[FAQ] Kernel Mailing List FAQ and Policy V1.11

10 Apr 1997 12:29:51 +0200

Kernel Mailing List FAQ and Policy V1.11

This is the first official release of the Linux Kernel Mailing List
FAQ and Policy. From now on it will be posted to the list on the first
day of every month.

It also is accessable on <URL:http://www.iconsult.com>

Please comment on the current changes; your input will make this draft
reflect the wishes of the list members exactly. Lots of thanks to the
people that already did, your comments were invaluable for creation of
this document.

If you find spelling errors or bad grammar, please mail corrections to
kernelfaq@iconsult.com, and they will be included in the next version
of the draft.

$Revision: 1.11 $ (See Appendix C for a change log.)

= 0. = Introduction
= 1. = The kernel mailing list
= 1.1. = How do I get off of this mailing list ???
= 1.2. = Topic
= 1.3. = Off-topic
= 1.4. = Etiquette
= 1.5. = Bug Reports
= 1.6. = Kernel patches
= 1.7. = Be ready to get spammed
= 2. = On- and off-line resources
= 2.1. = Kernel resources
= 2.1.1. = The Linux Kernel HOWTO - How to compile a kernel
= 2.1.2. = Linux v2 Information HQ
= 2.1.3. = The kernel hackers guide
= 2.1.4 = Mailing lists
= 2.1.5. = Writing device drivers
= 2.1.6. = The Linux Wish List
= 2.1.7. = Periodicals
= 2.1.8. = Books
= 2.2. = Other points of interest
= 2.2.1. = The Linux Home Page
= 2.2.2. = The Linux documentation project
= 2.2.3. = The Linux Software Map
= 2.2.4. = IRC
= 2.2.5. = Linux news groups
= 2.2.6. = Linux Gazette
= 2.2.7. = Other URLs
= 3. = The kernel
= 3.1. = Common problems
= 3.1.1. = Before you dive into it
= 3.1.2. = File system corruption
= 3.1.3. = Signal 11
= 3.1.4. = Seasonal Problems
= = Warning: possible SYN flooding. Sending cookies.
= = Kernel hangs / no output after "Now booting the kernel ..."
= = Ignoring P6 Local APIC Spurious Interrupt Bug
= 3.2. = How to get started on kernel development
= A. = Appendix A - Maintainers
= B. = Appendix B - Linux Kernel Mailing List Bug Report Form
= C. = Appendix C - Unresolved Issues
= D. = Appendix D - Change Log

= 0. = Introduction

This is the Linux kernel mailing list FAQ and usage policy. It is
posted to the mailing list regularly. On the World Wide Web it is
available on <URL:http://kernelfaq.iconsult.com>.

Note that thisq FAQ is not so much a FAQ but more a collection of
"frequent answers".

The first section contains information about the kernel mailing
list. Please read it before posting to the list or be ready to be

= 1. = The kernel mailing list

= 1.1. = How do I get off of this mailing list ???

Send mail containing "unsubscribe linux-kernel" (without the quote
marks) in the body of the message (not the subject line) to

(echo "unsubscribe linux-kernel" | mail majordomo@vger.rutgers.edu)

If that doesn't work you probably are subscribed using another
email address than the one you're using now. In that case the
first thing to do is to find out the email address you subscribed
with. (You're on your own here, but your system adminstrator
might help you by checking the mail transfer agent's log files)

When you found out the address use:

(echo "unsubscribe linux-kernel" "the address you subscribed with"
| mail majordomo@vger.rutgers.edu)

By the way, a small tip for mailing lists in general: On some
mailing lists the "unsubscribe <list> <address>" syntax doesn't
work. In that case use Netscape Navigator to send a mail with
faked sender address: Enter your "address you subscribed with" in
Netscape's "Options/Mail and News preferences/Your Email" field,
fill in your current address in the "Reply-to Address" and send
the unsubscribe mail from Netscape. Normally the mailing list
software will believe the faked "From:" field in the mail.

= 1.2. = Topic

This list discusses Linux kernel development. All submissions
relevant to that, such as bug reports, enhancement ideas, kernel
patches or reports that a patch fixed a bug are appropriate.
Please note the emphasis on kernel development as opposed to
development of Linux systems in general.

= 1.3. = Off-topic

Please do not ask basic installation or non-kernel related
configuration questions on this list. If you are unclear of the
distinction between the Linux kernel and other parts of a Linux
system, please do not post here until you have learned somewhere
else. In particular, if you don't know the difference between
XFree86 and the Linux kernel, please do not ask about it here.
(If you don't know what I'm talking about, this means you.)

= 1.4. = Etiquette

As Linux grows in popularity, it is inevitable that subscriptions
to the list will greatly increase. The list is already quite
large and beginning to suffer from the classic Usenet signal to
noise ratio problem. Reading the list daily gives a sense of
involvment and excitement at being so close to the cutting edge of
a compelling and rapidly evolving technology. It is important to
note that your post will go out to many, many people and that
"send" key is so very close... A good idea to consider: "My
opinions really don't matter, but my _code_ most certainly does!"
Please help us to prove that this list can scale well to such a
large audience.

- Questions

Before posting a question to this list, think twice about
whether it is indeed kernel-related. Perhaps another newsgroup
or mailing list is better suited for the question. See Section
2 for a list of on-line resources.

In any event have a quick look at the Documentation/Changes
file, and ensure that your software is up-to-date. Sometimes
things change within the kernel which stop user-level code from
working. You'll feel a little silly if the answer to the
problem is in the documentation that comes with the kernel, but
you just didn't read it.

A good strategy is to wait a day after writing something before
posting. The very same information may hit the list during that
time, especially if the problem you are experiencing is one
which many people will find (e.g., "ps and top have stopped
working!"). Probably someone else will ask about it too;
there's nothing more annoying than seeing the same question on
the list over and over again.

- Answers

Before posting an answer to this list, also think twice! When
off-topic mail arrives (e.g., "I can't build the kernel", "how
do I convert ASCII to EBCDIC" or "Make money fast"), it is best
to answer directly (i.e., off this list). Despite our best
efforts, these questions will always appear; there is no easy
way to avoid this without moving away from creative anarchy.
Dumb questions are at least a positive sign of usage and growth.
We all hate spam, but flaming to the list just makes it worse.

Before you post an answer to a legitimate question, think twice
again. If possible try to give an answer that might help more
people than the original poster. For example posting generic
strategies helps a lot of people (especially newbies). Some
great examples of such posts by Cameron McKinnon (how to get
started) and Doug Ledford (on extfs problems) have ended up in
this document.

I know all those 'think twice' are more easily said than done, but
remember _everyone_ that even tries to think will make the kernel
mailing list a more enjoyable place for all.

"Most people think about twice a year. I got famous by thinking
once a week." - George B. Shaw (see Appendix A)

= 1.5. = Bug Reports

There are a few things to consider before reporting kernel error

- Try to have a clue

A good rule of thumb that applies to everything in life - even
to linux kernel development. Think of things that might be of
interest to the developers, things that are redundant. Find out
how other people's report bugs look and what the reaction in the
list is.

- The developers don't have access to your system.

This means they don't have much information on how your kernel
was built, which addresses certain routines were compiled to or
which hardware you run. To get a rough idea what information
might be relevant to the developers read the following
paragraphs, then have a look at the bug report form and data
collection shell script in Appendix B.

The most complicated thing to do is to add symbolic information
to your kernel error message. Once (back in the good old days)
this was quite an ordeal, but with modern klogd/syslogd install
this gets quite easy. Make sure your kernel's System.map is
installed in the right place (/boot/System.map, /System.map or
/usr/src/linux/System.map) and from now on klogd will
automatically add symbolic information to the kernel messages it
logs. See 'man klogd' to check whether the version of klogd you
run does already support that feature.

For similar functionality look at the ksymoops program in the
kernel source tree, which can be used when klogd/syslogd logged
a 'raw' kernel Oops.. message to your disk (or if you copied it
down by hand, because the system froze before being able to
write to the hard disk.)

When symbolic information is added to the report you'll have to
provide everything else relevant to the problem. A general rule
of thumb is: Too much information won't hurt, not enough will.
Be sure to include at least some general description of your
hardware like processor, RAM, how many and what kind of disks,
disk controllers (IDE? SCSI?) and expansion board. In
particular, make sure you mention which kernel you are trying to
use. Use the bug report form and data collection shell script
from Appendix B.

If you feel you should include your .config file, please send
the output of "grep '^[^#]' .config" instead of the whole thing,
as this saves a lot of wasted space.

- The developers are busy developing

Often the developers are so busy developing, they will read your
mail but not have the time to answer it. While you might say
'it does not take much time to answer an email' you might
overlook the fact that developers often get flooded with email,
so much that they get nightmares about it. Answering an email
does in fact not take much time, answering 100 emails does.

- Trying to help the developers makes the bug vanish faster ...

If you like to be of great help to the developers you might find
out if other people have the same problem. Finding the general
patterns of a bug is a job that does not take months, and it is
a job that you can perform if you have never seen a single line
of C source.

Try to find some conditions that reliably trigger the problem,
this includes asking other people if they have similar problems.
If yes, which hard- and software do they use? For example you
might find out your ext2fs file system errors are limited to
users of the brand xyz SCSI controller Mark 42. _Such_ a result
will alert the developer of the xyz SCSI driver, while a message
like 'My ext2fs got bad! Linux sucks!' probably won't.

- Try to reach the appropriate people.

Sometimes it is better to communicate to the developers directly
by email instead of posting to the mailing list. See the
MAINTAINERS file in the Linux source tree to find out the
maintainer for a specific Linux subsystem. In addition, there
are a number of mailing lists for specific parts of the kernel
(e.g. scsi, net, etc.); you might want to join those lists as
well, since that is where the experts hang out.

- Use the Linux kernel mailing list bug report form from Appendix
B of this document. This form will ask the right questions.

= 1.6. = Kernel patches

A little bit of consideration first: If possible create patches
that change _one_ thing in the kernel. Doing so enables people to
choose which part of your changes they use (or even include in the
distribution kernel.) While your SCSI driver fixes might be
perfectly sane, people might not like your change to the network
layers changing network addresses from being big-endian to

Always use unified (-u) diff format when submitting kernel
patches. The unified diff format is very readable and allows
'reverse' application for undoing a patch (which is extremely
useful when the patch provider 'diffed' the sources the wrong way

Assuming you have two source trees of the _same_ version of Linux,
an original one {original-source-tree} and one with your personal
changes {your-source-tree}, the recommended procedure for creating
patch files is:

$ make -C {original-source-tree} distclean
$ make -C {your-source-tree} distclean
$ diff -urN {original-source-tree} {your-source-tree} >/tmp/linux-patch

The patch file will then be in /tmp/linux-patch waiting to be
deployed on the Linux kernel mailing list. When posting your
patch, don't forget to mention what it does.

Of course you need to set up two identical source directories to
be able to diff the tree later. A nice trick -- it requires a
little bit of consideration, though -- is to create the
'your-source-tree' from hard links to the 'original-source-tree':

$ tar xzvf linux-2.1.anything.tar.gz
$ mv linux linux-2.1.anything.orig
$ cp -av --link linux-2.1.anything.orig linux-2.1.anything

This will hardlink every source file from the original tree to a
new location; it is very fast, since it does not need to create
more than 20 megabytes of files.

You can now apply patches to the linux-2.1.anything source tree,
since patch does not change the original files but move them to
<filename>.orig, so the contents of the hard-linked file will not
be changed.

Assuming that your editor does the same thing, too (moving
original files to backup files before writing out changed ones)
you can freely edit within the hardlinked tree.

Now the changed tree can be diffed at high speed, since most files
don't just have indentical contents, they are identical files in
both trees. Naturally removing that tree is quite fast, too.

Thanks to Janos Farkas <URL:mailto:chexum@shadow.banki.hu> for
that trick.

= 1.7. = Be ready to get spammed

Some "nice guys" are obviously monitoring the kernel mailing list
to get email addresses. Every time I post to the mailing list I
get a bunch of "Earn $800 a week extra income" mails. Be ready to
ignore or handle this (maybe using procmail).

= 2. = On- and off-line resources

If you think something should be listed here, please send an e-mail
to the current list maintainer (<URL:mailto:kernelfaq@iconsult.com>).
Resources will be listed in "URL embedded in text file" syntax to
ease transition to these resources.

= 2.1. = Kernel resources

= 2.1.1. = The Linux Kernel HOWTO - How to compile a kernel

You definitley ought to look at this unless you can cite every
line of the kernel Makefile from memory.

This document describes how to obtain, unpack, compile and install
a new kernel and shows some of the pitfalls that lurk on the road
of upgrading.


If you are looking for all the other HOWTOS and mini-HOWTOS just
check out LDP itself:


= 2.1.2. = Linux v2 Information HQ


A very useful site that lists Linux V2 information including, but
not limited to, "what's new", "how to upgrade", source code,
official and unofficial kernel patches for V2.0 and V2.1 and
archives of the Linux mailing lists. Two thumbs up.

Please note that this was known as <URL:http://www.ecsnet.com> for
some time, and while the latter URL will continue to be vaild for
a while, it will eventually go away; it might be wise to update
bookmarks to reflect the new location.

= 2.1.3. = The kernel hackers guide


Once upon a time it was a paper document but due to the 'moving
target' nature of a constantly developed kernel it is now
completely web-based, using a hyper-news system so users can
add input.

= 2.1.4 = Mailing lists

As mentioned above, there are a number of more specialised Linux
mailing lists. Many of these are run from vger.rutgers.edu. To
get a listing of those running at vger, send an e-mail to
<URL:mailto:majordomo@vger.rutgers.edu>, containing the single
word "lists". Some of the lists are mentioned in the MAINTAINERS
file in the Linux source code.

A lot of mailing lists are archived at the Linux v2 Information HQ

Having a close look at the linux-admin list would be
worthwile. Many of the off-topic questions on linux-kernel are
appropriate for linux-admin and the latter list seems to be pretty
well behaved. The admin list is approaching the amount of traffic
on the kernel list.

= 2.1.5. = Writing device drivers


A paper of a talk by Michael K. Johnson given at Spring DECUS'95.
According to the author this is probably a bit dated but might be
still worth reading.

= 2.1.6. = The Linux Wish List


The Linux Wish List, compiled from the contents of the kernel
mailing list. Check this before posting enhancement requests to
the mailing list or to get some inspiration for your kernel

= 2.1.7. = Periodicals

- Linux Journal


Linux Journal has had a long-running series of articles called
Kernel Korner which, has had quite a bit useful information in
it. Four articles on writing runtime-loadable character device
drivers in issues 23 - 26 have been made available on Linux
Journal's WWW Site:


= 2.1.8. = Books

There aren't any book reviews in this section, just pointers to
those. First you might want to look at Cameron McKinnon's article
on geting started with kernel development, which also mentions
some books.

The next place to stop is the Linux Reading List Mini-HOWTO, which
although being a bit dated list a lot of the books useful to
kernel programmers:


= 2.2. = Other points of interest

= 2.2.1. = The Linux Home Page


A very good starting point for the new and old Linux user. It
contains many starting points including information on the history
and creation of Linux, FAQ's and HOWTO's, Linux Software Map,
Manual Pages, Usenet Newsgroups, Where To Get Linux, Linux
Documentation Map, Linux International, Linux On The World Wide
Web, Hot Linux News, Linux Gazette, and Linux Journal.

= 2.2.2. = The Linux documentation project

The Linux documentation project:


The LDP contains _loads_ of Linux documentation, including, but
not limited to the HOWTOS, FAQs, manpages and various guides.

= 2.2.3. = The Linux Software Map

There are a few different web frontends for the Linux Software Map:


If you prefer downloading the whole database and browsing it
offline get it at:


= 2.2.4. = IRC

There is said to be online support on IRC, namely servers
irc.linpeople.org ( or vinge.linpeople.org. Look for
the channels #help or #natter.

Also irc.blackdown.org is a good place for advanced topics and
kernel hackers.

An IRC client is required to connect to the many IRC networks
available on the Internet. A goot place to find IRC clients is:


= 2.2.5. = Linux news groups

Benefits of Linux compared to other operating systems

Announcements important to the Linux community. (Moderated)

FAQs, HOWTOs, READMEs, etc. about Linux. (Moderated)

Writing Linux applications, porting to Linux

Linux kernels, device drivers, modules

Hardware compatibility with the Linux operating system

Linux operating system on 680x0 Amiga, Atari, VME

Linux-specific topics not covered by other groups

Networking and communications under Linux

Linux installation and system administration

Linux X Window System servers, clients, libs and fonts

= 2.2.6. = Linux Gazette


The Linux Gazette is a monthly compilation of basic tips, tricks,
suggestions, ideas, and short articles about Linux designed to
make using Linux fun and easy. LG began as a personal project of
John M. Fisk, and grew to include contributions freely provided by
a growing number of authors.

= 2.2.7. = Other URLs

- Linux kernel

- Linux on the web

- Sunsite Linux archive

- Find new files on Sunsite

- Linux kernel change summary

- Linux Source Navigator

- Linux archive search

- Linux network drivers

- Linux SMP project

- Linux NOW!

- Linux applications and utilities page

- Woven goods for linux - a collection of WWW applications and
hypertext-based information about Linux.

= 3. = The kernel

= 3.1. = Common problems

= 3.1.1. = Before you dive into it

Read up on all strategies for error recovery. Your file system
corruption might be caused by the same problem that causes another
user's Signal 11 trouble; a kernel is a complex piece of software,
and errors happening in the kernel or in hardware below might
cause every thinkable and unthinkable kind of problem. Errors
propagate in unforseeable ways. There are hardware problems which
show up only on Linux while Win95, NT, OS/2, Doom and Quake run
fine on the same computer. You are dealing with software handling
hardware, this is extremely complex and right next to black magic.
Flipping one bit of memory in the kernel creates strange results,
just like adding a drop of tabasco sauce to a witch's cauldron
might make her conjure up a horde of croaking frogs instead of the
(by her) desired white prince.

= 3.1.2. = File system corruption

"On a block device (block size 1024 bytes) with ext2fs, I don't
reliably get back from a file what I first wrote in."

Normally any kind of file system corruption is a sign of hardware
problems or problems with a low level I/O driver. Ext2fs is a
quite tested and stable file system, but due to its high
performance it is likely to dig out problems in the lower levels
of the system.

When I experienced ext2fs file system corruption myself, a query
on the linux newsgroups showed others had experienced similar
problems. It turned out to be a firmware problem in the Conner
CFP1060S hard drive, when data was read _really fast_ the buffer
cache algorithm in the drive firmware failed.

There are a lot of things to try when you get ext2fs corruption:

- Use tune2fs to set your file system to drop into read only mode
when an error occurs. This will prevent small errors causing
catastrophes. The command is:

tune2fs -e remount-ro /dev/???

You should also use that command to set a time interval between
file systems checks, because (especially on long running
servers) it can take eons to reach the maximum mount count.

- Check the partition tables

Especially on the Intel x86 platform partition tables can easily
be broken. Such a problem can occur when the drives were
partitioned using another disk controller than they are used
with. Use fdisk dump the tables and ensure partitions are set
up correctly.

- Tune Linux and your BIOS to slow and safe parameters. Turn off
bus (PCI) optimizations.

- Use an empty partition to check if the problem lurks in the
kernel levels below the file system. Probably the most simple
test is to copy /dev/zero to the partition (using dd) and
comparing the partition and /dev/zero afterwards (using cmp) if
there are any differences.

A very thorough test has been suggested on the mailing list by
Doug Ledford <URL:mailto:dledfor@dialnet.net>:

"I'll go one step further with this. I would recommend that
the people having problems with ext2fs corruption run the
following test (if possible):

Let's say you have a hard drive partition of decent size that
you don't mind losing the data on (or even if you do mind,
this test can turn up a lot of errors so if you have an
inconvenient way of getting back, then you should probably do
this anyway)

First, get the exact size of the partition (or the whole drive
as the case may be in some circumstances) in 1K blocks.

Divide this total number of blocks into 4 equal chunks (most
drives do this easily, some may have a few odd sized chunks).

Write a script like this:

badblocks -w -s -b 1024 -o /tmp/list.1 /dev/??? (blocks * .25) 0 &
badblocks -w -s -b 1024 -o /tmp/list.2 /dev/??? (blocks * .5) (blocks * .25) &
badblocks -w -s -b 1024 -o /tmp/list.3 /dev/??? (blocks * .75) (blocks * .5) &
badblocks -w -s -b 1024 -o /tmp/list.4 /dev/??? (blocks) (blocks * .75) &

A simple shell script like this will run four simultaneous
badblocks programs on the drive. A person can then check the
files in the /tmp directory to see if any were returned as
bad. With modern IDE or SCSI drives, all of these files
should have a zero length unless one of two things is true.
One, you have a drive developing too many bad sectors to be
mapped out (which is cause for alarm in itself) or two, you
have corruption in your low level driver (or other low level
hardware such as memory or cache or bus transfer problems).
If these test return all 0 length files, then we should start
looking elsewhere for the problem. Run the test several
times, as a single pass may not show the problem. If you are
really courageous, you can try doubling the tests by splitting
the drive into 8 equal chunks (or if you have two drives you
can do both drives at four chunks each at the same time).
This is a standard test I use with the aic7xxx driver to find
problems with tagged queueing and high commands per lun
values. It seems to show problems much quicker than any
file system activity would (in my case, I had as many as 24 of
these running simultaneously on 6 drives in order to test this
out, talk about a dog slow machine, it took about 5 minutes
just to start X windows under this load).

In any case, running tests like these to rule out hardware
corruption would help greatly in increasing the level of
confidence that somehow the ext2fs layer is at fault (which I
personally don't think it is except under very rare occasions
since I have a hard hit news server running that file system
without problems, but I've taken the care and gone to the
lengths to run these tests on the particular hardware in that
machine and identified bad combinations that can cause
problems and worked around them at the driver level)."

Later on Doug followed up to another article on the ext2fs
corruption thread:

"Correct. And it's very useful information to have at that.
If you can produce corruption problems without going through
the ext2fs code, then you have hardware corruption of some
sort. An example of some of the things in the past that I
have personally seen cause hardware corruption which made one
*THINK* that something was wrong with the ext2fs code when
there wasn't:

1. Bad CPU fans on pentium and high speed 486 machines
2. Bad SCSI cables
3. Memory timing settings in BIOS being just a tad too
4. Bad memory
5. Bad Pipeline Burst (or other) cache
6. Too long of a SCSI or IDE cable
7. Interference between SCSI and IDE cables running in
close proximity to each other
8. Flaky CPU (had been overclocked and partially burnt out)
9. Esoteric BIOS options being enabled when they shouldn't be
(this takes some experimentation to find and fix, a change
BIOS settings, test to see if problem is gone, if not, reboot
and change settings again type thing)

These are a few examples. A second thing to keep in mind is
that the ext2fs is a rather fast filesystem by unix standards
(it beats the hell out of the EAFS HTFS DTFS etc filesystems
from SCO, but who's comparing SCO to linux anyway :) so if you
have hardware corruption problems that don't show up except
under heavy load, ext2fs is a good filesystem to bring those
out :)

And of course, the very reason I posted my original email as
part of this thread. A person needs to always keep in mind
that if they are getting ext2fs errors about corruption, this
does *NOT* always mean the ext2fs is at fault. It means that
somewhere along the way, either due to code in the ext2fs, or
code in the block driver you are using, or code in the low
level driver you are using, or somewhere between the CPU, RAM,
cache, bus, controller, drive bus, drive, and magnetic media,
something is getting corrupted. It is important in these
cases to try and isolate software faults from hardware faults.
The purpose of the "script" I posted was to give a convenient
way of trying to narrow down the line between hardware and
software. There is still software involved with that script,
but not as much. You are down to just the badblocks program,
the various buffer mechanisms, and the block driver itself
(with its underlying low level driver). Generally speaking,
the buffer cache is considered to be safe code, so you can
rule that out. Most of the block drivers are considered to be
the same, so they can be ruled out. This leaves the
underlying low level driver and the badblocks program as
suspect. The badblocks program is rather simple in design,
and an inspection of the source will result in the conclusion
that it too can be ruled out (not to mention how many times
it's been used to find these problems, yet I've never once
heard of it causing sectors that are fine to be mapped as bad
unless the underlying driver had problems). That means that
the script I posted is really stressing hardware and your
underlying low level driver. All in all, that greatly reduces
the number of variables to look at. So, a failure during the
testing by the badblocks program gives a person somewhere to
look. They can either fiddle with compile options for their
low level driver, or they can start the process of trying to
enable/disable things in the computer's BIOS to try and find a
culprit (disable cache this run, delay memory timings that
run, etc) which then allows a person to try and pinpoint the
exact problem, get it fixed, and be on their way :) Further,
as long as you fail this test, there is no sense at all in
even looking at the ext2fs code since you won't know if you've
fixed anything by changing it unless something you did just
happened to slow things down enough to keep the problem from
showing up. In this case, instead of slowing the machine down
to be reliable and leaving fast code in place, you've slowed
the code down so it doesn't break your faulty hardware."

- Use debugging tools to check your system.

Memtest-86, a thorough, stand alone memory tet for 386, 486 and
586 systems:


If you think a particular tool shall be listed please mail to

= 3.1.3. = Signal 11

If your processes frequently die because of a signal 11, there
might be a problem with your hard- or software. There's a FAQ
regarding signal 11 at <URL:http://www.bitwizard.nl/sig11>.

You should read the Signal 11 FAQ even if you have a different
problem; the procedures mentioned in the FAQ will probably help
finding that one, too.

= 3.1.4. = Seasonal Problems

= = Warning: possible SYN flooding. Sending cookies.

> I got 44 of these 2 days ago, then another 35 more.
> " Warning: possible SYN flooding. Sending cookies."

This need not be an attack. It _does_ mean that your backlog has
become full. This can be a consequence of crummy network
connections between you and legitimate remote sites. If you
normally don't see 67 connection attempts per second then it's
probably an attack.

> My interpretation is that somebody has flooded the irc port to
> kill the server, am I right? What are the chances that this is
> not an attack, but just "one of those things?"

It very much depends on how busy your irc port is and how bad
network conditions are between you and the users of your irc. To
really find out if you are being attacked you would need to start
taking TCP dumps and look for streams of SYN packets with
addresses that are unreachable. Large numbers of packets from the
same unreachable address would be a give away.

Answered by Eric Schenk <url:mailto:Eric.Schenk@dna.lth.sh>

= = Kernel hangs / no output after "Now booting the kernel ..."

> The kernel is loaded, uncompressed and it hangs after the
message "Now booting the kernel...".

Are you sure you have VTs enabled? They became optional in
2.1.31, and default to being disabled.

= = Ignoring P6 Local APIC Spurious Interrupt Bug

> Is there a problem with the P6? Or with the board? If it's a
> problem with the P6, do all P6's have this problem? Does this
> bug affect the system in any way?

It's a problem with the Local APIC on most steppings of the
Pentium Pro CPU. Specifically, a spurious interrupt is delivered
as an exception 15 (a reserved code) rather than as interrupt 15.
The bug is benign, so long as the kernel ignores the exception 15.

> Is it a problem to comment out the line in the kernel that shows
> this message? It's messing up the display.

You can safely comment it out.

Answered by Leonard N. Zubkoff <url:mailto:lnz@dandelion.com>

= 3.2. = How to get started on kernel development

Cameron MacKinnon <URL:mailto:mackin@interlog.com> wrote a wonderful
article on that topic:

"... I'm not a pro, but I generally know what's going on for
least part of the time. Here's what I did:

I bought books. Here's reviews: LINUX Kernel Internals, Beck et
al, Addison Wesley, 0-201-87741-4. I read about a third of
it. It's dated (1.2 kernels) and doesn't have anything about
SCSI in it, but it's the only Linux kernel book out
there. There's a new version out for 2.0 kernels, but only in
the original German. 'The Design and Implementation of the 4.4
BSD Operating System', McKusick et al, Addison Wesley,
0-201-54979-4. A much more readable book, IMHO. It talks about
the BSD design in general, why things changed over time, why and
how specific performance tradeoffs were made, etcetera. Also,
'The Magic Garden Explained' or something like that, borrowed,
pub. and ISBN unknown. This book is a very thorough coverage of
the design of System 5 Release 4 (SVR4), but not as easy to read
as the BSD book. Bottom line: Beg, borrow, check out or steal
one book, any book, on the design of the UNIX operating
system. Sit in a library or a bookstore reading it, if you
haven't got the money. You need to understand how schedulers,
pagers, swappers, top and bottom halves, wait queues, inodes,
ttys, the boot process, init and some other stuff work. Most of
this stuff will be applicable to Linux at the concept level,
regardless of the book (ignore anything on SysV STREAMS). Unless
you're extremely gifted, the concepts won't reveal themselves to
you from kernel source code. LEARN THE CONCEPTS. The Linux
community is not a good place to do this - this list assumes
that if you're here, you already know them. If you're one of
those truly unlucky people with no access to such a book, try to
find this info on the net. I've never really looked. If all else
fails, proceed to step two:

I read Michael Johnson's Kernel Hackers' Guide. It wasn't
perfect when I read it, but that was a while ago. 1) It's
probably perfect by now. 2) It's free. You can get it anywhere,
including here: <URL:http://www.redhat.com:8080/HyperNews/get/khg.html>
It does a good job of mapping the concepts you just learned to
actual kernel function calls and processes in Linux. Also, many
kernel functions have man pages, though they're horribly out of

I subscribed to mailing lists. Initially I was all over: gcc,
kernel, a few scsi lists, security... Now I've got it down to a
core of kernel, two SCSI driver lists, DIALD, security and
SMP. Don't be afraid to subscribe to a lot of lists (read-only!)
for a few weeks to see what interests you. You can always
unsubscribe later. Some people prefer reading the lists via
news, but I'd recommend mail: You SAVE the mail on your hard
disk. It becomes your personal reference library (N.B. UNIX has
some really great text search and processing tools). You read
all the mail. This gives you a feel for what's being worked on
and what's not, who knows what they're talking about and who
doesn't, and what snags are troubling other users. This is
important so you can ask senior developers PRIVATELY when you
have questions relating to The Code - unless you genuinely
believe that a lot of list subscribers also want the
answer. Also, some of the news gateways appear to be brutally
broken, randomly mixing messages from different linux lists like
a cypherpunk remailer gone mad. I recommend going straight to
the source: send 'help' to mailto:majordomo@vger.rutgers.edu

I quickly got over the idea that I could learn everything about
the kernel. Last time I looked, it was over 600,000 lines of
source. I can muck around with SCSI and network device drivers,
I understand the mid level SCSI code, and I've got a reasonably
good handle on the scheduler. That leaves high level
networking, filesystems, the buffer cache and memory management,
to name a few, ABOUT WHICH I HAVEN'T A CLUE. Pick an area you
want to diddle with, and concentrate on that. If you don't
believe me, grab a dictionary and look up 'hubris'.

I read most (some?) of the important stuff in Documentation/
(you should read it all) and then: I dove into the code,
wholeheartedly, for nights (days?) at a time. Pick
drivers. Concentrate on the simple ones - you want concepts, not
nasty workarounds for buggy hardware. Try 'wc *.c|sort' in your
favorite directory. Pick ones that look well formatted and well
commented, and see how they're written and how they interact
with the higher level stuff. Go into each subdirectory in the
whole linux/ tree, and learn what lives there. You should be
able to identify what's what from the stuff you read in those
books. Note especially mm/ and kernel/, along with their
counterparts under arch/. Here lie most of the important
functions for juggling memory, interrupts, processes
etcetera. Learn to use grep, find and xargs effectively. If you
have a strong constitution, look in the scripts/ directory and
the Makefiles everywhere to see how the kernel actually gets
built. If you're a bit twiddler at heart, look at the low level
stuff for your favorite architecture under arch/.

If you've still got the lust for knowledge at this point, you
will probably have found 'that special something' that interests
you in the kernel. You will know generally how things work from
the source, and you will know the right people to ask from the
source and the mailing lists. If you have a question, go ahead
and ask it. I've found developers to be very helpful when asked
questions by someone who's obviously studied the sources. Play
around. Recompile. Benchmark. Test.

One thing that's probably overlooked by a lot of Linux people:
BSD, 'the other free UNIX'. I can't even tell you the difference
between FreeBSD and NetBSD, but for my purposes, I don't
care. They're available free on the net or a CD, just like Linux
<URL:http://ftp.freebsd.org> and <URL:http://www.freebsd.org>.
If you're stumped by something in Linux, seeing how BSD does it
is often helpful, especially for device drivers. Also (ahem) BSD
code sometimes seems to be commented and formatted somewhat
better. I don't run it, I just look at the source.

At this stage your hats will no longer fit, and your dog will
have run off with your girlfriend. No matter, because you'll be
able to ask, and sometimes answer, intelligent questions about
kernel design, in your particular specialty areas. You'll be
fixing insidious bugs, improving performance, and posting things
like 'this patch is from memory and untested, but it will solve
your problem on 2.1.87: [proper patch syntax]'

I'm not at this stage yet, and I've been working at it for a
while. That's why I usually post answers to questions like
'where do I begin' rather than 'why did it hang'. The above is
working for me, it might work for you. May the Source be With
You, Always."

= A. = Appendix A - Maintainers

This policy and FAQ is currently maintained by Frohwalt Egerer
<URL:mailto:froh@iconsult.com>. For communication concerning this
document please use <URL:mailto:kernelfaq@iconsult.com>, that mail
alias will always point to the current maintainer.

The policy is created from input on the linux kernel mailing list.
If desired by members of the list a vote will be held to ratify
the policy.

Thanks to David A Rusling <URL:mailto:rusling@linux.reo.dec.com>
for providing the foundation to section one. Thanks to Colin
Plumb <URL:mailto:colin@nyx.net> who refined my proposal for
section one using his fine taste of language.

Thanks to Cameron MacKinnon <URL:mailto:mackin@interlog.com> for
his really great article on getting started with kernel
development which I adopted into this document.

Thanks to Doug Ledford <URL:mailto:dledford@dialnet.net> for his
excellent description on how to hunt down filesystem corruption

Thanks to Eric Hoeltzel <URL:mailto:eric@dogbert.sitewerks.com>
for the enormous amount of suggestions.

Thanks to Evgeny Rodichev <URL:maito:er@sai.msu.su> for providing
the ver_linux shell script.

And thanks to W. Reilly Cooley, Kevin Fenzi, Gabriel Paubert, Marc
Merlin, Tethys, Antoine Reid, Sebastian Benoit, Regis Duchesne,
Riccardo Facchetti, J. Sean Connel, Seth M. Landsman, Martin
Radford, James Mastros, Nicholas J. Leon, E.Rodichev, Antoine
Reid, Ben Clifford, Melissa Johnson, Dave Wreski, Greg Patterson,
Keith Rohrer, Roch-Alexandre Nomine-Beguin, Raymo
<slk9q@cc.usu.edu>, Elliot Lee, Greg Alexander, Billy Harvey,
Harald Milz, John Carter, Janos Farkas, Tony Gale, Garst R. Reese,
Peter P. Eiserloh, Axel Boldt and all that I forgot to mention for
their input, suggestions and articles on the mailing list. This
FAQ would not exist without their help.

The quote of George B. Shaw in section 1.4 might not be
accurate. I heard it on German TV, remembered it for a few weeks
and translated it back to English for this FAQ.

= B. = Appendix B - Linux Kernel Mailing List Bug Report Form

Please use the following form to report bugs to the Linux kernel
mailing list. Having a standardized bug report form makes it
easier for you not to overlook things, and easier for the
developers to find just the little tad of information they're
really interested in.

First run the ver_linux script included at the end of this
Appendix or at <URL:ftp://ftp.sai.msu.su//sai2/ftp/pub/Linux/ver_linux>
It checks out the version of some important subsystems.

Use that information to fill in all fields of the bug report form,
and post it to the mailing list with a subject of "ISSUE: <one
lime summary from [1.]>" for easy identification by the developers

[1.] One line summary of the problem:
[2.] Full description of the problem/report:
[3.] Keywords (i.e., modules, networking, kernel):
[4.] Kernel version (from /proc/version):
[5.] Output of Oops.. message with symbolic information resolved
(see Kernel Mailing List FAQ, Section 1.5):
[6.] A small shell script or example program which triggers the
problem (if possible)
[7.] Environment
[7.1.] Software (add the output of the ver_linux script here)
[7.2.] Processor information (from /proc/cpuinfo):
[7.3.] Module information (from /proc/modules):
[7.4.] SCSI information (from /proc/scsi/scsi):
[7.5.] Other information that might be relevant to the problem
(please look in /proc and include all information that you
think to be relevant):
[X.] Other notes, patches, fixes, workarounds:

ver_linux (by Evgeny Rodichev <URL:mailto:er@sai.msu.su>

# Before running this script please ensure that your PATH is
# typical as you use for compilation/istallation. I use
# /bin /sbin /usr/bin /usr/sbin /usr/local/bin, but it may
# differs on your system.
echo '-- Versions installed: (if some fields are empty or looks'
echo '-- unusual then possibly you have very old versions)'
uname -a
insmod -V 1>/tmp/ver_linux.tmp 2>>/tmp/ver_linux.tmp
awk 'NR==1{print "Kernel modules ",$NF}' /tmp/ver_linux.tmp
rm -f /tmp/ver_linux.tmp
echo "Gnu C " `gcc --version`
ld -v 2>&1 | awk -F\) '{print $1}' | awk \
'/BFD/{print "Binutils ",$NF}'
ls -l `ldd /bin/sh | awk '/libc/{print $3}'` | awk -F. \
'{print "Linux C Library " $(NF-2)"."$(NF-1)"."$NF}'
ldd -v | awk '{print "Dynamic Linker (ld.so)", $3}'
ls -l /usr/lib/libg++.so | awk -F. \
'{print "Linux C++ Library " $4"."$5"."$6}'
ps --version 2>&1 | awk 'NR==1{print "Procps ", $NF}'
mount --version | awk -F\- '{print "Mount ", $NF}'
netstat --version | awk \
'NR==1{if ($5 != "") { n=split($5,buf,"-"); ver=buf[n]; done=1 }}
NR==2{if (done != 1) ver=$3 }
END{print "Net-tools ",ver}'
loadkeys -h 2>&1 | awk 'NR==1{print "Kbd ",$3}'
expr --v | awk '{print "Sh-utils ", $NF}'

= C. = Appendix C - Unresolved Issues

> "I have recently found a need for an encrypted fs, I have
> however had trouble finding any ones that meet my needs."

=> Which encrypted fs implementations are out there, kernel and
userspace versions?

= D. = Appendix D - Change Log

$Log: draft,v $
Revision 1.11 1997/04/10 10:24:01 cvs
Consistent layout (use 2 spaces between sentences)
Added more information on unsubscribing
Added examples how to do kernel diffs
Added SYN Flooding information
Added P6 Local APIC Information
Imported ver_linux update by Evgeny Rodichev

Revision 1.10 1997/04/10 07:29:19 cvs
Contents updated automatically

Revision 1.9 1997/04/07 05:44:23 cvs
Added a revision header to the top of the draft. Otherwise 1.9 is
equivalent to 1.8

Revision 1.8 1997/04/07 05:40:09 cvs
Imported yet another set of suggestions by Eric.
Imported the ver_linux data collection script of Evgeny Rodichev.

Revision 1.7 1997/04/07 04:32:48 cvs
FAQ is available on http://kernelfaq.iconsult.com from now on.

Revision 1.6 1997/04/06 22:05:07 cvs
Imported lots of e-mailed spelling changes for the parts added in 1.5
Elaborated a bit more on some sections
First draft of the Bug Report Form
Included, updated and corrected a number of resources
Started to use '=' markers so grep will build the table of contents for me

Revision 1.5 1997/04/06 02:43:07 cvs
Fixed typo in Newsgroups: line. Feeling sheepish.

Revision 1.4 1997/04/06 02:41:29 cvs
Imported spelling and stylistic corrections
Elaborated on bug reports (section 1.5.)
Included secion 1.6. "Kernel patches"
Added some new resources to section 2
Added section 3, and 3.1 (common problems) and move the 'getting
started' text to 3.2.
Added a changelog (maintained by cvs)

Revision 1.1-1.3 "long ago"
Early drafts, 1.3 was not released to the public.

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