This is a draft for a use policy and FAQ for the kernel mailing
list. If it is accepted by the list I'd volunteer to send it to the
list regularly. The contents of this draft are taken from the linux
kernel mailing list.
I will put a HTMLized version on our web server later in the process.
Please comment on it; 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
froh@iconsult.com, and they will be included in the next version of
the draft. English is not my native language, so expect a lot of
these.
Issues to resolve:
- I have to perform some more research on online resources.
- What is the current distribution mechanism for the list? Besides
the now-closed news gateway, are there any more ways to subscribe
to the list than vger?
- There seems to be a web page discussing signal 11. What's the URL?
- Would a 'kernel mailing list bug report form' be a good idea? It
would ask questions regarding the hard- and software of the buggy
system. (Maybe a shell script that collects information from /proc
and automatically includes it in the bug report would be cool.)
- Which testing tools for ruling out hardware problems are available?
What's the home page for memtest-86?
- How do I tell emacs to insert spaces insert of tabs when I hit the
tab key in fundamental mode? Gosh, I got to read up on emacs modes
for text editing rather than hacking C++ source ...
- What's the status and official site for the Linux software map?
www.boutell.com seems to be a bit dated (April 96).
- Learn to do less typos when typing ...
Resolved issues (please still comment on those ...)
- I have to read up on the official quoting for URLs in plain text.
-> I was told <URL:http://foo.bar.baz.qux> and
<URL:news:foo.bar.baz> is OK. (note the // left out with news)
- Shall the FAQ be posted monthly, biweekly or weekly?
-> Most answers I got prefer biweekly.
- Shall the FAQ be sent to new subscribers of the mailing list?
-> I'll contact the mailing list maintainer when the FAQ is
finished and ask him to configure majordomo to send the
document to new subscribers of the list.
- Shall this article be posted to comp.os.linux.answers regularly?
-> Yes, it will be posted there, as well as in all other appropriate
*.answers newsgroups.
- Shall there be an abbreviated version of this FAQ just containing
section one? IMO people are easily scared by documents longer
than a few pages.
-> The answers I got suggested not to do so. I still favor the idea
of having a _short_ mailing list policy document. (This file is
three days old and already has over 800 lines.)
DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT
=======================================================================
CONTENTS
0. Introduction
1. The kernel mailing list
1.1 Topic
1.2 Off topic
1.3 Etiquette
1.4 How to get off this mailing list
2. Online resources
2.1 Kernel resources
2.1.1. The Linux Kernel HOWTO - How to compile a kernel
2.1.2. Linux v2 Information
2.1.3. The kernel hackers guide
2.1.4. Writing device drivers
2.1.5. The Linux Wish List
2.1.6. IRC
2.1.7. Linux Journal
2.1.8. Books
2.2 Other points of interest
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
3.2. How to get started on kernel development
A. Appendix A - Maintainers
B. Appendix B - Change Log
0. Introduction
This is the Linux kernel mailing list FAQ and usage policy. It is
posted to the mailing list regularly. Note that the FAQ is not so
much a FAQ but more are 'Frequent answers collection'.
The first section contains information about the kernel mailing list.
Please read it before posting to the list or be ready to be
flamed.
1. The kernel mailing list
1.1. How do I get off of this mailing list ???
Send mail containing "unsubscribe linux-kernel" to
majordomo@vger.rutgers.edu
(echo "unsubscribe linux-kernel" | mail majordomo@vger.rutgers.edu)
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.
1.3. Off-topic
Please do not ask basic installation questions on this list. If
you are unclear on 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
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. A good strategy is to wait a day after
writing something before posting. The very same information may
hit the list during that time.
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 and lead himself to more
deeply insights.
There's a saying that is attributed to George B. Shaw:
"Most people think about twice a year. I got famous by thinking
once a week."
(I heard this on TV in German, remembered it for a few weeks and
translated it from memory. I'd be grateful if some nice soul
informed <URL:mailto:kernelfaq@iconsult.com> me about the
original wording and place where to find it.)
1.5. Bug Reports
There are a few things to consider before reporting kernel error
messages:
- Think twice!
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 and even
that a bug reporter trying to be too clever optimized away that
bit of relevant information. 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.
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'.
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 boards.
- 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
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 a
maintainer for a specific Linux subsystem.
1.6. Kernel patches
Please use unified (-u) diff format when submitting kernel
patches, 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 round)
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.
<Please note that I'm still in the process of collecting these,
the list is still incomplete ...>
2.1. Kernel resources
2.1.1. The Linux Kernel HOWTO - How to compile a kernel
2.1.2. Linux v2 Information
<URL:http://www.ecsnet.com>
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. Two
thumbs up.
2.1.3. The kernel hackers guide
<URL:http://www.redhat.com:8080/HyperNews/get/khg.html>
Once upon a time it was a paper document but due to the 'moving
target' nature of a constantly developed kernel it now is
completely web-based, using a hyper-news system so users can
add input.
2.1.4. Writing device drivers
<URL:http://www.redhat.com/~johnsonm/devices.html>
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.
2.1.5. The Linux Wish List
<URL:http://www.cs.uml.edu/~acahalan/linux/wishlist.html>
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
project.
2.1.6. IRC
There is said to be online support on IRC, nameley servers
irc.linpeople.org (207.16.36.11) or vinge.linpeople.org. Look for
the channels #help or #natter.
(I can't decide if to put this in "kernel resources" or in "other
points of interest". Would users of that service please let me
know about the 'kernel hacker percentage' on these servers?
<URL:mailto:kernelfaq@iconsult.com>. Is there an URL syntax for
IRC connections?)
2.1.7. Linux Journal
From <URL:http://www.redhat.com:8080/HyperNews/get/devices/devices.html>:
"Linux Journal <URL:http://www.ssc.com/lj/> has had a long-running
series of articles called Kernel Korner which, despite the wacky
name, has had quite a bit of useful information in it. Some of the
articles from that column may be available on the web; most of
them are available for purchase as back issues. One particularly
useful series of articles, which focussed in far more detail than
my 30 minute talk on the subject of kernel runtime-loadable
modules, was in issues 23, 24, 25, 26, and 28. They were written
by Alessandro Rubini and Georg v. Zezschwitz. Issue 29 is slated
(as of this writing) to have an article on writing network device
drivers, written by Alan Cox. Issues 9, 10, and 11 have a series
that I wrote on block device drivers."
2.1.8. Books
There aren't any book reviews in this section yet. You might want
to look at Cameron McKinnon's article in Section 4 (How to get
started on kernel development). That article discusses some books.
If you have read a book related to Linux (or Unix) kernel
development please send a review to <URL:mailto:kernelfaq@iconsult.com>
so it can be added to the FAQ.
2.2. Other points of interest
These are other general resources.
The Linux documentation project:
<URL:http://www.caldera.com/LDP>
<URL:http://www.sunsite.com/LDP>
The LDP contains _loads_ of Linux documentation, including, but
not limited to the HOWTOS, FAQs, manpages and various guides.
The Linux software map:
<URL:http://www.boutell.com>
This seems to be a bit out of date. (April 96)
Other URLs:
<URL:ftp://ftp.cs.helsinki.fi/pub/Software/Linux/Kernel/>
Linux kernel
<URL:http://www.ssc.com/linux/web.html> Linux on the Web
<URL:http://www.boutell.com/lsm/> Linux software map
<URL:http://sunsite.unc.edu/pub/Linux/> Sunsite Linux archive
<URL:http://sunsite.unc.edu/paulc/incoming.html>
Find new files on Sunsite
<URL:http://www.crynwr.com/kchanges/>
Linux Kernel change summary
<URL:http://sunsite.unc.edu/linux-source>
Linux Source Navigator
<URL:http://torgo.ml.org/las> Linux archive search
<URL:http://cesdis1.gsfc.nasa.gov:80/linux/drivers/>
Linux Network drivers
<URL:http://www.uk.linux.org/SMP/title.html>Linux SMP project
The Linux news groups:
<URL:news:comp.os.linux.advocacy>
Benefits of Linux compared to other operating systems
<URL:news:comp.os.linux.announce>
Announcements important to the Linux community. (Moderated)
<URL:news:comp.os.linux.answers>
FAQs, HOWTOs, READMEs, etc. about Linux. (Moderated)
<URL:news:comp.os.linux.development.apps>
Writing Linux applications, porting to Linux
<URL:news:comp.os.linux.development.system>
Linux kernels, device drivers, modules
<URL:news:comp.os.linux.hardware>
Hardware compatibility with the Linux operating system
<URL:news:comp.os.linux.m68k>
Linux operating system on 680x0 Amiga, Atari, VME
<URL:news:comp.os.linux.misc>
Linux-specific topics not covered by other groups
<URL:news:comp.os.linux.networking>
Networking and communications under Linux
<URL:news:comp.os.linux.setup>
Linux installation and system administration
<URL:news:comp.os.linux.x>
Linux X Window System servers, clients, libs and fonts
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
users Signal 11 trouble. A kernel is a complex thing of software,
all errors happening in the kernel or in hardware below it might
cause every thinkable and unthinkable kind of problem. Errors
propagate in unforseeable ways. There are hardware problems with
show up only on Linux while Win95, NT, OS/2, Doom and Quake run
fine on the same computer. Everything running except Linux does
not prove Linux is buggy. 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, even just like adding a drop of tabasco sauce to a
witches 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."
Before starting another round on the ext2fs file corruption thread
in the kernel mailing list you might want to check all other
possible sources. Often a 'Linux sucks' thread ends with the
original poster finding a problem his computer's hardware or
software installation.
For example I had a problem with ext2fs file system corruption once
myself. Asking on the linux newsgroups I found out others had
experienced similar problems, and all had a common factor: The
same brand and model of hard drive. My (then) brand new Conner
CFP1060S had a firmware bug. Discussing with other people that had
the same problem was the way to find a hard to locate bug in the
drive's firmware.
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 to cause
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.
- 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 test 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
aggressive
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."
I'd like to add some real life examples to the last sentence of
Doug's article: In the case of the faulty drive firmware
mentioned above slowing down e2fsck (by deliberately adding
delays it at strategic places in the e2fsck source) the problem
vanished. In the project I earn money with I had a similar
example right this week. (A terminal adapter that drops all
received characters for a few milliseconds after a CONNECT
response. On Solaris the problem went unnoticed due to Solaris
being not exactly fast regarding character I/O. This resulted in
a 'Linux sucks!' situation; a certain software just refused to
work on Linux, because of it's data stream being converted to
bogons in some device connected to the serial port.)
- Use debugging tools to check your system. A list of such tools
(both free and commercial) will be added here. If you think a
particular tool shall be listed please mail to
<URL:mailto:kernelfaq@iconsult.com>
3.1.2. 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 got different
trouble; the procedures mentioned in the FAQ will probably help
finding your problem, too.
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
date.
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 stared with kernel development
which I adopted into this document.
Thanks to Doug Ledford <URL:mailto:dledford@dialnet.net> for his
excellent description how to hunt down filesystem corruption
problems.
And thanks to W. Reilly Cooley, Eric Hoeltzel, Kevin Fenzi,
Gabriel Paubert, Marc Merlin, Tethys "SYSTEM ADMIN" X, Antoine
Reid, Doug Ledford, Sebastian Benoit, Regis Duchesne, Riccardo
Facchetti, J. Sean Connel, Seth M. Landsman, Martin Radford, James
Mastros, Nicholas J. Leon, E.Rodichev, Antoine Reid 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.
B. Appendix B - Change Log
$Log: draft,v $
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:
Early drafts, 1.3 was not released to the public.