Purpose of this document
My experience with Linux and modules has been that the existing
documents fail to provide a satisfactory explanation as to how to
successfully set up Linux with modules configured and working. The
procedure explained in this document has been successfully used several
times, both on my own system and over the Internet to give directions
to somebody trying to get some feature to work which requires a driver
supplied only in module form.
My own system runs from a RedHat 4.1 distribution of Linux, and it was
on this setup that I developed the procedure. I have since successfully
installed it on systems running from various Slackware distributions, and
on one system running from a Debian distribution, and the necessary
procedure to correctly configure modules under Linux in all three is
documented herein.
Compiler Speed-up
If your machine has 16 or more Megabytes of RAM, there is a useful
speed-up that can be done, which is to permit the kernel to compile two or
modules in parallel. This will increase the load on the machine whilst the
kernel is being recompiled, but will reduce the time during which the
compilation will be taking place.
Before you can use this method, you need to check the amount of RAM
present in your machine, as if you set this too high, the compilation will
actually slow down. Experience has shown that the optimum value depends on
the amount of RAM in your system according to the following formula, at
least for systems with up to 32 Megabytes of RAM, although it may be a
little conservative for systems with larger amounts of RAM:
N = [RAM in Megabytes] / 8 + 1
For the benefit of those with a dislike of maths, the values for the
common amounts of RAM are as follows:
| RAM size |
Value to use |
| 16 Megs |
3 |
| 24 Megs |
4 |
| 32 Megs |
5 |
| 40 Megs |
6 |
| 48 Megs |
7 |
| 56 Megs |
8 |
| 64 Megs |
9 |
| 80 Megs |
11 |
| 96 Megs |
13 |
| 112 Megs |
15 |
| 128 Megs |
17 |
When you have decided on the correct number, edit the file
/usr/src/linux/Makefile and find the line that currently reads:
MAKE=make
Replace it with one reading:
MAKE=make -j N
where N is the number determined above.
Recompiling the kernel for modules
The kernel can be reconfigured to use modules for everything other than
the file system mounted as root (in most cases, this is the ext2 file
system).
However, there are certain items that appear to be difficult to set up
properly as modules, so I would recommend the following be compiled into
the kernel:
- Ethernet hardware drivers.
- SCSI CD-ROM drivers.
On the other hand, there are certain driver combinations that
ONLY work as modules, especially combinations of two or more of the
following group:
- A Parallel Printer,
- A Parallel Port drive, such as the IOMEGA ZipDrive or
JazzDrive, or the BackPack CD-ROM drive, and
- The PLIP Daemon.
You will need to decide what you are compiling into the kernel, and
what as modules, but should take the above points into consideration. The
actual choices are made during the compilation, by the second of the
following sequence of instructions:
cd /usr/src/linux
make menuconfig
make dep clean modules modules_install zImage
Having done that, the module dependencies need to be mapped out. This
is done with the following command:
depmod -a
The new kernel now needs to be inserted in the boot chain. I am
assuming the reader is using LILO for this purpose, since this is the only
loader I have any experience with.
I recommend that one does NOT automatically insert the newly compiled
kernel as the default Linux kernel since if it should fail, it is then
extremely difficult to recover one's Linux setup without doing a complete
reinstallation, which is not to be recommended. For this reason, I have
the following entry in my /etc/lilo.conf file:
image=/usr/src/linux/arch/i386/boot/zImage
label=new
alias=n
read-only
vga=ask
optional
This entry says that there is an OPTIONAL boot option (which will be
ignored if the image in question does not exist) which boots the file
/boot/newlinux if selected, and allows one to select the video mode
it is to be booted in.
Assuming the existence of the above entry in /etc/lilo.conf the
revised kernel is already correctly located at the end of compilation, and
it can be installed via the following command:
lilo
Having done that, the reader needs to follow the further steps relevant
to their selected distribution, as follows:
Configuring Debian or RedHat for Modules
Prior to carrying out the steps listed here, the steps listed in
Recompiling the kernel for modules are assumed to
have been carried out.
The Debian and RedHat distributions have identical boot procedures, so
also have identical procedures for configuring modules into them.
- Having logged in as root, use your favourite text editor to create
a new file called /etc/rc.d/init.d/modules.init with the following
contents therein:
# Modules initialisation.
#
# Start up the module auto-loading daemon.
/sbin/kerneld
# Mount all currently unmounted auto-mounted partitions.
/sbin/mount -a
- Having created the above file, perform the following steps whilst
logged on as root:
cd /etc/rc.d
chmod 755 init.d/*
cd rc3.d
ln -s ../init.d/modules.init 05modules.init
The system can now be rebooted, and on doing so, it will be found that
modules are fully implemented
Configuring other distributions for Modules
Prior to carrying out the steps listed here, the steps listed in
Recompiling the kernel for modules are assumed to
have been carried out.
The precice procedure for other distributions has not been ascertained,
but is probably one of the above. To determine which one, display a
directory of the contents of the /etc/rc.d directory, as follows:
cd /etc/rc.d
ls -l *.d rc.*
From this resulting display, you can select one of the following three
options:
- If this list includes a directory named init.d and some
directories with names matching rc?.d where the question mark is
replaced by single digits, and does NOT include a file with the
name rc.M, that distribution can be configured for modules by
following the procedure listed above for the Debian and
RedHat Distributions.
- If this list does not include a directory named init.d but
includes a file named rc.M then that distribution can be configured
for modules by following the procedure listed above for the Slackware distribution.
- If this list matches neither of the above criteria, then the
distribution has a boot script not covered by this HowTo. In that case,
you are invited to contact the author of this document for advice.
