New HOWTO: The Linux Kernel HOWTO - page 5
Table of Contents
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
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
4.3.2. Enhanced (MFM/RLL) disk and IDE disk/cdrom support (Block
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.
The configure script then asks if you wish to support the following
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
/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'.
126.96.36.199. But I don't know which filesystems I need!
Ok, type `mount'. The output will look something like this:
/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)
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.
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 (firstname.lastname@example.org) 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
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.