  The Linux Kernel HOWTO
  Brian Ward, bri@cs.uchicago.edu
  v1.0, 5 June 1999

  This is a detailed guide to kernel configuration, compilation,
  upgrades, and troubleshooting for ix86-based systems.
  ______________________________________________________________________

  Table of Contents



  1. Introduction

     1.1 Read this first! (I mean it)
     1.2 A word on style

  2. Important questions and their answers

     2.1 What does the kernel do, anyway?
     2.2 Why would I want to upgrade my kernel?
     2.3 What kind of hardware do the newer kernels support?
     2.4 What version of gcc and libc do I need?
     2.5 What's a loadable module?
     2.6 How much disk space do I need?
     2.7 How long does it take?

  3. How to actually configure the kernel

     3.1 Getting the source
     3.2 Unpacking the source
     3.3 Configuring the kernel
        3.3.1 Kernel math emulation (Processor type and features)
        3.3.2 Enhanced (MFM/RLL) disk and IDE disk/cdrom support (Block Devices)
        3.3.3 Networking support (General Setup)
        3.3.4 System V IPC (General Setup)
        3.3.5 Processor family (Processor type and features)
        3.3.6 SCSI support
        3.3.7 Network device support
        3.3.8 Filesystems
           3.3.8.1 But I don't know which filesystems I need!
        3.3.9 Character devices
        3.3.10 Sound
        3.3.11 Other configuration options
        3.3.12 Kernel hacking
     3.4 Now what? (The Makefile)

  4. Compiling the kernel

     4.1 Cleaning and depending
     4.2 Compile time
     4.3 Other ``make''ables
     4.4 Installing the kernel

  5. Patching the kernel

     5.1 Applying a patch
     5.2 If something goes wrong
     5.3 Getting rid of the .orig files
     5.4 Other patches

  6. Additional packages

     6.1 kbd
     6.2 util-linux
     6.3 hdparm
     6.4 gpm

  7. Some pitfalls

     7.1 make clean
     7.2 Huge or slow kernels
     7.3 The parallel port doesn't work/my printer doesn't work
     7.4 Kernel doesn't compile
     7.5 New version of the kernel doesn't seem to boot
     7.6 You forgot to run LILO, or system doesn't boot at all
     7.7 It says `warning: bdflush not running'
     7.8 I can't get my IDE/ATAPI CD-ROM drive to work
     7.9 It says weird things about obsolete routing requests
     7.10 Firewalling not working in 1.2.0
     7.11 ``Not a compressed kernel Image file''
     7.12 Problems with console terminal after upgrade to 1.3.x
     7.13 Can't seem to compile things after kernel upgrade
     7.14 Increasing limits

  8. Note for upgrade to version 2.0.x, 2.2.x

  9. Modules

     9.1 Installing the module utilities
     9.2 Modules distributed with the kernel

  10. Tips and tricks

     10.1 Redirecting output of the make or patch commands
     10.2 Conditional kernel install
     10.3 Kernel updates

  11. Other relevant HOWTOs that might be useful

  12. Misc

     12.1 Author
     12.2 To do
     12.3 Contributions
     12.4 Copyright notice, License, and all that stuff


  ______________________________________________________________________

  1.  Introduction


  Should you read this document? Well, see if you've got any of the
  following symptoms:



  o  ``Arg! This wizzo-46.5.6 package says it needs kernel release
     2.8.193 and I still only have release 1.0.9!''

  o  There's a device driver in one of the newer kernels that you just
     gotta have

  o  You really have no idea at all how to compile a kernel

  o  ``Is this stuff in the README really the whole story?''

  o  You came, you tried, it didn't work

  o  You need something to give to people who insist on asking you to
     install their kernels for them


  1.1.  Read this first! (I mean it)

  Some of the examples in this document assume that you have GNU tar,
  find, and xargs. These are quite standard; this should not cause
  problems. It is also assumed that you know your system's filesystem
  structure; if you don't, it is critical that you keep a written copy
  of the mount command's output during normal system operation (or a
  listing of /etc/fstab, if you can read it). This information is
  important, and does not change unless you repartition your disk, add a
  new one, reinstall your system, or something similar.
  The latest ``production'' kernel version at the time of this writing
  was 2.2.9, meaning that the references and examples correspond to that
  release. Even though I try to make this document as version-
  independent as possible, the kernel is constantly under development,
  so if you get a newer release, it will inevitably have some
  differences. Again, this should not cause major problems, but it may
  create some confusion.


  There are two versions of the linux kernel source, ``production'' and
  ``development.'' Production releases are the even-minor-numbered
  releases; 1.2.x was production, 2.0.x is production, as well as 2.2.x.
  These kernels are considered to be the most stable, bug-free versions
  available at the time of release. The development kernels (2.1.x,
  2.3.x, etc) are meant as testing kernels, for people willing to test
  out new and possibly very buggy kernels. You have been warned.



  1.2.  A word on style

  Text that looks like this is either something that appears on your
  screen, a filename, or something that can be directly typed in, such
  as a command, or options to a command (if you're looking at a plain-
  text file, it doesn't look any different). Commands and other input
  are frequently quoted (with ` '), which causes the following classic
  punctuation problem: if such an item appears at the end of a sentence
  in quotes, people often type a `.' along with the command, because the
  American quoting style says to put the period inside of the quotation
  marks. Even though common sense (and unfortunately, this assumes that
  the one with the ``common sense'' is used to the so-called American
  style of quotation) should tell one to strip off the punctuation
  first, many people simply do not remember, so I will place it outside
  the quotation marks in such cases. In other words, when indicating
  that you should type ``make config'' I would write `make config', not
  `make config.'



  2.  Important questions and their answers



  2.1.  What does the kernel do, anyway?


  The Unix kernel acts as a mediator for your programs and your
  hardware.  First, it does (or arranges for) the memory management for
  all of the running programs (processes), and makes sure that they all
  get a fair (or unfair, if you please) share of the processor's cycles.
  In addition, it provides a nice, fairly portable interface for
  programs to talk to your hardware.


  There is certainly more to the kernel's operation than this, but these
  basic functions are the most important to know.



  2.2.  Why would I want to upgrade my kernel?


  Newer kernels generally offer the ability to talk to more types of
  hardware (that is, they have more device drivers), they can have
  better process management, they can run faster than the older
  versions, they could be more stable than the older versions, and they
  fix silly bugs in the older versions. Most people upgrade kernels
  because they want the device drivers and the bug fixes.



  2.3.  What kind of hardware do the newer kernels support?


  See the Hardware-HOWTO. Alternatively, you can look at the `config.in'
  file in the linux source, or just find out when you try `make config'.
  This shows you all hardware supported by the standard kernel
  distribution, but not everything that linux supports; many common
  device drivers (such as the PCMCIA drivers and some tape drivers) are
  loadable modules maintained and distributed separately.



  2.4.  What version of gcc and libc do I need?


  Linus recommends a version of gcc in the README file included with the
  linux source. If you don't have this version, the documentation in the
  recommended version of gcc should tell you if you need to upgrade your
  libc.  This is not a difficult procedure, but it is important to
  follow the instructions.



  2.5.  What's a loadable module?


  These are pieces of kernel code which are not linked (included)
  directly in the kernel. One compiles them separately, and can insert
  and remove them into the running kernel at almost any time. Due to its
  flexibility, this is now the preferred way to code certain kernel
  features. Many popular device drivers, such as the PCMCIA drivers and
  the QIC-80/40 tape driver, are loadable modules.



  2.6.  How much disk space do I need?


  It depends on your particular system configuration. First, the
  compressed linux source is nearly 14 megabytes large at version 2.2.9.
  Many sites keep this even after unpacking.  Uncompressed and built
  with a moderate configuration, it takes up another 67 MB.



  2.7.  How long does it take?

  With newer machines, the compilation takes dramatically less time than
  older ones; an AMD K6-2/300 with a fast disk can do a 2.2.x kernel in
  about four minutes. As for old Pentiums, 486s, and 386s, if you plan
  to compile one, be prepared to wait, possibly hours, days..

  If this troubles you, and you happen to have a faster machine around
  to compile on, you can build on the fast machines (assuming you give
  it the right parameters, that your ulilities are up-to-date, and so
  on), and then transfer the kernel image to the slower machine.



  3.  How to actually configure the kernel



  3.1.  Getting the source


  You can obtain the source via anonymous ftp from ftp.kernel.org in
  /pub/linux/kernel/vx.y, where x.y is the version (eg 2.2), and as
  mentioned before, the ones that end with an odd number are development
  releases and may be unstable.  It is typically labelled linux-
  x.y.z.tar.gz, where x.y.z is the version number. The sites also
  typically carry ones with a suffix of .bz2, which have been compressed
  with bzip2 (these files will be smaller and take less time to
  transfer).

  It's best to use ftp.xx.kernel.org where xx is your country code;
  examples being ftp.at.kernel.org for Austria, and ftp.us.kernel.org
  for the United States.



  3.2.  Unpacking the source


  Log in as or su to `root', and cd to /usr/src.  If you installed
  kernel source when you first installed linux (as most do), there will
  already be a directory called `linux' there, which contains the entire
  old source tree.  If you have the disk space and you want to play it
  safe, preserve that directory. A good idea is to figure out what
  version your system runs now and rename the directory accordingly. The
  command `uname -r' prints the current kernel version.  Therefore, if
  `uname -r' said `1.0.9', you would rename (with `mv') `linux' to
  `linux-1.0.9'.  If you feel mildly reckless, just wipe out the entire
  directory. In any case, make certain there is no `linux' directory in
  /usr/src before unpacking the full source code.


  Now, in /usr/src, unpack the source with `tar zxpvf linux-
  x.y.z.tar.gz' (if you've just got a .tar  file with no .gz at the end,
  `tar xpvf linux-x.y.z.tar' works.).  The contents of the source will
  fly by. When finished, there will be a new `linux' directory in
  /usr/src. cd to linux and look over the README  file.  There will be a
  section with the label `INSTALLING the kernel'.  Carry out the
  instructions when appropriate -- symbolic links that should be in
  place, removal of stale .o files, etc.

  If you have a .bz2 file and the bzip2 program (read about it at
  http://www.muraroa.demon.co.uk/), do this:


       bz2cat linux-x.y.z.tar.bz2 | tar xvf -



  3.3.  Configuring the kernel


  Note: Some of this is reiteration/clarification of a similar section
  in Linus' README file.


  The command `make config' while in /usr/src/linux starts a configure
  script which asks you many questions. It requires bash, so verify that
  bash is /bin/bash, /bin/sh, or $BASH.
  However, there are some much more pleasant alternatives to `make
  config' and you may very well find them easier and more comfortable to
  use.  `make menuconfig' is probably the most widely-used. Whatever you
  choose, it's best to get familiar with the interface because you may
  find yourself back at it sooner than you think.  For those ``running
  X,'' you can try `make xconfig' if you have Tk installed (`click-o-
  rama' - Nat). `make menuconfig' is for those who have (n)curses and
  would prefer a text-based menu. These interfaces have a rather clear
  advantage: If you goof up and make a wrong choice during
  configuration, it is simple to go back and fix it.


  The configuration options will appear in hierarchies with `make
  menuconfig' and `make xconfig'.


  You are ready to answer the questions, usually with `y' (yes) or `n'
  (no). Device drivers typically have an `m' option.  This means
  ``module,'' meaning that the system will compile it, but not directly
  into the kernel, but as a loadable module. A more comical way to
  describe it is as ``maybe.'' Some of the more obvious and non-critical
  options are not described here; see the section ``Other configuration
  options'' for short descriptions of a few others.  With `make
  menuconfig', the space bar toggles the selection.


  In 2.0.x and later, there is a `?' option, which provides a brief
  description of the configuration parameter. That information is likely
  to be the most up-to-date. Here are a listing of some of the important
  features, which hierarchy they are in, and brief description.



  3.3.1.  Kernel math emulation (Processor type and features)

  If you don't have a math coprocessor (you have a bare 386 or 486SX),
  you must say `y' to this. If you do have a coprocessor and you still
  say `y', don't worry too much -- the coprocessor is still used and the
  emulation ignored. For any halfway modern machine, the answer will be
  no, but don't worry if you say yes accidentally; if not needed, it is
  not used.



  3.3.2.  Enhanced (MFM/RLL) disk and IDE disk/cdrom support (Block
  Devices)


  You probably need to support this; it means that the kernel will
  support standard PC hard disks, which most people have. This driver
  does not include SCSI drives; they come later in the configuration.

  You will then be asked about the ``old disk-only'' and ``new IDE''
  drivers.  You want to choose one of them; the main difference is that
  the old driver only supports two disks on a single interface, and the
  new one supports a secondary interface and IDE/ATAPI cdrom drives. The
  new driver is 4k larger than the old one and is also supposedly
  ``improved,'' meaning that aside from containing a different number of
  bugs, it might improve your disk performance, especially if you have
  newer (EIDE-type) hardware.



  3.3.3.  Networking support (General Setup)


  In principle, you would only say `y' if your machine is on a network
  such as the internet, or you want to use SLIP, PPP, term, etc to dial
  up for internet access. However, as many packages (such as the X
  window system) require networking support even if your machine does
  not live on a real network, you should say `y'. Later on, you will be
  asked if you want to support TCP/IP networking; again, say `y' here if
  you are not absolutely sure.



  3.3.4.  System V IPC (General Setup)


  One of the best definitions of IPC (Interprocess Communication) is in
  the Perl book's glossary. Not surprisingly, some Perl programmers
  employ it to let processes talk to each other, as well as many other
  packages (DOOM, most notably), so it is not a good idea to say n
  unless you know exactly what you are doing.



  3.3.5.  Processor family (Processor type and features)

  (in older kernels: Use -m486 flag for 486-specific optimizations)


  Traditionally, this compiled in certain optimizations for a particular
  processor; the kernels ran fine on other chips, but the kernel was
  perhaps a bit larger. In newer kernels, however, this is no longer
  true, so you should enter the processor for which you are compiling
  the kernel. A ``386'' kernel will work on all machines.



  3.3.6.  SCSI support


  If you have SCSI devices, say `y'. You will be prompted for further
  information, such as support for CD-ROM, disks, and what kind of SCSI
  adapter you have. See the SCSI-HOWTO for greater detail.



  3.3.7.  Network device support


  If you have a network card, or you would like to use SLIP, PPP, or a
  parallel port adapter for connecting to the Internet, say `y'. The
  config script will prompt for which kind of card you have, and which
  protocol to use.



  3.3.8.  Filesystems


  The configure script then asks if you wish to support the following
  filesystems:


  Standard (minix) - Newer distributions don't create minix filesystems,
  and many people don't use it, but it may still be a good idea to
  configure this one. Some ``rescue disk'' programs use it, and still
  more floppies may have a minix filesystem, since the minix filesystem
  is less painful to use on a floppy.


  Second extended - This is the standard Linux filesystem. You almost
  definitely have one of these, and need to say `y'.


  msdos - If you want to use your MS-DOS hard disk partitions, or mount
  MS-DOS formatted floppy disks, say `y'.


  There are various other foreign operating system filesystem types
  available.


  /proc - (idea from Bell Labs, I guess). One doesn't make a proc
  filesystem on a disk; this is a filesystem interface to the kernel and
  processes. Many process listers (such as `ps') use it. Try `cat
  /proc/meminfo' or `cat /proc/devices' sometime.  Some shells (rc, in
  particular) use /proc/self/fd  (known as /dev/fd on other systems) for
  I/O. You should almost certainly say `y' to this; many important linux
  tools depend on it.


  NFS - If your machine lives on a network and you want to use
  filesystems which reside on other systems with NFS, say `y'.


  ISO9660 - Found on most CD-ROMs. If you have a CD-ROM drive and you
  wish to use it under Linux, say `y'.



  3.3.8.1.  But I don't know which filesystems I need!


  Ok, type `mount'. The output will look something like this:



           blah# mount
           /dev/hda1 on / type ext2 (defaults)
           /dev/hda3 on /usr type ext2 (defaults)
           none on /proc type proc (defaults)
           /dev/fd0 on /mnt type msdos (defaults)



  Look at each line; the word next to `type' is the filesystem type. In
  this example, my /  and /usr filesystems are second extended, I'm
  using /proc, and there's a floppy disk mounted using the msdos (bleah)
  filesystem.

  You can try `cat /proc/filesystems' if you have /proc currently
  enabled; it will list your current kernel's filesystems.

  The configuration of rarely-used, non-critical filesystems can cause
  kernel bloat; see the section on modules for a way to avoid this and
  the ``Pitfalls'' section on why a bloated kernel is undesirable.



  3.3.9.  Character devices


  Here, you enable the drivers for your printer (parallel printer, that
  is), busmouse, PS/2 mouse (many notebooks use the PS/2 mouse protocol
  for their built-in trackballs), some tape drives, and other such
  ``character'' devices. Say `y' when appropriate.


  Note: gpm is a program which allows the use of the mouse outside of
  the X window system for cut and paste between virtual consoles. It's
  fairly nice if you have a serial mouse, because it coexists well with
  X, but you need to do special tricks for others.



  3.3.10.  Sound


  If you feel a great desire to hear biff bark, say `y', and you can
  tell the configuration program all about your sound board. (A note on
  sound card configuration: when it asks you if you want to install the
  full version of the driver, you can say `n' and save some kernel
  memory by picking only the features which you deem necessary.)


  If you are serious about sound card support, have a look at both the
  free drivers at http://www.linux.org.uk/OSS/ and the commercial Open
  Sound System at http://www.opensound.com/.



  3.3.11.  Other configuration options

  Not all of the configuration options are listed here because they
  change too often or fairly self-evident (for instance, 3Com 3C509
  support to compile the device drive for this particular ethernet
  card).  There exists a fairly comprehensive list of all the options
  (plus a way to place them into the Configure script) in an effort
  started and maintained by Axel Boldt (boldt@math.ucsb.edu) and it's
  the online help. It's also available as one big file at the
  Documentation/Configure.help in your Linux kernel source tree as of
  version 2.0.



  3.3.12.  Kernel hacking


  >From Linus' README:

  the ``kernel hacking'' configuration details usually result in a
  bigger or slower kernel (or both), and can even make the kernel less
  stable by configuring some routines to actively try to break bad code
  to find kernel problems (kmalloc()).  Thus you should probably answer
  `n' to the questions for a ``production'' kernel.



  3.4.  Now what? (The Makefile)


  After you finish configuration, a message tells you that your kernel
  has been configured, and to ``check the top-level Makefile for
  additional configuration,'' etc.

  So, look at the Makefile. You probably will not need to change it, but
  it never hurts to look. You can also change its options with the
  `rdev' command once the new kernel is in place. If you're feel lost
  when you look at the file, then don't worry about it.



  4.  Compiling the kernel



  4.1.  Cleaning and depending


  When the configure script ends, it also tells you to `make dep' and
  (possibly) `clean'.  So, do the `make dep'. This insures that all of
  the dependencies, such the include files, are in place. It does not
  take long, unless your computer is fairly slow to begin with.  For
  older versions of the kernel, when finished, you should do a `make
  clean'.  This removes all of the object files and some other things
  that an old version leaves behind. In any case, do not forget this
  step before attempting to recompile a kernel.



  4.2.  Compile time


  After depending and cleaning, you may now `make bzImage' or `make
  bzdisk' (this is the part that takes a long time.).  `make bzImage'
  will compile the kernel, and leave a file in arch/i386/boot called
  `bzImage' (among other things). This is the new compressed kernel.
  `make bzdisk' does the same thing, but also places the new bzImage on
  a floppy disk which you hopefully put in drive ``A:''.  `bzdisk' is
  fairly handy for testing new kernels; if it bombs (or just doesn't
  work right), just remove the floppy and boot with your old kernel. It
  can also be a handy way to boot if you accidentally remove your kernel
  (or something equally as dreadful). You can also use it to install new
  systems when you just dump the contents of one disk onto the other
  (``all this and more! NOW how much would you pay?'').


  All even halfway reasonably recent kernels are compressed, hence the
  `bz' in front of the names. A compressed kernel automatically
  decompresses itself when executed.

  In older kernels, you don't have the option to build a bzImage; it was
  simply a zImage. That option is at the moment still available,
  however, given the code size of newer kernels, it is now more or less
  mandatory to build a bzImage because the older methods can't handle a
  kernel that's just too large.



  4.3.  Other ``make''ables


  `make mrproper' will do a more extensive `clean'ing.  It is sometimes
  necessary; you may wish to do it at every patch. `make mrproper' will
  also delete your configuration file, so you might want to make a
  backup of it (.config) if you see it as valuable.


  `make oldconfig' will attempt to configure the kernel from an old
  configuration file; it will run through the `make config' process for
  you. If you haven't ever compiled a kernel before or don't have an old
  config file, then you probably shouldn't do this, as you will most
  likely want to change the default configuration.


  See the section on modules for a description of `make modules'.



  4.4.  Installing the kernel

  After you have a new kernel that seems to work the way you want it to,
  it's time to install it. Most people use LILO (Linux Loader) for this.
  `make bzlilo' will install the kernel, run LILO on it, and get you all
  ready to boot, BUT ONLY if lilo is configured in the following way on
  your system: kernel is /vmlinuz, lilo is in /sbin, and your lilo
  config (/etc/lilo.conf) agrees with this.


  Otherwise, you need to use LILO directly. It's a fairly easy package
  to install and work with, but it has a tendency to confuse people with
  the configuration file.  Look at the config file (either
  /etc/lilo/config for older versions or /etc/lilo.conf for new
  versions), and see what the current setup is. The config file looks
  like this:



      image = /vmlinuz
          label = Linux
          root = /dev/hda1
          ...



  The `image =' is set to the currently installed kernel.  Most people
  use /vmlinuz. `label' is used by lilo to determine which kernel or
  operating system to boot, and `root' is the / of that particular
  operating system. Make a backup copy of your old kernel and copy the
  bzImage which you just made into place (you would say `cp bzImage
  /vmlinuz' if you use `/vmlinuz').  Then, rerun lilo -- on newer
  systems, you can just run `lilo', but on older stuff, you might have
  to do an /etc/lilo/install or even an /etc/lilo/lilo -C
  /etc/lilo/config.


  If you would like to know more about LILO's configuration, or you
  don't have LILO, get the newest version from your favorite ftp site
  and follow the instructions.


  To boot one of your old kernels off the hard disk (another way to save
  yourself in case you screw up the new kernel), copy the lines below
  (and including) `image = xxx' in the LILO config file to the bottom of
  the file, and change the `image = xxx' to `image = yyy', where `yyy'
  is the full pathname of the file you saved your backup kernel to.
  Then, change the `label = zzz' to `label = linux-backup' and rerun
  lilo. You may need to put a line in the config file saying `delay=x',
  where x is an amount in tenths of a second, which tells LILO to wait
  that much time before booting, so that you can interrupt it (with the
  shift key, for example), and type in the label of the backup boot
  image (in case unpleasant things happen).



  5.  Patching the kernel



  5.1.  Applying a patch


  Incremental upgrades of the kernel are distributed as patches. For
  example, if you have version 1.1.45, and you notice that there's a
  `patch46.gz' out there for it, it means you can upgrade to version
  1.1.46 through application of the patch. You might want to make a
  backup of the source tree first (`make clean' and then `cd /usr/src;
  tar zcvf old-tree.tar.gz linux' will make a compressed tar archive for
  you.).


  So, continuing with the example above, let's suppose that you have
  `patch46.gz' in /usr/src. cd to /usr/src  and do a `zcat patch46.gz |
  patch -p0' (or `patch -p0 < patch46' if the patch isn't compressed).
  You'll see things whizz by (or flutter by, if your system is that
  slow) telling you that it is trying to apply hunks, and whether it
  succeeds or not. Usually, this action goes by too quickly for you to
  read, and you're not too sure whether it worked or not, so you might
  want to use the -s flag to patch, which tells patch to only report
  error messages (you don't get as much of the ``hey, my computer is
  actually doing something for a change!'' feeling, but you may prefer
  this..). To look for parts which might not have gone smoothly, cd to
  /usr/src/linux  and look for files with a .rej extension. Some
  versions of patch (older versions which may have been compiled with on
  an inferior filesystem) leave the rejects with a # extension. You can
  use `find' to look for you;

      find .  -name '*.rej' -print


  prints all files who live in the current directory or any subdirecto-
  ries with a .rej extension to the standard output.


  If everything went right, do a `make clean', `config', and `dep' as
  described in sections 3 and 4.


  There are quite a few options to the patch command. As mentioned
  above, patch -s will suppress all messages except the errors. If you
  keep your kernel source in some other place than /usr/src/linux, patch
  -p1 (in that directory) will patch things cleanly. Other patch options
  are well-documented in the manual page.



  5.2.  If something goes wrong


  (Note: this section refers mostly to quite old kernels)


  The most frequent problem that used to arise was when a patch modified
  a file called `config.in' and it didn't look quite right, because you
  changed the options to suit your machine. This has been taken care of,
  but one still might encounter it with an older release.  To fix it,
  look at the config.in.rej  file, and see what remains of the original
  patch.  The changes will typically be marked with `+' and `-' at the
  beginning of the line. Look at the lines surrounding it, and remember
  if they were set to `y' or `n'. Now, edit config.in, and change `y' to
  `n' and `n' to `y' when appropriate. Do a
      patch -p0 < config.in.rej


  and if it reports that it succeeded (no fails), then you can continue
  on with a configuration and compilation. The config.in.rej file will
  remain, but you can get delete it.


  If you encounter further problems, you might have installed a patch
  out of order. If patch says `previously applied patch detected: Assume
  -R?', you are probably trying to apply a patch which is below your
  current version number; if you answer `y', it will attempt to degrade
  your source, and will most likely fail; thus, you will need to get a
  whole new source tree (which might not have been such a bad idea in
  the first place).


  To back out (unapply) a patch, use `patch -R' on the original patch.


  The best thing to do when patches really turn out wrong is to start
  over again with a clean, out-of-the-box source tree (for example, from
  one of the linux-x.y.z.tar.gz  files), and start again.



  5.3.  Getting rid of the .orig files


  After just a few patches, the .orig  files will start to pile up. For
  example, one 1.1.51 tree I had was once last cleaned out at 1.1.48.
  Removing the .orig files saved over a half a meg.

      find .  -name '*.orig' -exec rm -f {} ';'


  will take care of it for you. Versions of patch which use # for
  rejects use a tilde instead of .orig.

  There are better ways to get rid of the .orig files, which depend on
  GNU xargs:

      find .  -name '*.orig' | xargs rm


  or the ``quite secure but a little more verbose'' method:

      find . -name '*.orig' -print0 | xargs --null rm --



  5.4.  Other patches


  There are other patches (I'll call them ``nonstandard'') than the ones
  Linus distributes. If you apply these, Linus' patches may not work
  correctly and you'll have to either back them out, fix the source or
  the patch, install a new source tree, or a combination of the above.
  This can become very frustrating, so if you do not want to modify the
  source (with the possibility of a very bad outcome), back out the
  nonstandard patches before applying Linus', or just install a new
  tree. Then, you can see if the nonstandard patches still work. If they
  don't, you are either stuck with an old kernel, playing with the patch
  or source to get it to work, or waiting (possibly begging) for a new
  version of the patch to come out.


  How common are the patches not in the standard distribution? You will
  probably hear of them. I used to use the noblink patch for my virtual
  consoles because I hate blinking cursors (This patch is (or at least
  was) frequently updated for new kernel releases.). With most newer
  device drivers being developed as loadable modules, though, the
  frequecy of ``nonstandard'' patches is decreasing significantly.



  6.  Additional packages

  Your linux kernel has many features which are not explained in the
  kernel source itself; these features are typically utilized through
  external packages. Some of the most common are listed here.



  6.1.  kbd

  The linux console probably has more features than it deserves. Among
  these are the ability to switch fonts, remap your keyboard, switch
  video modes (in newer kernels), etc. The kbd package has programs
  which allow the user to do all of this, plus many fonts and keyboard
  maps for almost any keyboard, and is available from the same sites
  that carry the kernel source.



  6.2.  util-linux

  Rik Faith (faith@cs.unc.edu) put together a large collection of linux
  utilities which are, by odd coincidence, called util-linux. These are
  now maintained by Andries Brouwer (util-linux@math.uio.no).  Available
  via anonymous ftp from sunsite.unc.edu in /pub/Linux/system/misc, it
  contains programs such as setterm, rdev, and ctrlaltdel, which are
  relevant to the kernel. As Rik says, do not install without thinking;
  you do not need to install everything in the package, and it could
  very well cause serious problems if you do.



  6.3.  hdparm

  As with many packages, this was once a kernel patch and support
  programs.  The patches made it into the official kernel, and the
  programs to optimize and play with your hard disk are distributed
  separately.



  6.4.  gpm

  gpm stands for general purpose mouse. This program allows you to cut
  and paste text between virtual consoles and do other things with a
  large variety of mouse types.



  7.  Some pitfalls



  7.1.  make clean

  If your new kernel does really weird things after a routine kernel
  upgrade, chances are you forgot to make clean before compiling the new
  kernel. Symptoms can be anything from your system outright crashing,
  strange I/O problems, to crummy performance. Make sure you do a make
  dep, too.



  7.2.  Huge or slow kernels

  If your kernel is sucking up a lot of memory, is too large, and/or
  just takes forever to compile even when you've got your new
  Quadbazillium-III/4400 working on it, you've probably got lots of
  unneeded stuff (device drivers, filesystems, etc) configured. If you
  don't use it, don't configure it, because it does take up memory.  The
  most obvious symptom of kernel bloat is extreme swapping in and out of
  memory to disk; if your disk is making a lot of noise and it's not one
  of those old Fujitsu Eagles that sound like like a jet landing when
  turned off, look over your kernel configuration.


  You can find out how much memory the kernel is using by taking the
  total amount of memory in your machine and subtracting from it the
  amount of ``total mem'' in /proc/meminfo  or the output of the command
  `free'.



  7.3.  The parallel port doesn't work/my printer doesn't work

  Configuration options for PCs are: First, under the category `General
  Setup', select `Parallel port support' and `PC-style hardware'. Then
  under `Character devices', select `Parallel printer support'.

  Then there are the names. Linux 2.2 names the printer devices
  differently than previous releases. The upshot of this is that if you
  had an lp1 under your old kernel, it's probably an lp0 under your new
  one.  Use `dmesg' or look through the logs in /var/log to find out.



  7.4.  Kernel doesn't compile


  If it does not compile, then it is likely that a patch failed, or your
  source is somehow corrupt. Your version of gcc also might not be
  correct, or could also be corrupt (for example, the include files
  might be in error). Make sure that the symbolic links which Linus
  describes in the README are set up correctly. In general, if a
  standard kernel does not compile, something is seriously wrong with
  the system, and reinstallation of certain tools is probably necessary.


  In some cases, gcc can crash due to hardware problems. The error
  message will be something like ``xxx exited with signal 15'' and it
  will generally look very mysterious. I probably would not mention
  this, except that it happened to me once - I had some bad cache
  memory, and the compiler would occasionally barf at random. Try
  reinstalling gcc first if you experience problems. You should only get
  suspicious if your kernel compiles fine with external cache turned
  off, a reduced amount of RAM, etc.



  It tends to disturb people when it's suggested that their hardware has
  problems. Well, I'm not making this up. There is an FAQ for it -- it's
  at http://www.bitwizard.nl/sig11/.



  7.5.  New version of the kernel doesn't seem to boot


  You did not run LILO, or it is not configured correctly. One thing
  that ``got'' me once was a problem in the config file; it said `boot =
  /dev/hda1' instead of `boot = /dev/hda' (This can be really annoying
  at first, but once you have a working config file, you shouldn't need
  to change it.).



  7.6.  You forgot to run LILO, or system doesn't boot at all


  Ooops! The best thing you can do here is to boot off of a floppy disk
  or CDROM and prepare another bootable floppy (such as `make zdisk'
  would do).  You need to know where your root (/) filesystem is and
  what type it is (e.g. second extended, minix). In the example below,
  you also need to know what filesystem your /usr/src/linux source tree
  is on, its type, and where it is normally mounted.


  In the following example, / is /dev/hda1, and the filesystem which
  holds /usr/src/linux is /dev/hda3, normally mounted at /usr. Both are
  second extended filesystems. The working kernel image in
  /usr/src/linux/arch/i386/boot is called bzImage.


  The idea is that if there is a functioning bzImage, it is possible to
  use that for the new floppy. Another alternative, which may or may not
  work better (it depends on the particular method in which you messed
  up your system) is discussed after the example.


  First, boot from a boot/root disk combo or rescue disk, and mount the
  filesystem which contains the working kernel image:



      mkdir /mnt
      mount -t ext2 /dev/hda3 /mnt



  If mkdir tells you that the directory already exists, just ignore it.
  Now, cd to the place where the working kernel image was. Note that

  /mnt + /usr/src/linux/arch/i386/boot - /usr = /mnt/src/linux/arch/i386/boot


  Place a formatted disk in drive ``A:'' (not your boot or root disk!),
  dump the image to the disk, and configure it for your root filesystem:



      cd /mnt/src/linux/arch/i386/boot
      dd if=bzImage of=/dev/fd0
      rdev /dev/fd0 /dev/hda1


  cd to / and unmount the normal /usr filesystem:


      cd /
      umount /mnt



  You should now be able to reboot your system as normal from this
  floppy.  Don't forget to run lilo (or whatever it was that you did
  wrong) after the reboot!


  As mentioned above, there is another common alternative. If you
  happened to have a working kernel image in / (/vmlinuz for example),
  you can use that for a boot disk. Supposing all of the above
  conditions, and that my kernel image is /vmlinuz, just make these
  alterations to the example above: change /dev/hda3 to /dev/hda1 (the /
  filesystem), /mnt/src/linux to /mnt, and if=bzImage to if=vmlinuz. The
  note explaining how to derive /mnt/src/linux may be ignored.


  Using LILO with big drives (more than 1024 cylinders) can cause
  problems.  See the LILO mini-HOWTO or documentation for help on that.



  7.7.  It says `warning: bdflush not running'


  This can be a severe problem. Starting with a kernel release after 1.0
  (around 20 Apr 1994), a program called `update' which periodically
  flushes out the filesystem buffers, was upgraded/replaced. Get the
  sources to `bdflush' (you should find it where you got your kernel
  source), and install it (you probably want to run your system under
  the old kernel while doing this). It installs itself as `update' and
  after a reboot, the new kernel should no longer complain.



  7.8.  I can't get my IDE/ATAPI CD-ROM drive to work

  Strangely enough, lots of people cannot get their ATAPI drives
  working, probably because there are a number of things that can go
  wrong.

  If your CD-ROM drive is the only device on a particular IDE interface,
  it must be jumpered as ``master'' or ``single.'' Supposedly, this is
  the most common error.

  Creative Labs (for one) has put IDE interfaces on their sound cards
  now.  However, this leads to the interesting problem that while some
  people only have one interface to being with, many have two IDE
  interfaces built-in to their motherboards (at IRQ15, usually), so a
  common practice is to make the soundblaster interface a third IDE port
  (IRQ11, or so I'm told).

  This causes problems with linux in that versions 1.2.x don't support a
  third IDE interface (there is support in starting somewhere in the
  1.3.x series but that's development, remember, and it doesn't auto-
  probe). To get around this, you have a few choices.


  If you have a second IDE port already, chances are that you are not
  using it or it doesn't already have two devices on it. Take the ATAPI
  drive off the sound card and put it on the second interface. You can
  then disable the sound card's interface, which saves an IRQ anyway.

  If you don't have a second interface, jumper the sound card's
  interface (not the sound card's sound part) as IRQ15, the second
  interface. It should work.



  7.9.  It says weird things about obsolete routing requests


  Get new versions of the route program and any other programs which do
  route manipulation.  /usr/include/linux/route.h  (which is actually a
  file in /usr/src/linux) has changed.



  7.10.  Firewalling not working in 1.2.0

  Upgrade to at least version 1.2.1.



  7.11.  ``Not a compressed kernel Image file''

  Don't use the vmlinux file created in /usr/src/linux as your boot
  image; [..]/arch/i386/boot/bzImage is the right one.



  7.12.  Problems with console terminal after upgrade to 1.3.x

  Change the word dumb to linux in the console termcap entry in
  /etc/termcap. You may also have to make a terminfo entry.



  7.13.  Can't seem to compile things after kernel upgrade

  The linux kernel source includes a number of include files (the things
  that end with .h) which are referenced by the standard ones in
  /usr/include. They are typically referenced like this (where xyzzy.h
  would be something in /usr/include/linux):

      #include <linux/xyzzy.h>


  Normally, there is a link called linux in /usr/include to the
  include/linux directory of your kernel source
  (/usr/src/linux/include/linux in the typical system). If this link is
  not there, or points to the wrong place, most things will not compile
  at all. If you decided that the kernel source was taking too much room
  on the disk and deleted it, this will obviously be a problem. Another
  way it might go wrong is with file permissions; if your root has a
  umask which doesn't allow other users to see its files by default, and
  you extracted the kernel source without the p (preserve filemodes)
  option, those users also won't be able to use the C compiler. Although
  you could use the chmod command to fix this, it is probably easier to
  re-extract the include files. You can do this the same way you did the
  whole source at the beginning, only with an additional argument:


      blah# tar zxvpf linux.x.y.z.tar.gz linux/include



  Note: ``make config'' will recreate the /usr/src/linux link if it
  isn't there.



  7.14.  Increasing limits

  The following few example commands may be helpful to those wondering
  how to increase certain soft limits imposed by the kernel:

  echo 4096 > /proc/sys/kernel/file-max
  echo 12288 > /proc/sys/kernel/inode-max
  echo 300 400 500 > /proc/sys/vm/freepages



  8.  Note for upgrade to version 2.0.x, 2.2.x

  Kernel versions 2.0.x and 2.2.x introduced quite a bit of changes for
  kernel installation. The file Documentation/Changes in the 2.0.x
  source tree contains information that you should know when upgrading
  to either of these versions. You will most likely need to upgrade
  several key packages, such as gcc, libc, and SysVInit, and perhaps
  alter some system files, so expect this. Don't panic, though.



  9.  Modules

  Loadable kernel modules can save memory and ease configuration. The
  scope of modules has grown to include filesystems, ethernet card
  drivers, tape drivers, printer drivers, and more.



  9.1.  Installing the module utilities

  The module utilities are available from wherever you got your kernel
  source as modutils-x.y.z.tar.gz; choose the highest patchlevel x.y.z
  that is equal to or below that of your current kernel. Unpack it with
  `tar zxvf modutils-x.y.z.tar.gz', cd to the directory it creates
  (modutils-x.y.z), look over the README, and carry out its installation
  instructions (which is usually something simple, such as make
  install). You should now have the programs insmod, rmmod, ksyms,
  lsmod, genksyms, modprobe, and depmod in /sbin. If you wish, test out
  the utilities with the ``hw'' example driver in insmod; look over the
  INSTALL file in that subdirectory for details.

  insmod inserts a module into the running kernel. Modules usually have
  a .o extension; the example driver mentioned above is called
  drv_hello.o, so to insert this, one would say `insmod drv_hello.o'. To
  see the modules that the kernel is currently using, use lsmod. The
  output looks like this:

      blah# lsmod
      Module:        #pages:  Used by:
      drv_hello          1


  `drv_hello' is the name of the module, it uses one page (4k) of mem-
  ory, and no other kernel modules depend on it at the moment. To remove
  this module, use `rmmod drv_hello'. Note that rmmod wants a module
  name, not a filename; you get this from lsmod's listing. The other
  module utilities' purposes are documented in their manual pages.
  9.2.  Modules distributed with the kernel

  As of version 2.0.30, most of everything is available as a loadable
  modules. To use them, first make sure that you don't configure them
  into the regular kernel; that is, don't say y to it during `make
  config'.  Compile a new kernel and reboot with it. Then, cd to
  /usr/src/linux again, and do a `make modules'. This compiles all of
  the modules which you did not specify in the kernel configuration, and
  places links to them in /usr/src/linux/modules.  You can use them
  straight from that directory or execute `make modules_install', which
  installs them in /lib/modules/x.y.z, where x.y.z is the kernel
  release.


  This can be especially handy with filesystems. You may not use the
  minix or msdos filesystems frequently. For example, if I encountered
  an msdos (shudder) floppy, I would insmod
  /usr/src/linux/modules/msdos.o, and then rmmod msdos when finished.
  This procedure saves about 50k of RAM in the kernel during normal
  operation. A small note is in order for the minix filesystem: you
  should always configure it directly into the kernel for use in
  ``rescue'' disks.



  10.  Tips and tricks



  10.1.  Redirecting output of the make or patch commands


  If you would like logs of what those `make' or `patch' commands did,
  you can redirect output to a file. First, find out what shell you're
  running: `grep root /etc/passwd' and look for something like
  `/bin/csh'.


  If you use sh or bash,

      (command) 2>&1 | tee (output file)


  will place a copy of (command)'s output in the file `(output file)'.


  For csh or tcsh, use

      (command) |& tee (output file)



  For rc (Note: you probably do not use rc) it's

      (command) >[2=1] | tee (output file)



  10.2.  Conditional kernel install

  Other than using floppy disks, there are several methods of testing
  out a new kernel without touching the old one. Unlike many other Unix
  flavors, LILO has the ability to boot a kernel from anywhere on the
  disk (if you have a large (500 MB or above) disk, please read over the
  LILO documentation on how this may cause problems). So, if you add
  something similar to

      image = /usr/src/linux/arch/i386/boot/bzImage
          label = new_kernel


  to the end of your LILO configuration file, you can choose to run a
  newly compiled kernel without touching your old /vmlinuz (after run-
  ning lilo, of course). The easiest way to tell LILO to boot a new ker-
  nel is to press the shift key at bootup time (when it says LILO on the
  screen, and nothing else), which gives you a prompt.  At this point,
  you can enter `new_kernel' to boot the new kernel.

  If you wish to keep several different kernel source trees on your
  system at the same time (this can take up a lot of disk space; be
  careful), the most common way is to name them /usr/src/linux-x.y.z,
  where x.y.z is the kernel version. You can then ``select'' a source
  tree with a symbolic link; for example, `ln -sf linux-1.2.2
  /usr/src/linux' would make the 1.2.2 tree current. Before creating a
  symbolic link like this, make certain that the last argument to ln is
  not a real directory (old symbolic links are fine); the result will
  not be what you expect.



  10.3.  Kernel updates

  Russell Nelson (nelson@crynwr.com) summarizes the changes in new
  kernel releases. These are short, and you might like to look at them
  before an upgrade. They are available with anonymous ftp from
  ftp.emlist.com in pub/kchanges or through the URL

      http://www.crynwr.com/kchanges



  11.  Other relevant HOWTOs that might be useful


  o  Sound-HOWTO: sound cards and utilities

  o  SCSI-HOWTO: all about SCSI controllers and devices

  o  NET-2-HOWTO: networking

  o  PPP-HOWTO: PPP networking in particular

  o  PCMCIA-HOWTO: about the drivers for your notebook

  o  ELF-HOWTO: ELF: what it is, converting..

  o  Hardware-HOWTO: overview of supported hardware

  o  Module mini-HOWTO: more on kernel modules

  o  Kerneld mini-HOWTO: about kerneld

  o  BogoMips mini-HOWTO: in case you were wondering



  12.  Misc



  12.1.  Author


  The author and maintainer of the Linux Kernel-HOWTO is Brian Ward
  (bri@cs.uchicago.edu). Please send me any comments, additions,
  corrections (Corrections are, in particular, the most important to
  me.).


  You can take a look at my `home page' at one of these URLs:

      http://www.math.psu.edu/bri/
      http://blah.math.tu-graz.ac.at/~bri/



  Even though I try to be attentive as possible with mail, please
  remember that I get a lot of it every day, so it may take a little
  time to get back to you. Especially when emailing me with a question,
  please try extra hard to be clear and detailed in your message. If
  you're writing about non-working hardware (or something like that), I
  need to know what your hardware configureation is. If you report an
  error, don't just say ``I tried this but it gave an error;'' I need to
  know what the error was.  I would also like to know what versions of
  the kernel, gcc, and libc you're using. If you just tell me you're
  using this-or-that distribution, it won't tell me much at all. I don't
  care if you ask simple questions; remember, if you don't ask, you may
  never get an answer! I'd like to thank everyone who has given me
  feedback.

  If your question does not relate to the kernel, or is in some language
  that I don't understand, I may not answer.


  If you mailed me and did not get an answer within a resonable amount
  of time (three weeks or more), then chances are that I accidentally
  deleted your message or something (sorry). Please try again.


  I get a lot of mail about thing which are actually hardware problems
  or issues. That's OK, but please try to keep in mind that I'm not
  familiar with all of the hardware in the world. I use AMD processors,
  Adaptec and Sybios SCSI controllers, and IBM SCSI disks.


  Version -0.1 was written on October 3, 1994. This document is
  available in SGML, PostScript, TeX, roff, and plain-text formats.



  12.2.  To do

  The ``Tips and tricks'' section is a little small. I hope to expand on
  it with suggestions from others.

  So is ``Additional packages.''

  More debugging/crash recovery info needed.



  12.3.  Contributions

  A small part of Linus' README (kernel hacking options) is inclusive.
  (Thanks, Linus!)

  uc@brian.lunetix.de (Ulrich Callmeier): patch -s and xargs.

  quinlan@yggdrasil.com (Daniel Quinlan): corrections and additions in
  many sections.

  nat@nat@nataa.fr.eu.org (Nat Makarevitch): mrproper, tar -p, many
  other things

  boldt@math.ucsb.edu (Axel Boldt): collected descriptions of kernel
  configuration options on the net; then provided me with the list

  lembark@wrkhors.psyber.com (Steve Lembark): multiple boot suggestion

  kbriggs@earwax.pd.uwa.edu.au (Keith Briggs): some corrections and
  suggestions

  rmcguire@freenet.columbus.oh.us (Ryan McGuire): makeables additions

  dumas@excalibur.ibp.fr (Eric Dumas): French translation

  simazaki@ab11.yamanashi.ac.jp (Yasutada Shimazaki): Japanese
  translation

  jjamor@lml.ls.fi.upm.es (Juan Jose Amor Iglesias): Spanish translation

  mva@sbbs.se (Martin Wahlen): Swedish translation

  jzp1218@stud.u-szeged.hu (Zoltan Vamosi): Hungarian translation

  bart@mat.uni.torun.pl (Bartosz Maruszewski): Polish translation

  donahue@tiber.nist.gov (Michael J Donahue): typos, winner of the
  ``sliced bread competition''

  rms@gnu.ai.mit.edu (Richard Stallman): ``free'' documentation
  concept/distribution notice

  dak@Pool.Informatik.RWTH-Aachen.DE (David Kastrup): NFS thing

  esr@snark.thyrsus.com (Eric Raymond): various tidbits


  The people who have sent me mail with questions and problems have also
  been quite helpful.



  12.4.  Copyright notice, License, and all that stuff

  Copyright (C) Brian Ward, 1994-1999.

  Permission is granted to make and distribute copies of this manual
  provided the copyright notice and this permission notice are preserved
  on all copies.


  Permission is granted to copy and distribute modified versions of this
  manual under the conditions for verbatim copying, provided that the
  derived work is distributed under the terms of a permission notice
  identical to this one. Translations fall under the catagory of
  ``modified versions.''
  Warranty: None.


  Recommendations: Commercial redistribution is allowed and encouraged;
  however, it is strongly recommended that the redistributor contact the
  author before the redistribution, in the interest of keeping things
  up-to-date (you could send me a copy of the thing you're making while
  you're at it). Translators are also advised to contact the author
  before translating. The printed version looks nicer. Recycle.



