The Linux Kernel Hackers' Guide
Linux Kernel Hackers' Guide
Due to the fact that nearly every post to this site recently has been
either by rude cracker-wannabes asking how to break into other people's
systems or a request for basic technical support, posting to the KHG
has been disabled, probably permanently. For now, you can read old
posts, but you cannot send replies. In any case, there are now far
better resources available.
Alessandro Rubini wrote
Linux Device Drivers
, which is what the KHG could have been
(maybe) but isn't. If you have a question and can't find the answer
go get a copy
and read it--chances are that when you are done, you
will not need to ask a question here.
Run, don't walk
to get a copy of this book.
The Linux Kernel
if you want an introduction to the Linux kernel that is better
than the KHG. It is a great complement to
Linux Device Drivers
. Read it.
Table of Contents
Tour of the Linux Kernel
This is a somewhat incomplete tour of the Linux Kernel,
based on Linux 1.0.9 and the 1.1. x development
series. Most of it is still relevant.
The most common Linux kernel programming task is writing
a new device driver. The great majority of the code in the
kernel is new device drivers; between 1.2.13 and 2.0 the
size of the source code more than doubled, and most of
that was from adding device drivers.
Adding a filesystem to Linux doesn't have to involve
Linux Memory Management
A few outdated documents, and one completely new one by
David Miller on the Linux cache flush architecture.
How System Calls Work on Linux/i86
Although this was written while Linux 0.99.2 was current,
it still applies. A few filenames may need updating. find
is your friend--just respond with the changes and they will be
Other Sources of Information
The KHG is just one collection of information about the
Linux kernel. There are others!
Membership and Subscription
At the bottom of the page, you will notice two hyperlinks
(among several others):
Subscribe and Members.
Using the KHG to its fullest involves these two hyperlinks, even
though you are not required to be a member to read these pages and post
HyperNews membership is site-wide. That is, you only need to
sign up and become a member once for the entire KHG. It doesn't
take much to be a member. Each member is identified by a unique
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suggest using your email address; that way it will be unique and
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nickname if you expect to be changing your email address at any
We also want your real name, email address,
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You can change any of these items at any time by clicking on
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Subscribing to a page
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subscribe separately to each page in which you are interested
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Subscription link on the page to which
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pages that you write.
When you subscribe to a page, you subscribe to that page
and all of its responses.
Please respond to these pages if you have something to add.
Think of posting a response rather like posting to an email list,
except that an editor might occasionally come along to clean
things up and/or put them in the main documents' bodies. So if you
would post it to an email list in a similar discussion, it is
probably appropriate to post here.
In order to make reading these pages a pleasure for everyone, any
incomprehensible, unrelated, outdated, abusive, or other completely
unnecessary post may be removed by an administrator. So if you have
a message that would be inappropriate on a mailing list, it's probably
also inappropriate here.
The administrators have the final say on what's appropriate.
We don't expect this to become an issue...
About the new KHG
Linux Kernel Hackers' Guide has changed quite a
bit since its original conception four years ago. I struggled
along with the help of many other hackers to produce a document
that lived primarily on paper, and was intended to document the
kernel in much the same way that a program's user guide is
intended to document the program for users.
It was less successful than most user guides, for a number
I was working on it part time, and was otherwise busy.
The Linux kernel is a moving target.
I am not personally capable of documenting the entire
I became far too concerned with making the typesetting
pretty, getting bogged down in details and making the
document typographically noisy at the same time.
I floundered around, trying to be helpful, and made at least
one right decision: most of the people who needed to read the
old KHG needed to write device drivers, and the most
fully-developed part of the KHG was the device driver section.
There is a clear need for further development of the KHG,
and it's clear that my making it a monolithic document stood in
the way of progress. The KHG is now a series of more or less
independent web pages, with places for readers to leave
comments and corrections that can be incorporated in the
document at the maintainer's leisure--and are available to
readers before they are incorporated.
The KHG is now completely web-based. There will be no
official paper version. You need kernel source code nearby to
read the KHG anyway, and I want to shift the emphasis from
officially documenting the Linux kernel to being a learning
resource about the Linux kernel--one that may well be useful to
other people who want to document one part or another of the
Linux kernel more fully, as well as to people who just want to
hack the kernel.
Copyright (C) 1996,1997 Michael K. Johnson, email@example.com
Loading shared objects - How? by Wesley Terpstra 342.
How can I see the current kernel configuration? by Melwin
My mouse no work in X windows by alfonso santana 340.
The crash(1M) command in Linux? by Dmitry 338.
Where can I gen detailed info on VM86 by Sebastien Plante 335.
How to print floating point numbers from the kernel? by firstname.lastname@example.org 333.
PS/2 Mouse Operating in Remote Mode by Andrei Racz 331.
basic module by email@example.com 329.
How to check if the user is local? by firstname.lastname@example.org 328.
Ldt & Privileges by Ganesh 326.
skb queues by Rahul Singh 323.
Page locking (for DMA) and process termination? by Espen Skoglund 322.
SMP code by email@example.com 319.
Porting GC: Difficulties with pthreads by Talin 314.
Linux for "Besta - 88"? by Dmitry
MVME147 Linux by Edward Tulupnikov 313.
/proc/locks by Marco Morandini 310.
syscall by firstname.lastname@example.org 308.
How to run a bigger kernel ? by Kyung D. Ryu 300.
Linux Terminal Device Driver by Nils Appeldoorn
Terminal DD by Doug McNash 297.
DMA to user allocated buffer ? by Chris Read
allocator-example in A.Rubini's book by Thomas Sefzick 293.
Patching problems by Maryam
Untitled by email@example.com 290.
Ethernet Collision by jerome bonnet
Ethernet collisions by Juha Laine 289.
Segmentation in Linux by Andrew Sampson 288.
How can the kernel copy directly data from one process to another process? by Jürgen Zeller
Use the /Proc file system by firstname.lastname@example.org 286.
Remapping Memory Buffer using vmalloc/vma_nopage by Brian W. Taylor
Fixed.... strncpy to blame by Brian W. Taylor 283.
Does memory area assigned by "vmalloc()" get swapped to disk? by Saurabh Desai
Lock the pages in memory by email@example.com ->
How about assigning a fixed size array...does it get swapped too? by saurabh desai 282.
Creative Lab's DVD Encore by Brandon 274.
TCP sliding window by Olivier 273.
Packets and default route versus direct route by Steve Resnick 269.
IPv6 description - QoS Implementation - 2 IP Queues by wehrle
See the kernel IPv4 implementation documentation by Juha Laine 268.
writing to user file directly from kernel space, How can it be done? by Johan 267.
how can i increase the number of processes running? by ElmerFudd 261.
How do I change the amount of time a process is allowed before it is pre-empted? by Escher@dn101aw.cse.eng.auburn.edu 260.
Network device stops after a while by Andrew Ordin
Untitled by Andrew 259.
Does MMAP work with Redhat 4.2? by Guy
Yes, it works just fine. by Michael K. Johnson
What about mprotect? by Sengan Baring-Gould 2.
It Works! Thanks! by Guy 256.
multitasking by Dennis J Perkins
Answer by David Welch ->
multitasking by Dennis J Perkins ->
answer by David Welch 247.
linux on sparc by darrin hodges 241.
How to call a function in user space from inside the kernel ? by Ronald Tonn
How to call a user routine from kernel mode by David Welch 240.
Can I map kernel (device driver) memory into user space ? by Ronald Tonn 237.
driver x_open,x_release work, x_ioctl,x_write don't by Carl Schwartz
Depmod Unresolved symbols? by Carl Schwartz 235.
How to sleep for x jiffies? by Trent Piepho
Use add_timer/del_timer (in kernel/sched.c) by Amos Shapira 234.
Adding code to the Linux Kernel by Patrick
/dev/random by Simon Green 231.
MSG_WAITALL flag by Leonard Mosescu 230.
possible bug in ipc/msg.c by Michael Adda 225.
scheduler Question by Arne Spetzler
Untitled by Ovsov ->
thanks by arne spetzler 221.
File Descriptor Passing? by The Llamatron 220.
Linux SMP Scheduling by Angela
Finding definitions in the source by Felix Rauch 1.
Re: Linux SMP Scheduling by Franky 217.
Difference between ELF and kernel file by Thomas Prokosch 216.
How kernel communicates with outside when it's started? by Xuan Cao
Printing to the kernel log by Thomas Prokosch 213.
The way from a kernel hackers' idea to an "official" kernel? by Roger Schreiter
firstname.lastname@example.org by Michael K. Johnson 212.
Curious about sleep_on_interruptible() in ancient kernels. by Colin Howell 208.
Server crashes using 2.0.32 and SMP by Steve Resnick
Debugging server crash by Balaji Srinivasan ->
More Information by Steve Resnick ->
it should not have happenned... by Balaji Srinivasan 207.
Signals ID definitions by Franky 206.
the segment D000 is not visible by email@example.com 205.
ICMP - Supressing Messages in 2.1.82 Kernel by Brent Johnson
Change /etc/syslog.conf by Balaji Srinivasan 203.
Modem bits by Franky
Untitled by Kostya 200.
I need some way to measure the time a process spend in READY QUEUE by Leandro Gelasi 197.
How to make sockets work whilst my process is in kernel mode? by Mikhail Kourinny 193.
Realtime Problem by Uwe Gaethke
SCHED_FIFO scheduling by Balaji Srinivasan 190.
inodes by Ovsov 186.
Difference between SOCK_RAW SOCK_PACKET by Chris Leung
SOCK_PACKET by Eddie Leung 185.
Need additional termcap entries for TERM=linux by Karl Bullock 184.
Question on Umount or sys_umount by teddy 183.
Passing file descriptors to the kernel by Pradeep Gore
A way to "transform" a file descriptor into a struct file* in a user process by Lorenzo Cavallaro 181.
Dead Man Timer by Jody Winston 179.
raw sockets by lightman 178.
a kernel-hacking newbie by Bradley Lawrence
A place to start. 1.
Modems in general by Ian Carr-de Avelon 176.
How to write CD-ROM Driver ? Any Source Code ? by Madhura Upadhya 174.
Measuring the scheduler overhead by Jasleen Kaur 173.
Where can I find the tcpdump or snoop in linux? by wangc@taurus
man which by firstname.lastname@example.org 172.
Timers don't work?? by Joshua Liew
Timers Work... by Balaji Srinivasan 171.
problem of Linux's bridge code by wangc@taurus 170.
Documention on writing kernel modules by Erik Nygren 168.
How to display a clock on my console? by keco 167.
Difference between SCO and Linux drivers. by M COTE 165.
Changing the scheduler from round robin to shortest job first for kernel 2.0 and up by email@example.com
Improving the Scheduer by Lee Ingram
Improving the Scheduler : use QNX-like by Leandro Gelasi 1.
Re: Changing the sched. from round robin to shortest job first for kernel 2.0 and up. by Pirasenna V.T. 164.
meanings of file->private_data by firstname.lastname@example.org 162.
/dev/signalprocess by flatmax 161.
how to track VM page access sequence? by shawn 160.
Whats the difference between dev_tint(dev) and mark_bh(NET_BH)? by Jaspreet Singh 159.
PCI by email@example.com
RE: PCI by Armin A. Arbinger 158.
Can I make syscall from inside a kernel module? by Shawn Chang
Re: Can I make syscall from inside a kernel module? by Massoud Asgharifard
Make a syscall despite of wrong fs!! by Mikhail Kourinny 2.
code snip to make a sys_* call from a module by Pradeep Gore 1.
Dont use system calls within kernel...(esp sys_mlock) by Balaji Srinivasan 157.
Untitled by Steve Durst 154.
RAW Sockets ( Art) 153.
use phy mem by WYB 151.
HyperNews for RH Linux ? by Eigil Krogh Sorensen
Not really needed by Cameron 150.
about raw ethernet frame: how to do it ? by firstname.lastname@example.org 149.
process table by Blaz Novak 148.
Stream drivers by Nick Egorov
Streams drivers 1.
Stream in Solaris by email@example.com 143.
Xircom External Ethernet driver anywhere? by mike head 140.
interruptible_sleep_on() too slow! by Bill Blackwell
wrong functions by Michael K. Johnson 139.
creating a kernel relocatable module by Simon Kittle 138.
Up to date serial console patches by Simon Green 136.
Kernel-Level Support for Checkpointing on Linux? by Argenis R. Fernandez
Working on it. by Jan Rychter 135.
Problem creating a new system call by sauru
How did the file /arch/i386/kernel/entry.S do its job by Wang Ju 2.
system call returns "Bad Address". Why? by sauru
Re:return values by C.H.Gopinath
Re:return values by Sameer Shah 1.
possible reason for segmentation fault 1.
Creating a new sytem call: solution by C.H.Gopinath
problem with system call slot 167 by Todd Medlock 1.
Kernel Debuggers for Linux by sauru 133.
Resetting interface counters by Keith Dart 130.
writing/accessing modules by Jones MB
Use a device driver and read()/write()/ioctl() by Michael K. Johnson ->
getting to the kernel's memory by Jones MB ->
use buffers! by Rubens 124.
Help with CPU scheduler! by Lerris
Response to "Help with CPU scheduler!" by Jeremy Impson ->
Response to "Help with CPU scheduler!" (Redux) by Jeremy Impson 117.
calling interupts from linux by John J. Binder
You can't by Michael K. Johnson ->
Calling BIOS interrupts from Linux kernel by Ian Collier ->
Possible, but takes work by Michael K. Johnson ->
VBE video driver by Ian Collier ->
VM86 mode at which abstraction level? by Michael K. Johnson 116.
DVD-ROM and Linux? (sorry if it's off topic...) by Joel Hardy
DVD-ROM and linux by Yuqing_Deng@brown.edu 2.
Response to DVD and Mpeg in Linux by Mike Corrieri
DVD Encryption by Mark Treiber ->
Untitled by Tim ->
Kernel Makefile Configuration: how? by Simon Green
How to add a driver to the kernel ? by jacek Radajewski 1.
See include/linux/autoconf.h by Balaji Srinivasan 113.
Multiprocessor Linux by Davis Terrell
Building an SMP kernel by Michael K. Johnson ->
SMP and module versions by firstname.lastname@example.org 111.
Improving event timers? by email@example.com 109.
measuring time to load a virtual mem page from disk by kandr 94.
using cli/sti() and save_flags/restore_flags() by george 93.
Protected Mode by ac
'Developers manual' from Intel(download)... by Mats Odman 1.
Advanced 80386 Programming Techniques by Michael K. Johnson 92.
DMA buffer sizes by firstname.lastname@example.org
DMA limits by Albert Cahalan <acahalan at cs.uml.edu> 1.
Not page size, page order by Michael K. Johnson 91.
Problem Getting the Kernel small enough by email@example.com
Check it's the right file, zImage not vmlinux by Cameron 1.
Usually easy, but.... by Ian Carr-de Avelon 89.
How to create /proc/sys variables? by Orlando Cantieni 88.
Linux for NeXT black? by Dale Amon 87.
vremap() in kernel modules? by Liam Wickins 86.
giveing compatiblity to win95 for ext2 partitions (for programmers forced to deal with both) by pharos
Well, What's the status of the Windows / Dos driver for Ext2? by Brock Lynn 1.
Working on it! by ibaird
revision by ibarid ->
Untitled by Olaf 84.
setsockopt() error when triying to use ipfwadm for masquerading by firstname.lastname@example.org
Re: masquerading by Charles Barrasso 83.
reset the irq 0 timer after APM suspend by Dong Chen
Re: fixed, patch for kernel 2.0.30 by Dong Chen 77.
Source Code in C for make Linux partitions. by Limbert Sanabria
Untitled by lolley 76.
How can I "cheat" and change the IP address (src,dest) in the sent socket? by Rami
Transparent Proxy by Zygo Blaxell 4.
Untitled by email@example.com 3.
Untitled by firstname.lastname@example.org
Changing your IP address is easy, but... by Zygo Blaxell 1.
You have to know a bit of C (if u wanna learn) ;) by Lorenzo Cavallaro 2.
Do it in the kernel by Michael K. Johnson 74.
Where is the source file for accept() by email@example.com
Here, in /usr/src/linux/net/socket.c by firstname.lastname@example.org 72.
How can I use RAW SOCKETS in UNIX? by Rami
Re: Raw sockets by email@example.com 69.
the KHG in spanish? by Jorge Alvarado Revatta
Si tenga preguntas, quisa yo pueda ayudarte. by KernelJock
Tengo una pregunta by firstname.lastname@example.org 2.
Español by LL2 1.
No esta aqui! Pero... by Michael K. Johnson 67.
How to get a Memory snapshot ? by Manuel Porras Brand
Why not to get a memory snapshot? by Jukka Santala ->
Why you would want to get a memory snapshot by Dave M. 66.
resources hard limits by email@example.com
Setting resource limits by Jukka Santala 65.
How to invalidate a chache page by Gerhard Uttenthaler
Read the rest of the KHG! by Michael K. Johnson 64.
Where are the tunable parameters of the kernel? by firstname.lastname@example.org
Kernel tunable parameters by Jukka Santala 62.
How can my device driver access data structures in user space? by Stephan Theil
Forced Cast data type by Wang Ju 61.
Problem in doing RAW SOCKET Programming by anjali sharma
Problem with ICMP echo-request/reply by Raghavendra Bhat 59.
Tunable Kernel Parameters? by email@example.com
Increasing number of files in system by Simon Cooper
Increasing number of open files parameter by Simon Cooper 1.
sysctl in Linux by Jukka Santala
Setting and getting kernel vars by firstname.lastname@example.org 58.
ELF matters by Carlos Munoz
Information about ELF Internals by Pat Ekman 57.
Droping Packets by Charles Barrasso
[Selectively] Droping Packets by Jose R. cordones 56.
The /proc/profile by Charles Barrasso
readprofile systool by Jukka Santala 55.
Can you block or ignore ICMP packets? by HackOps@nutnet.com
ICMP send rate limit / ignoring by Jukka Santala
Omission in earlier rate-limit... by Jukka Santala ->
Patch worked... by Jukka Santala 3.
Using ipfwadm by Charles Barrasso
ipfwadm configuration utility by Sonny Parlin 1.
Icmp.c and kernal ping replies by Don Thomas 52.
encaps documentation by Kuang-chun Cheng 51.
Mounting Caldrea OpenDOS formatted fs's by Trey Childs 49.
finding the address that caused a SIGSEGV. by Ben Shelef 47.
sti() called too late. by Erik Thiele
sti() called too late. by Gadi Oxman 38.
Module Development Info? by Mark S. Mathews
Needed here too by ajay 2.
Help needed here too! by ajay 35.
Need quicker timer than 100 ms in kernel-module by Erik Thiele
10 ms timer patch by Reinhold J. Gerharz
please send me 10 ms timer patch by Tolga Ayav 1.
Please send me the patch by Jin Hwang
UTIME: Microsecond Resolution Timers by BalajiSrinivasan 34.
Need help with finding the linked list of unacked sk_buffs in TCP by Vijay Gupta 31.
Partition Type by Suman Ball 30.
New document on exception handling by Michael K. Johnson 29.
How to make paralelism in to the kernel? by Delian Dlechev 27.
readv/writev & other sock funcs by Dave Wreski 25.
I'd like to see the scheduler chapter by Tim Bird
Untitled by Vijay Gupta 3.
Go ahead! by Michael K. Johnson 21.
Unable to access KHG, port 8080 giving problem. by Srihari Nelakuditi
Get a proxy by Michael K. Johnson 20.
proc fs docs? by David Woodruff
Examples code as documentation by Jeremy Impson 18.
What is SOCK_RAW and how do I use it? by arkane
What raw sockets are for. by Cameron MacKinnon 15.
Linux kernel debugging by email@example.com
GDB for Linux by David Grothe
Another kernel debugging tool by David Hinds
Kernel debugging with breakpoints by Keith Owens ->
Need help for debugging by C.H.Gopinath 1.
gdb debugging of kernel now available by David Grothe 1.
Device debugging by alombard©iiic.ethz.ch 9.
Realtime mods anyone? by bill duncan
Summary of Linux Real-Time Status by Markus Kuhn 6.
Hard real-time now available by Michael K. Johnson
Shortcomings of RT-Linux by Balaji Srinivasan 1.
Firm Realtime available by Balaji Srinivasan 5.
found some hacks ?!? by Mayk Langer
I want to know how to hack Red Hat Linux Release 5.0 by Kevin 4.
POSIX.4 scheduler by Peter Monta
cli()/sti() latency, hard numbers by Ingo Molnar 2.
Realtime is already done(!) by Kai Harrekilde-Petersen 1.
100 ms real time should be easy by jeff millar
Real-Time Applications with Linux POSIX.4 Scheduling by P. Woolley 7.
Why can't we incorporate new changes in linux kernel in KHG ? by Praveen Kumar Dwivedi
You can! by Michael K. Johnson 3.
Kernel source code by Gabor J.Toth
The sounds of silence... by Gabor J.Toth
Breaking the silence :) by Kyle Ferrio
Scribbling in the margins by Michael K. Johnson 2.
It requires thought... by Michael K. Johnson 2.
Kernel source is already browsable online by Axel Boldt 2.
Need easy way to download whole KHG
KHG being mirrored nightly for download! by Michael K. Johnson 2.
postscript version of these documents? by Michael Stiller
Sure! by Michael K. Johnson ->
Not so Sure! by jeff millar ->
Enough already! by Michael K. Johnson 1.
Mirror packages are available, but that's not really enough by Michael K. Johnson
Mirror whole KHG package, off line reading and Post to this site by Kim In-Sung
Untitled by Jim Van Zandt 1.
That works. (using it now). Two tips: by Richard Braakman
Appears to be a bug in getwww, though... by Michael K. Johnson ->
Sucking up to the wrong site... ;) by Jukka Santala 1.
Help make the new KHG a success by Michael K. Johnson