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README
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Linux kernel release 1.2.xx
These are the release notes for linux version 1.2. Read them carefully,
as they tell you what this is all about, explain how to install the
kernel, and what to do if something goes wrong.
WHAT IS LINUX?
Linux is a Unix clone for 386/486-based PCs written from scratch by
Linus Torvalds with assistance from a loosely-knit team of hackers
across the Net. It aims towards POSIX compliance.
It has all the features you would expect in a modern fully-fledged
Unix, including true multitasking, virtual memory, shared libraries,
demand loading, shared copy-on-write executables, proper memory
management and TCP/IP networking.
It is distributed under the GNU General Public License - see the
accompanying COPYING file for more details.
DOCUMENTATION:
- there is a lot of documentation available both in electronic form on
the internet and in books, both Linux-specific and pertaining to
general UNIX questions. I'd recommend looking into the documentation
subdirectories on any Linux ftp site for the LDP (Linux Documentation
Project) books. This README is not meant to be documentation on the
system: there are much better sources available.
INSTALLING the kernel:
- If you install the full sources, do a
cd /usr/src
gzip -cd linux-1.2.XX.tar.gz | tar xfv -
to get it all put in place. Replace "XX" with the version number of the
latest kernel.
- Installing by patching is not worth the effort because the full set of
patches is bigger than a new kernel distribution. Instead, get the
latest full source archive and install as above. Then, get all newer
patch files, and do
cd /usr/src
gzip -cd patchXX.gz | patch -p0
(repeat xx for all versions bigger than the version of your current
source tree, _in_order_) and you should be ok. You may want to remove
the backup files (xxx~ or xxx.orig), and make sure that there are no
failed patches (xxx# or xxx.rej). If there are, either you or me has
made a mistake.
- make sure your /usr/include/linux and /usr/include/asm directories
are just symlinks to the kernel sources:
cd /usr/include
rm -rf linux
rm -rf asm
ln -s /usr/src/linux/include/linux .
ln -s /usr/src/linux/include/asm .
- make sure you have no stale .o files and dependencies lying around:
cd /usr/src/linux
make mrproper
You should now have the sources correctly installed.
CONFIGURING the kernel:
- do a "make config" to configure the basic kernel. "make config"
needs bash to work: it will search for bash in $BASH, /bin/bash and
/bin/sh (in that order), so hopefully one of those is correct.
NOTES on "make config":
- having unnecessary drivers will make the kernel bigger, and can
under some circumstances lead to problems: probing for a
nonexistent controller card may confuse your other controllers
- compiling the kernel with "-m486" for a number of 486-specific
will result in a kernel that still works on a 386: it may be
slightly larger and possibly slower by an insignificant amount,
but it should not hurt performance.
- A kernel with math-emulation compiled in will still use the
coprocessor if one is present: the math emulation will just
never get used in that case. The kernel will be slightly larger,
but will work on different machines regardless of whether they
have a math coprocessor or not.
- the "kernel hacking" configuration details usually result in a
bigger or slower kernel (or both), and can even make the kernel
less stable by configuring some routines to actively try to
break bad code to find kernel problems (kmalloc()). Thus you
should probably answer 'n' to the questions for a "production"
kernel.
- Check the top Makefile for further site-dependent configuration
(default SVGA mode etc).
- Finally, do a "make dep" to set up all the dependencies correctly.
COMPILING the kernel:
- make sure you have gcc-2.5.8 or newer available. It seems older gcc
versions can have problems compiling newer versions of linux. If you
upgrade your compiler, remember to get the new binutils package too
(for as/ld/nm and company). Do not use gcc-2.6.0; it has a few serious
bugs.
- do a "make zImage" to create a compressed kernel image. If you want
to make a bootdisk (without root filesystem or lilo), insert a floppy
in your A: drive, and do a "make zdisk". It is also possible to do
"make zlilo" if you have lilo installed to suit the kernel makefiles,
but you may want to check your particular lilo setup first.
- keep a backup kernel handy in case something goes wrong.
- In order to boot your new kernel, you'll need to copy the kernel
image (found in /usr/src/linux/arch/i386/boot/zImage after compilation)
to the place where your regular bootable kernel is found.
For some, this is on a floppy disk, in which case you can "cp
/usr/src/linux/arch/i386/boot/zImage /dev/fd0" to make a bootable
floppy.
If you boot Linux from the hard drive, chances are you use LILO which
uses the kernel image as specified in the file /etc/lilo/config. The
kernel image file is usually /vmlinuz, or /zImage, or /etc/zImage.
To use the new kernel, copy the new image over the old one (save a
backup of the original!). Then, you MUST RERUN LILO to update the
loading map!! If you don't, you won't be able to boot the new kernel
image.
Reinstalling LILO is usually a matter of running /etc/lilo/install.
You may wish to edit /etc/lilo/config to specify an entry for your
old kernel image (say, /vmlinux.old) in case the new one does not
work. See the LILO docs for more information.
After reinstalling LILO, you should be all set. Shutdown the system,
reboot, and enjoy!
If you ever need to change the default root device, video mode,
ramdisk size, etc. in the kernel image, use the 'rdev' program (or
alternatively the LILO boot options when appropriate). No need to
recompile the kernel to change these parameters.
- reboot with the new kernel and enjoy.
IF SOMETHING GOES WRONG:
- if you have problems that seem to be due to kernel bugs, please mail
them to me ([email protected]), and possibly to any other
relevant mailing-list or to the newsgroup. The mailing-lists are
useful especially for SCSI and NETworking problems, as I can't test
either of those personally anyway.
- In all bug-reports, *please* tell what kernel you are talking about,
how to duplicate the problem, and what your setup is (use your common
sense). If the problem is new, tell me so, and if the problem is
old, please try to tell me when you first noticed it.
- if the bug results in a message like
unable to handle kernel paging request at address C0000010
Oops: 0002
EIP: 0010:XXXXXXXX
eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
ds: xxxx es: xxxx fs: xxxx gs: xxxx
Pid: xx, process nr: xx
xx xx xx xx xx xx xx xx xx xx
or similar kernel debugging information on your screen or in your
system log, please duplicate it *exactly*. The dump may look
incomprehensible to you, but it does contain information that may
help debugging the problem. The text above the dump is also
important: it tells something about why the kernel dumped code (in
the above example it's due to a bad kernel pointer)
- in debugging dumps like the above, it helps enormously if you can
look up what the EIP value means. The hex value as such doesn't help
me or anybody else very much: it will depend on your particular
kernel setup. What you should do is take the hex value from the EIP
line (ignore the "0010:"), and look it up in the kernel namelist to
see which kernel function contains the offending address.
To find out the kernel function name, you'll need to find the system
binary associated with the kernel that exhibited the symptom. This is
the file 'linux/vmlinux'. To extract the namelist and match it against
the EIP from the kernel crash, do:
nm vmlinux | sort | less
This will give you a list of kernel addresses sorted in ascending
order, from which it is simple to find the function that contains the
offending address. Note that the address given by the kernel
debugging messages will not necessarily match exactly with the
function addresses (in fact, that is very unlikely), so you can't
just 'grep' the list: the list will, however, give you the starting
point of each kernel function, so by looking for the function that
has a starting address lower than the one you are searching for but
is followed by a function with a higher address you will find the one
you want. In fact, it may be a good idea to include a bit of
"context" in your problem report, giving a few lines around the
interesting one.
If you for some reason cannot do the above (you have a pre-compiled
kernel image or similar), telling me as much about your setup as
possible will help.
- alternately, you can use gdb on a running kernel. (read-only; i.e. you
cannot change values or set break points.) To do this, first compile the
kernel with -g; edit arch/i386/Makefile appropriately, then do a "make
clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
You can now use all the usual gdb commands. The command to look up the
point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
with the EIP value.)
gdb'ing a non-running kernel currently fails because gdb (wrongly)
disregards the starting offset for which the kernel is compiled.