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New HOWTO: The Linux Kernel HOWTO - page 5

Table of Contents

  • April 2, 2001
  4.  How to actually configure the kernel



  4.1.  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.



  4.2.  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 -



  4.3.  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.



  4.3.1.  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.



  4.3.2.  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.



  4.3.3.  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.



  4.3.4.  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.



  4.3.5.  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.



  4.3.6.  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.



  4.3.7.  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.



  4.3.8.  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'.



  4.3.8.1.  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.



  4.3.9.  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.



  4.3.10.  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/.



  4.3.11.  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.



  4.3.12.  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.



  4.4.  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.
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