r--   1 root     root           12 Jul 24 22:22 motd
  -rw-r--r--   1 root     root          606 Jul 28 19:25 passwd
  -rw-r--r--   1 root     root         1065 Jul 24 22:21 profile
  drwxr-xr-x   2 root     root         1024 Jul 29 21:01 rc.d/
  -rw-r--r--   1 root     root           18 Jul 24 22:21 shells
  -rw-r--r--   1 root     root          774 Jul 28 13:43 termcap
  -rw-r--r--   1 root     root          126 Jul 28 13:44 ttys
  -rw-r--r--   1 root     root            0 Jul 24 22:47 utmp

  /etc/rc.d:
  total 5
  *** I didn't bother with shutdown scripts - everthing runs on a
  *** ramdisk, so there's not much point shutting it down.
  -rwxr-xr-x   1 root     root         1158 Jul 24 22:23 rc.K*
  -rwxr-xr-x   1 root     root         1151 Jul 28 19:08 rc.M*
  -rwxr-xr-x   1 root     root          507 Jul 29 20:25 rc.S*

  /lib:
  total 588
  *** I have an ELF system, so I include the ELF loader ld-linux.so. if
  *** you are still on a.out, then you need ld.so. Use the file command to
  *** see which libraries you should include.
  lrwxrwxrwx   1 root     root           17 Jul 24 23:36 ld-linux.so.1 -> ld-linux.so.1.7.3*
  -rwxr-xr-x   1 root     root        20722 Aug 15  1995 ld-linux.so.1.7.3*
  lrwxrwxrwx   1 root     root           13 Jul 24 23:36 libc.so.5 -> libc.so.5.0.9*
  -rwxr-xr-x   1 root     root       562683 May 19  1995 libc.so.5.0.9*
  ***  Must include libtermcap
  lrwxrwxrwx   1 root     root           19 Jul 28 19:53 libtermcap.so.2 -> libtermcap.so.2.0.0*
  -rwxr-xr-x   1 root     root        11360 May 19  1995 libtermcap.so.2.0.0*

  /mnt:
  total 0

  /proc:
  total 0

  /sbin:
  total 191
  ***  I use Slackware, which uses agetty. Many systems use getty.
  ***  Check your /etc/inittab to see which it uses. Note that you
  ***  need (a)getty and login to be able to start doing much.
  -rwxr-xr-x   1 root     bin         11309 Jul 24 22:54 agetty*
  -rwxr-xr-x   1 root     bin          5204 Jul 24 22:19 halt*
  ***  Must have this to boot
  -rwxr-xr-x   1 root     bin         20592 Jul 24 22:19 init*
  -rwxr-xr-x   1 root     root        86020 Jul 28 19:07 ldconfig*
  -rwxr-xr-x   1 root     bin          5329 Jul 27 14:10 mkswap*
  -rwxr-xr-x   1 root     root         5204 Jul 24 22:20 reboot*
  -rwxr-xr-x   1 root     root         6024 Jul 24 22:20 rdev*
  -rwxr-xr-x   1 root     bin         12340 Jul 24 22:20 shutdown*
  -rwxr-xr-x   1 root     root         5029 Jul 24 22:20 swapoff*
  -rwxr-xr-x   1 root     bin          5029 Jul 24 22:20 swapon*
  -rwxr-xr-x   1 root     root        20592 Jul 27 18:18 telinit*
  -rwxr-xr-x   1 root     root         7077 Jul 24 22:20 update*

  /tmp:
  total 0

  /usr:
  total 2
  drwxr-xr-x   2 root     root         1024 Jul 29 21:00 adm/
  drwxr-xr-x   2 root     root         1024 Jul 29 21:16 lib/

  /usr/adm:
  total 0

  /usr/lib:
  total 0

  /var:
  total 1
  ***  Several things complained until I included this and
  ***  the /etc/rc.S code to initialise /var/run/utmp, but this
  ***  won't necessarily apply to your system.
  drwxr-xr-x   2 root     root         1024 Jul 28 19:52 run/

  /var/run:
  total 0





  N.  Sample utility disk directory listing.





















  total 579
  -rwxr-xr-x   1 root     root        42333 Jul 28 19:05 cpio*
  -rwxr-xr-x   1 root     root       103560 Jul 29 21:31 elvis*
  -rwxr-xr-x   1 root     root        56401 Jul 28 19:06 find*
  -rwxr-xr-x   1 root     root        29536 Jul 28 19:04 fdisk*
  -rw-r--r--   1 root     root       128254 Jul 28 19:03 ftape.o
  -rwxr-xr-x   1 root     root        17564 Jul 25 03:21 ftmt*
  -rwxr-xr-x   1 root     root        64161 Jul 29 20:47 grep*
  -rwxr-xr-x   1 root     root        45309 Jul 29 20:48 gzip*
  -rwxr-xr-x   1 root     root        23560 Jul 28 19:04 insmod*
  -rwxr-xr-x   1 root     root          118 Jul 28 19:04 lsmod*
  lrwxrwxrwx   1 root     root            5 Jul 28 19:04 mt -> mt-st*
  -rwxr-xr-x   1 root     root         9573 Jul 28 19:03 mt-st*
  lrwxrwxrwx   1 root     root            6 Jul 28 19:05 rmmod -> insmod*
  -rwxr-xr-x   1 root     root       104085 Jul 28 19:05 tar*
  lrwxrwxrwx   1 root     root            5 Jul 29 21:35 vi -> elvis*