Linux kerneld mini-HOWTO

Linux kerneld mini-HOWTO

Henrik Storner

[email protected]

Copyright � 2000 by Linux Documentation Project
Revision History
Revision v2.0 22 May 2000
conversion from HTML to DocBook SGML.
_________________________________________________________________

Table of Contents
[1]About the kerneld mini-HOWTO

[2]Credits

[3]What is kerneld?

[4]Why do I want to use it ?
[5]Where can I pick up the necessary pieces ?

[6]How do I set it up?

[7]Trying out kerneld

[8]How does kerneld know what module to load?

[9]Block devices
[10]Character devices
[11]Network devices
[12]Binary formats
[13]Line disciplines (slip, cslip and ppp)
[14]Network protocol families (IPX, AppleTalk, AX.25)
[15]File systems

[16]Devices requiring special configuration

[17]char-major-10 : Mice, watchdogs and randomness
[18]Loading SCSI drivers: The scsi_hostadapter entry
[19]When loading a module isn't enough: The post-install entry

[20]Spying on kerneld
[21]Special kerneld uses
[22]Common problems and things that make you wonder

About the kerneld mini-HOWTO

This document explains how to install and use the automatic kernel
module loader "kerneld". The latest released version of this document
can be found at [23]the Linux Documentation Project
_________________________________________________________________

Credits

This document is based on an original HTML version 1.7 dated July 19,
1997 by Henrik Storner <[24][email protected]> and was revised
and translated to DocBook DTD by Gary Lawrence Murphy
<[25][email protected]> May 20, 2000.

The following people have contributed to this mini-HOWTO at some
point:

* Bjorn Ekwall [email protected]
* Ben Galliart [email protected]
* Cedric Tefft [email protected]
* Brian Miller [email protected]
* James C. Tsiao [email protected]

If you find errors in this document, please send email to
<[26][email protected]>. Your comments, encouragement and
suggestions are welcome and appreciated, and help ensure this guide
remains current and accurate.
_________________________________________________________________

What is kerneld?

The kerneld feature was introduced during the 1.3 development kernels
by Bjorn Ekwall. It allows kernel modules such as device drivers,
network drivers and filesystems to be loaded automatically when they
are needed, rather than having to do it manually with modprobe or
insmod.

And for the more amusing aspects, although these are not (yet ?)
integrated with the standard kernel:

* It can be setup to run a user-program instead of the default
screen blanker, thus letting you use any program as a
screen-saver.
* Similar to the screen-blanker support, you can also change the
standard console beep into something completely different.

kerneld consists of two components:

* Support in the Linux kernel for sending requests to a daemon
requesting a module for a certain task.
* A user-space daemon that can figure out what modules must be
loaded to fulfill the request from the kernel.

Both components must be working for the kerneld support to function;
it is not enough that only one or the other has been setup.
_________________________________________________________________

Why do I want to use it ?

There are some good reasons for using kerneld. The ones I will mention
are mine, others have other reasons.

* If you have to build kernels for several systems that only differ
slightly - different kind of network card, for instance - then you
can build a single kernel and some modules, instead of having to
build individual kernels for each system.
* Modules are easier for developers to test. You don't need to
reboot the system to load and unload the driver; this applies to
all modules, not just kerneld-loaded ones.
* It cuts down on the kernel memory usage leaving more memory
available for applications. Memory used by the kernel is never
swapped out, so if you have 100Kb worth of unused drivers compiled
into your kernel, they are simply wasting RAM.
* Some of the things I use, the ftape floppy-tape driver, for
instance, or iBCS, are only available as modules, but I don't want
to bother with loading and unloading them whenever I need them.
* People making Linux distributions don't have to build 284
different boot images: Each user loads the drivers he needs for
just his hardware. Most modern Linux distributions will detect
your hardware and will only load those modules actually required.

Of course, there are also reasons why you may not want to use it. If
you prefer to have just one kernel image file with all of your drivers
built in, you are reading the wrong document.
_________________________________________________________________

Where can I pick up the necessary pieces ?

The support in the Linux kernel was introduced with Linux 1.3.57. If
you have an earlier kernel version, you will need to upgrade if you
want the kerneld support. The current Linux kernel sources can be
found at most Linux FTP archive sites including:

* [27]Kernel.Org Archive
* [28]Metalab Linux Archive
* [29]TSX-11 at MIT

The user-space daemon is included with the modules package. These are
normally available from the same place as the kernel sources

Note: If you want to try module-loading with the latest development
kernels, you should use the newer modutils package and not the
modules. Always check the Documentation/Changes file in the kernel
sources for the minimum required version number for your kernel
image. Also see about the problems with modules and 2.1 kernels.
_________________________________________________________________

How do I set it up?

First get the necessary parts: A suitable kernel and the latest
modules package. Then you should install the module utilities as per
the instructions included in the package. Pretty simple: Just unpack
the sources and run make install. This compiles and installs the
following programs in /sbin: genksysm, insmod, lsmod, modprobe, depmod
and kerneld. I recommend you add some lines to your startup-scripts to
do some necessary setup whenever you boot Linux. Add the following
lines to your /etc/rc.d/rc.S file (if you are running Slackware), or
to /etc/rc.d/rc.sysinit if you are running SysVinit, i.e. Debian,
Corel, RedHat, Mandrake or Caldera:
# Start kerneld - this should happen very early in the
# boot process, certainly BEFORE you run fsck on filesystems
# that might need to have disk drivers autoloaded
if [ -x /sbin/kerneld ]
then
/sbin/kerneld
fi

# Your standard fsck commands go here
# And you mount command to mount the root fs read-write

# Update kernel-module dependencies file
# Your root-fs MUST be mounted read-write by now
if [ -x /sbin/depmod ]
then
/sbin/depmod -a
fi

These commands may already be installed in your SysV init scripts. The
first part starts kerneld itself. The second calls depmod -a at
startup to build a list of all available modules and analyzes their
inter-dependencies. The depmod map then tells kerneld if one module
needs to have another loaded before it will itself load.

Note: Recent versions of kerneld have an option to link with the
GNU gdbm library, libgdbm. If you enable this when building the
module utilities, kerneld will not start if libgdbm is not
available which may well be the case if you have /usr on a separate
partition and start kerneld before /usr is mounted. The recommended
solution is to move /usr/lib/libgdbm to /lib, or to link kerneld
statically.

Next, unpack the kernel sources, configure and build a kernel to your
liking. If you have never done this before, you should definitely read
the README file at the top level of the Linux sources. When you run
make xconfig to configure the kernel, you should pay attention to some
questions that appear early on:
Enable loadable module support (CONFIG_MODULES) [Y/n/?] Y

You need to select the loadable module support, or there will be no
modules for kerneld to load! Just say Yes.
Kernel daemon support (CONFIG_KERNELD) [Y/n/?] Y

This, of course, is also necessary. Then, a lot of the things in the
kernel can be built as modules - you will see questions like
Normal floppy disk support (CONFIG_BLK_DEV_FD) [M/n/y/?]

where you can answer with an M for "Module". Generally, only the
drivers necessary for you to boot up your system should be built into
the kernel; the rest can be built as modules.

Essential drivers

Essential drivers required to boot your system must be compiled into
the core kernel and cannot be loaded as modules. Typically this will
include the hard-disk driver and the driver for the root filesystem.
If you have a dual-boot machine and rely on files found in the foreign
partition, you must also compile support for that filesystem into the
core kernel.

When you have gone through the make config, compile and install the
new kernel and the modules with make dep clean bzlilo modules
modules_install.

Phew.

Compiling a Kernel Image: The make zImage command will stop short
of installing a kernel and will leave the new kernel image in the
file arch/i386/boot/zImage. To use this image, you will need to
copy it to where you keep your boot-image and install it manually
with LILO.

For more information about configuring, building and installing
your own kernel, check out the Kernel-HOWTO posted regularly to
comp.os.linux.answers, and available from [30]the Linux
Documentation Project and its mirrors.
_________________________________________________________________

Trying out kerneld

Now reboot with the new kernel. When the system comes back up, you can
run ps ax, and you should see a line for kerneld:
PID TTY STAT TIME COMMAND
59 ? S 0:01 /sbin/kerneld

One of the nice things with kerneld is that once you have the kernel
and the daemon installed, very little setup is needed. For a start,
try using one of the drivers that you built as a module; it is more
likely than not that it will work without further configuration. If I
build the floppy driver as a module, I could put a DOS floppy in the
drive and type
osiris:~ $ mdir a:
Volume in drive A has no label
Volume Serial Number is 2E2B-1102
Directory for A:/

binuti~1 gz 1942 02-14-1996 11:35a binutils-2.6.0.6-2.6.0.7.diff.gz
libc-5~1 gz 24747 02-14-1996 11:35a libc-5.3.4-5.3.5.diff.gz
2 file(s) 26689 bytes

The floppy driver works! It gets loaded automatically by kerneld when
I try to use the floppy disk.

To see that the floppy module is indeed loaded, you can run
/sbin/lsmod to list all currently loaded modules:
osiris:~ $ /sbin/lsmod
Module: #pages: Used by:
floppy 11 0 (autoclean)

The "(autoclean)" means that the module will automatically be removed
by kerneld when it has not been used for more than one minute. So the
11 pages of memory (= 44kB, one page is 4 kB) will only be used while
I access the floppy drive - if I don't use the floppy for more than a
minute, they are freed. Quite nice, if you are short of memory for
your applications!
_________________________________________________________________

How does kerneld know what module to load?

Although kerneld comes with builtin knowledge about the most common
types of modules, there are situations where kerneld will not know how
to handle a request from the kernel. This is the case with things like
CD-ROM drivers or network drivers, where there are more than one
possible module that can be loaded.

The requests that the kerneld daemon gets from the kernel is for one
of the following items:

* a block-device driver
* a character-device driver
* a binary format
* a tty line discipline
* a filesystem
* a network device
* a network service (e.g. rarp)
* a network protocol (e.g. IPX)

The kerneld determines what module should be loaded by scanning the
configuration file /etc/conf.modules[31][1]. There are two kinds of
entries in this file: Paths where the module-files are located, and
aliases assigning the module to be loaded for a given service. If you
don't have this file already, you could create it by running
/sbin/modprobe -c | grep -v '^path' /etc/conf.modules

If you want to add yet another path directive to the default paths,
you must include all the default paths as well, since a path directive
in /etc/conf.modules will replaceall the ones that modprobe knows by
default!

Normally you don't want to add any paths by your own, since the
built-in set should take care of all normal setups (and then some...),
I promise!

On the other hand, if you just want to add an alias or an option
directive, your new entries in /etc/conf.modules will be added to the
ones that modprobe already knows. If you should redefine an alias or
an option, your new entries in /etc/conf.modules will override the
built-in ones.
_________________________________________________________________

Block devices

If you run /sbin/modprobe -c, you will get a listing of the modules
that kerneld knows about, and what requests they correspond to. For
instance, the request that ends up loading the floppy driver is for
the block-device that has major number 2:
osiris:~ $ /sbin/modprobe -c | grep floppy
alias block-major-2 floppy

Why block-major-2 ? Because the floppy devices /dev/fd* use major
device 2 and are block devices:
osiris:~ $ ls -l /dev/fd0 /dev/fd1
brw-rw-rw- 1 root root 2, 0 Mar 3 1995 /dev/fd0
brw-r--r-- 1 root root 2, 1 Mar 3 1995 /dev/fd1
_________________________________________________________________

Character devices

Character devices are dealt with in a similar way. E.g. the ftape
floppy tape driver sits on major-device 27:
osiris:~ $ ls -lL /dev/ftape
crw-rw---- 1 root disk 27, 0 Jul 18 1994 /dev/ftape

However, kerneld does not by default know about the ftape driver - it
is not listed in the output from /sbin/modprobe -c. So to setup
kerneld to load the ftape driver, I must add a line to the kerneld
configuration file, /etc/conf.modules:
alias char-major-27 ftape
_________________________________________________________________

Network devices

You can also use the device name instead of the char-major-xxx or
block-major-yyy setup. This is especially useful for network drivers.
For example, a driver for an ne2000 netcard acting as eth0 would be
loaded with
alias eth0 ne

If you need to pass some options to the driver, for example to tell
the module about what IRQ the netcard is using, you must add an
"options" line:
options ne irq=5

This will cause kerneld to load the NE2000 driver with the command
/sbin/modprobe ne irq=5

Of course, the actual options available are specific to the module you
are loading.
_________________________________________________________________

Binary formats

Binary formats are handled in a similar way. Whenever you try to run a
program that the kernel does not know how to load, kerneld gets a
request for binfmt-xxx, where xxx is a number determined from the
first few bytes of the executable. So, the kerneld configuration to
support loading the binfmt_aout module for ZMAGIC (a.out) executables
is
alias binfmt-267 binfmt_aout

Since the magic number for ZMAGIC files is 267, if you check
/etc/magic, you will see the number 0413; keep in mind that /etc/magic
uses octal numbers where kerneld uses decimal, and octal 413 = decimal
267. There are actually three slightly different variants of a.out
executables (NMAGIC, QMAGIC and ZMAGIC), so for full support of the
binfmt_aout module we need
alias binfmt-264 binfmt_aout # pure executable (NMAGIC)
alias binfmt-267 binfmt_aout # demand-paged executable (ZMAGIC)
alias binfmt-204 binfmt_aout # demand-paged executable (QMAGIC)

a.out, Java and iBCS binary formats are recognized automatically by
kerneld, without any configuration.
_________________________________________________________________

Line disciplines (slip, cslip and ppp)

Line disciplines are requested with tty-ldisc-x, with x being usually
1 (for SLIP) or 3 (for PPP). Both of these are known by kerneld
automatically.

Speaking of ppp, if you want kerneld to load the bsd_comp data
compression module for ppp, then you must add the following two lines
to your /etc/conf.modules:
alias tty-ldisc-3 bsd_comp
alias ppp0 bsd_comp
_________________________________________________________________

Network protocol families (IPX, AppleTalk, AX.25)

Some network protocols can be loaded as modules as well. The kernel
asks kerneld for a protocol family (e.g. IPX) with a request for
net-pf-X where X is a number indicating what family is wanted. E.g.
net-pf-3 is AX.25, net-pf-4 is IPX and net-pf-5 is AppleTalk; These
numbers are determined by the AF_AX25, AF_IPX etc. definitions in the
linux source file include/linux/socket.h. So to autoload the IPX
module, you would need an entry like this in /etc/conf.modules:
alias net-pf-4 ipx

See [32]Common Problems for information about how you can avoid some
annoying boot-time messages related to undefined protocol families.
_________________________________________________________________

File systems

kerneld requests for filesystems are simply the name of the filesystem
type. A common use of this would be to load the isofs module for
CD-ROM filesystems, i.e. filesystems of type iso9660:
alias iso9660 isofs
_________________________________________________________________

Devices requiring special configuration

Some devices require a bit of extra configuration beyond the normal
aliasing of a device to a module.

* Character devices on major number 10: [33]The miscellaneous
devices
* [34]SCSI devices
* [35]Devices that require special initialization
_________________________________________________________________

char-major-10 : Mice, watchdogs and randomness

Hardware devices are usually identified through their major device
numbers, e.g. ftape is char-major-27. However, if you look through the
entries in /dev for char major 10, you will see that this is a bunch
of very different devices, including

* Mice of various sorts (bus mice, PS/2 mice)
* Watchdog devices
* The kernel random device
* APM (Advanced Power Management) interface

These devices are controlled by several different modules, not a
single one, and therefore the kerneld configuration for these misc.
devices use the major number and the minor number:
alias char-major-10-1 psaux # For PS/2 mouse
alias char-major-10-130 wdt # For WDT watchdog

You need a kernel version 1.3.82 or later to use this; earlier
versions do not pass the minor number to kerneld, making it impossible
for kerneld to figure out which of the misc. device modules to load.
_________________________________________________________________

Loading SCSI drivers: The scsi_hostadapter entry

Drivers for SCSI devices consist of a driver for the SCSI host adapter
(e.g. an Adaptec 1542), and a driver for the type of SCSI device you
use, e.g. a hard disk, a CD-ROM or a tape-drive. All of these can be
loaded as modules. However, when you want to access e.g. the CD-ROM
drive that is connected to the Adaptec card, the kernel and kerneld
only knows that it needs to load the sr_mod module in order to support
SCSI CD-ROM's; it does not know what SCSI controller the CD-ROM is
connected to, and hence does not know what module to load to support
the SCSI controller.

To resolve this, you can add an entry for the SCSI driver module to
your /etc/conf.modules that tells kerneld which of the many possible
SCSI controller modules it should load:
alias scd0 sr_mod # sr_mod for SCSI CD-ROM's ...
alias scsi_hostadapter aha1542 # ... need the Adaptec driver

This only works with kernel version 1.3.82 or later.

This works if you have only one SCSI controller. If you have more than
one, things become a little more difficult.

In general, you cannot have kerneld load a driver for a SCSI host
adapter, if a driver for another host adapter is already installed.
You must either build both drivers into your kernel (not as modules),
or load the modules manually.

Tip: There is a way that you can have kerneld load multiple SCSI
drivers. James Tsiao came up with this idea:

You can easily have kerneld load the second scsi driver by setting
up the dependency in your modules.dep by hand. You just need an
entry like:

/lib/modules/2.0.30/scsi/st.o: /lib/modules/2.0.30/scsi/aha1542.o

To have kerneld load the aha1542.o before it loads st.o. My machine
at home is set up almost exactly like the setup above, and it works
fine for all my secondary scsi devices, including tape, cd-rom, and
generic scsi devices. The drawback is that depmod -a can't
autodetect these dependencies, so the user needs to add them by
hand, and not run depmod -a on boot up. But once it is set up,
kerneld will autoload the aha1542.o just fine.

You should be aware, that this technique only works if you have
different kinds of SCSI devices on the two controllers, for example,
hard disks on one controller, and cd-rom drives, tapes or generic SCSI
devices on another.
_________________________________________________________________

When loading a module isn't enough: The post-install entry

Sometimes, just loading the module is not enough to get things
working. For instance, if you have your sound card compiled as a
module, it is often convenient to set a certain volume level. Only
problem is, the setting vanishes the next time the module is loaded.
Here is a neat trick from Ben Galliart (<[36][email protected]>):

The final solution required installing the [37]setmix package and
then adding the following line to my /etc/conf.modules:

post-install sound /usr/local/bin/setmix -f /etc/volume.conf

What this does is that after the sound module is loaded, kerneld runs
the command indicated by the post-install sound entry. So the sound
module gets configured with the command /usr/local/bin/setmix -f
/etc/volume.conf.

This may be useful for other modules as well, for example the lp
module can be configured with the tunelp program by adding
post-install lp tunelp options

For kerneld to recognize these options, you will need a version of
kerneld that is 1.3.69f or later.

Note: An earlier version of this mini-HOWTO mentioned a pre-remove
option, that might be used to run a command just before kerneld
removed a module. However, this has never worked and its use is
therefore discouraged - most likely, this option will disappear in
a future kerneld release. The whole issue of module settings is
undergoing some change at the moment, and may look different on
your system by the time you read this.
_________________________________________________________________

Spying on kerneld

If you have tried everything, and just cannot figure out what the
kernel is asking kerneld to do, there is a way of seeing the requests
that kerneld receives, and hence to figure out what should go into
/etc/conf.modules: The kdstat utility.

This nifty little program comes with the modules-package, but it is
not compiled or installed by default. To build it, go to the directory
where you have the kerneld sources and type make kdstat. Then, to make
kerneld display information about what it is doing, run kdstat debug
and kerneld will start spewing messages on the console about what it
is doing. If you then try and run the command that you want to use,
you will see the kerneld requests; these can be put into
/etc/conf.modules and aliased to the module needed to get the job
done.

To turn off the debugging, run /sbin/kdstat nodebug.
_________________________________________________________________

Special kerneld uses

I knew you would ask about how to setup the screen-saver module!

The kerneld/GOODIES directory in modules package has a couple of
kernel patches for screen-saver and console-beep support in kerneld;
these are not yet part of the official kernel, so you will need to
install the kernel-patches and rebuild the kernel.

To install a patch, you use the patch command:
cd /usr/src/linux
patch -s -p1 /usr/src/modules-*/kerneld/GOODIES/blanker_patch

Then rebuild and install the new kernel.

When the screen-saver triggers, kerneld will run the command
/sbin/screenblanker; this file may be anything you like, for example,
a shell script that runs your favorite screen-saver.

When the kernel wants to unblank the screen, it sends a SIGQUIT signal
to the process running /sbin/screenblanker. Your shell script or
screen-saver should trap this, and terminate. Remember to restore the
screen to the original text mode!
_________________________________________________________________

Common problems and things that make you wonder

1. [38]Why do I get Cannot locate module for net-pf-X messages when I
run /sbin/ifconfig?

2. [39]After starting kerneld, my system slows to a crawl when I
activate my ppp-connection

3. [40]kerneld does not load my SCSI driver!
4. [41]modprobe complains about gcc2_compiled being undefined
5. [42]My sound driver keeps forgetting its settings for volume etc
6. [43]DOSEMU needs some modules; how can I get kerneld to load those
?

7. [44]Why do I get Ouch, kerneld timed out, message failed messages ?
8. [45]Mount doesn't wait for kerneld to load the filesystem module
9. [46]kerneld fails to load the ncpfs module
10. [47]kerneld fails to load the smbfs module
11. [48]I built everything as modules, and now my system cannot boot
or kerneld fails to load the root filesystem module!

12. [49]kerneld will not load at boot time; it complains about libgdbm
13. [50]I get Cannot load module xxx but I just reconfigured my kernel
without xxx support!

14. [51]I rebuilt my kernel and modules, and still get messages about
unresolved symbols when booting

15. [52]I installed Linux 2.1/2.3 and now I cannot load any modules!
16. [53]What about dial-on-demand networking?

1. Why do I get Cannot locate module for net-pf-X messages when I run
/sbin/ifconfig?

Around kernel version 1.3.80, the networking code was changed to allow
loading protocol families (e.g. IPX, AX.25 and AppleTalk) as modules.
This caused the addition of a new kerneld request: net-pf-X, where X
is a number identifying the protocol (see
/usr/src/linux/include/linux/socket.h for the meaning of the various
numbers). Unfortunately, ifconfig accidentally triggers these
messages, so a lot of people get a couple of messages logged when the
system boots and it runs ifconfig to setup the loopback device. The
messages are harmless, and you can disable them by adding the lines
alias net-pf-3 off # Forget AX.25
alias net-pf-4 off # Forget IPX
alias net-pf-5 off # Forget AppleTalk

to /etc/conf.modules. Of course, if you do use IPX as a module, you
should not add a line to disable IPX.

2. After starting kerneld, my system slows to a crawl when I activate
my ppp-connection

There have been a couple of reports of this. It seems to be an
unfortunate interaction between kerneld and the tkPPP script that is
used on some systems to setup and monitor the PPP connection. The
script apparently runs loops while running ifconfig. This triggers
kerneld, to look for the net-pf-X modules (see above), keeping the
system load high and possibly pouring lots of Cannot locate module for
net-pf-X messages into the system log. There is no known workaround,
other than not use tkPPP, or change it to use some other way of
monitoring the connection.

3. kerneld does not load my SCSI driver!

Add an entry for the SCSI hostadapter to your /etc/conf.modules. See
the description of the [54]scsi_hostadapter entry above.

4. modprobe complains about gcc2_compiled being undefined

This is a bug in the module utilities, that show up only with binutils
2.6.0.9 and later, and it is also documented in the release note for
the binutils. So read that, or fetch an upgrade to the
module-utilities that fix this bug.

5. My sound driver keeps forgetting its settings for volume etc

The settings for a module are stored inside the module itself when it
is loaded. So when kerneld auto-unloads a module, any settings you
have made are forgotten, and the next time the module loads it reverts
to the default settings.

You can tell kerneld to configure a module by running a program after
the module has been auto-loaded. See [55]Pre/Post Install on the
post-install entry.

6. DOSEMU needs some modules; how can I get kerneld to load those ?

You cannot. None of the dosemu versions, official or development
versions, support loading the dosemu modules through kerneld. However,
if you are running kernel 2.0.26 or later, you do not need the special
dosemu modules any longer; just upgrade dosemu to 0.66.1 or higher.

7. Why do I get Ouch, kerneld timed out, message failed messages ?

When the kernel sends a request off to to kerneld, it expects to
receive an acknowledgment back within one second. If kerneld does not
send this acknowledgment, this message is logged. The request is
retransmitted, and should get through eventually.

This usually happens on systems with a very high load. Since kerneld
is a user-mode process, it is scheduled just like any other process on
the system. At times of high load, it may not get to run in time to
send back the acknowledgment before the kernel times out.

If this happens even when the load is light, try restarting kerneld.
Kill the kerneld process, and start it again with the command
/usr/sbin/kerneld. If the problem persists, you should mail a bug
report to <[56][email protected]>, but please make sure
that your versions of the kernel, kerneld and the module utilities are
up-to-date before posting about the problem. Check the requirements in
linux/Documentation/Changes

8. Mount doesn't wait for kerneld to load the filesystem module

There has been a number of reports that the mount(8) command does not
wait for kerneld to load the filesystem module. lsmod does show that
kerneld loads the module, and if you repeat the mount command
immediately it will succeed. This appears to be a bug in the
module-utilities version 1.3.69f that affects some Debian users. It
can be fixed by getting a later version of the module-utilities.

9. kerneld fails to load the ncpfs module

You need to compile the ncpfs utilities with -DHAVE_KERNELD. See the
ncpfs Makefile.

10. kerneld fails to load the smbfs module

You are using an older version of the smbmount utilities. Get the
latest version (0.10 or later) from [57]the SMBFS archive one TSX-11

11. I built everything as modules, and now my system cannot boot or
kerneld fails to load the root filesystem module!

You cannot modularize everything: The kernel must have enough drivers
built in for it to be able to mount your root filesystem, and run the
necessary programs to start kerneld[58][2]. You cannot modularize

* the driver for the hard disk where your root filesystem lives
* the root filesystem driver itself
* the binary format loader for init, kerneld and other programs

12. kerneld will not load at boot time; it complains about libgdbm

Newer versions of kerneld need the GNU dbm library, libgdbm.so, to
run. Most installations have this file in /usr/lib, but you are
probably starting kerneld before the /usr filesystem is mounted. One
symptom of this is that kerneld will not start during boot-up (from
your rc-scripts), but runs fine if you start it by hand after that
system is up. The solution is to either move the kerneld startup to
after your /usr is mounted, or move the gdbm library to your root
filesystem, e.g. to /lib.

13. I get Cannot load module xxx but I just reconfigured my kernel
without xxx support!

The Slackware installation (possibly others) builds a default
/etc/rc.d/rc.modules which does an explicit modprobe on a variety of
modules. Exactly which modules get modprobed depends on the original
kernel's configuration. You have probably reconfigured your kernel to
exclude one or more of the modules that is getting modprobed in
rc.modules, thus, the error message(s). Update your rc.modules by
commenting out any modules you no longer use, or remove the rc.modules
entirely and let kerneld load the modules when they are needed.

14. I rebuilt my kernel and modules, and still get messages about
unresolved symbols when booting

You probably reconfigured/rebuilt your kernel and excluded some
modules. You've got some old modules that you no longer use hanging
around in the /lib/modules directory. The easiest fix is to delete
your /lib/modules/x.y.z directory and do a make modules_install from
the kernel source directory again. Note that this problem only occurs
when reconfiguring your kernel without changing versions. If you see
this error when moving to a newer kernel version you've got some other
problem.

15. I installed Linux 2.1/2.3 and now I cannot load any modules!

Odd numbered Linux are development kernels. As such, it should be
expected that things break from time to time. One of the things that
has changed significantly is the way modules are handled, and where
the kernel and modules are loaded into memory.

In brief, if you want to use modules with a development kernel, you
must

* read the Documentation/Changes file and see what packages need
upgrading on your system
* use the latest modutils package, available from [59]AlphaBits on
Red Hat or the mirror site at [60]TSX-11

I recommend using at least kernel 2.1.29, if you want to use modules
with a 2.1 kernel.

16. What about dial-on-demand networking?

kerneld originally had some support for establishing dial-up network
connections on demand; trying to send packets to a network without
being connected would cause kerneld to run the /sbin/request_route
script to setup a PPP or SLIP connection.

This turned out to be a bad idea. Alan Cox of Linux networking fame
wrote on the linux-kernel mailing list

The request-route stuff is obsolete, broken and not required [...]
Its also removed from 2.1.x trees.

Instead of using the request-route script and kerneld, I highly
recommend Eric Schenk's [61]diald package to manage your demand
dialing.

Notes

[62][1]

Some distributions call this file modules.conf
[63][2]

Actually, this is not true. Late 1.3.x and all 2.x kernels support the
use of an initial ram-disk that is loaded by LILO or LOADLIN; it is
possible to load modules from this disk very early in the boot
process. How to do it is described in the
linux/Documentation/initrd.txt file that comes with the kernel
source-files.

References

1. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN26
2. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#CREDITS
3. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#INTRODUCTION
4. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#WHY
5. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#WHERE
6. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SETUP
7. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#TESTING
8. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#CONFIGURATION
9. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#BLOCKDEV
10. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#CHARDEV
11. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#ETH0
12. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#BINFMT
13. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#LDISC
14. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#NET-PF
15. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#FS
16. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SPECIAL-DEVS
17. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#MISCDEVS
18. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SCSIDEVS
19. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#PRE-POST
20. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SPYING
21. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#GOODIES
22. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#COMMONPROBLEMS
23. http://www.linuxdoc.org/
24. mailto:[email protected]
25. mailto:[email protected]
26. mailto:[email protected]
27. ftp://ftp.kernel.org/pub/linux/kernel/
28. ftp://metalab.unc.edu/pub/Linux/kernel/
29. ftp://tsx-11.mit.edu/pub/linux/sources/system/
30. http://www.linuxdoc.org/
31. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#FTN.AEN192
32. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#COMMONPROBLEMS
33. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#MISCDEVS
34. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SCSIDEVS
35. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#PRE-POST
36. mailto:[email protected]
37. ftp://sunsite.unc.edu/pub/Linux/apps/sound/mixers/
38. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN381
39. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN398
40. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN410
41. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN418
42. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN424
43. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN432
44. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN437
45. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN449
46. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN455
47. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN464
48. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN472
49. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN488
50. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN498
51. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN507
52. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN516
53. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN532
54. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#SCSIDEVS
55. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#PRE-POST
56. mailto:[email protected]
57. ftp://tsx-11.mit.edu/pub/linux/filesystems/smbfs/
58. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#FTN.AEN477
59. ftp://ftp.redhat.com/pub/alphabits/
60. ftp://tsx-11.mit.edu/pub/linux/packages/alphabits/
61. http://www.dna.lth.se/~erics/diald.html
62. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN192
63. file://localhost/export/sunsite/users/gferg/howto/00_Kerneld.html#AEN477