user.tex

linux 的引导程序源码The Microsoft&reg Windows&reg Software Development Kit (SDK) provides the documentation

sectors have to be altered.

Please refer to the documentation accompanying the LOADLIN package for
installation instructions and further details.


\subsubsection{\LILO\ started by DOS-MBR}

%%beginskip
\bootthree{DOS-MBR \sep LILO \sep Linux \\
  \branch {\rm other OS} \empty}
%%endskip
%:\begin{verbatim}
%;+-------------------------------------------------------+
%;| Master Boot Record    Boot sector    Operating system |
%;|-------------------------------------------------------|
%;| DOS-MBR ------------> LILO --------> Linux            |
%;|                  ---> other OS                        |
%;+-------------------------------------------------------+
%:\end{verbatim}

This is a ``safe'' \LILO\ setup: \LILO\ is booted by the DOS-MBR. No other boot
sectors have to be touched. If the other OS (or one of them, if there are
several other operating systems being used) should be booted without
using \LILO, the other
partition has to be marked ``active'' with \name{fdisk} or \name{activate}.

Installation:
\begin{itemize}
  \item install \LILO\ with its boot sector on the Linux partition.
  \item use \name{fdisk} or \name{activate} to make that partition active.
  \item reboot.
\end{itemize}

Deinstallation:
\begin{itemize}
  \item make a different partition active.
  \item install whatever should replace \LILO\ and/or Linux.
\end{itemize}


\subsubsection{Several alternate branches}

%%beginskip
\bootfour{DOS-MBR \sep MS-DOS \sep COMMAND.COM \empty \\
  \empty \branch LOADLIN \sep Linux \\
  \branch LILO \sep Linux \empty \\
  \empty \branch MS-DOS \cont \empty}
%%endskip
%:\begin{verbatim}
%4+------------------------------------------------------------+
%4| Master Boot Record    Boot sector    Operating system      |
%4|------------------------------------------------------------|
%4| DOS-MBR ------------> MS-DOS ------> COMMAND.COM           |
%4|                                 ---> LOADLIN ------> Linux |
%4|                  ---> LILO --------> Linux                 |
%4|                                 ---> MS-DOS --- ...        |
%4+------------------------------------------------------------+
%:\end{verbatim}

An extended form of the above setup: the MBR is not changed and both branches
can either boot Linux or MS-DOS. (\LILO\ could also boot other
operating systems.)


\subsubsection{\LILO\ started by \name{BOOTACTV}\protect\footnotemark}
\footnotetext{Other, possibly better known boot switchers, e.g. \name{OS/2
BootManager} operate in a similar way. The installation procedures typically
vary.}

%%beginskip
\bootthree{BOOTACTV \sep LILO \sep Linux \\
  \branch {\rm other OS} \empty}
%%endskip
%:\begin{verbatim}
%;+-------------------------------------------------------+
%;| Master Boot Record    Boot sector    Operating system |
%;|-------------------------------------------------------|
%;| BOOTACTV -----------> LILO --------> Linux            |
%;|                  ---> other OS                        |
%;+-------------------------------------------------------+
%:\end{verbatim}

Here, the MBR is replaced by \name{BOOTACTV} (or any other interactive boot
partition selector) and the choice between Linux and the
other operating system(s) can be made at boot time. This approach should be
used if \LILO\ fails to boot the other operating system(s).\footnote{%
And the author would like to be notified if booting the other operating
system(s) doesn't work with \LILO, but if it works with an other boot partition
selector.}

Installation:
\begin{itemize}
  \item boot Linux.
  \item make a backup copy of your MBR on a floppy disk, e.g. \\
    \verb"dd if=/dev/hda of=/fd/MBR bs=512 count=1"
  \item install \LILO\ with the boot sector on the Linux partition.
  \item install \name{BOOTACTV} as the MBR, e.g. \\
    \verb"dd if=bootactv.bin of=/dev/hda bs=446 count=1"
  \item reboot.
\end{itemize}

Deinstallation:
\begin{itemize}
  \item boot Linux.
  \item restore the old MBR, e.g. \\
    \verb"dd if=/MBR of=/dev/hda bs=446 count=1" \\
    or \verb"FDISK /MBR" under MS-DOS.
\end{itemize}

If replacing the MBR appears undesirable and if a second Linux partition
exists (e.g. \path{/usr}, \emphasize{not} a swap partition), \name{BOOTACTV}
can be merged with
the partition table and stored as the ``boot sector'' of that partition.
Then, the partition can be marked active to be booted by the DOS-MBR.

Example:
\begin{verbatim}
# dd if=/dev/hda of=/dev/hda3 bs=512 count=1
# dd if=bootactv.bin of=/dev/hda3 bs=446 count=1
\end{verbatim}

\emphasize{WARNING:} Whenever the disk is re-partitioned, the merged boot
sector on that ``spare'' Linux partition has to be updated too.


\subsubsection{\LILO\ alone}

%%beginskip
\boottwo{LILO \sep Linux \\
  \branch {\rm other OS}}
%%endskip
%:\begin{verbatim}
%;    +----------------------------------------+
%;    | Master Boot Record    Operating system |
%;    |----------------------------------------|
%;    | LILO ---------------> Linux            |
%;    |                  ---> other OS         |
%;    +----------------------------------------+
%:\end{verbatim}

\LILO\ can also take over the entire boot procedure. If installed as the MBR,
\LILO\ is responsible for either booting Linux or any other OS. This approach
has the disadvantage, that the old MBR is overwritten and has to be restored
(either from a backup copy, with \verb"FDISK /MBR" on recent versions of
MS-DOS or by overwriting it with something like \name{BOOTACTV}) if Linux
should ever be removed from the system.

You should verify that \LILO\ is able to boot your other operating system(s)
before relying on this method.

Installation:
\begin{itemize}
  \item boot Linux.
  \item make a backup copy of your MBR on a floppy disk, e.g. \\
    \verb"dd if=/dev/hda of=/fd/MBR bs=512 count=1"
  \item install \LILO\ with its boot sector as the MBR.
  \item reboot.
\end{itemize}

Deinstallation:
\begin{itemize}
  \item boot Linux.
  \item restore the old MBR, e.g. \\
    \verb"dd if=/fd/MBR of=/dev/hda bs=446 count=1"
\end{itemize}

If you've installed \LILO\ as the master boot record, you have to
explicitly specify the boot sector (configuration variable
\craw{boot=}$\ldots$) when updating the map. Otherwise, it
will try to use the boot sector of your current root partition, which
will usually work, but it will probably leave your system unbootable.


\subsubsection{Names}

The following names have been used to describe boot sectors or parts of
operating systems:

\begin{description}
  \item[``DOS-MBR''] is the original MS-DOS MBR. It scans the partition
    table for a partition that is marked ``active'' and loads the boot
    sector of that partition. Programs like MS-DOS' \name{FDISK}, Linux
    \name{fdisk} or \name{activate} (accompanies \LILO)
    can change the active marker in the partition table.
  \item[``MS-DOS''] denotes the MS-DOS boot sector that loads the other parts
    of the system (\path{IO.SYS}, etc.).
  \item[``COMMAND.COM''] is the standard command interpreter of MS-DOS.
  \item[``LOADLIN''] is a program that loads a Linux
    kernel image from an
    MS-DOS partition into memory and executes it. It is usually invoked
    from \path{CONFIG.SYS} and is used in combination with a \path{CONFIG.SYS}
    configuration switcher, like BOOT.SYS.\footnote{
      \name{LOADLIN} is available for anonymous FTP from \\
      \path{ftp://tsx-11.mit.edu/pub/linux/dos\_utils/lodlin\meta{n}.tar.gz} \\
      \path{ftp://sunsite.unc.edu/pub/Linux/system/boot/dualboot/lodlin\meta{n}%
.tgz} \\
      \name{BOOT.SYS} is available for anonymous FTP from \\
      \path{ftp://ftp.funet.fi/pub/Linux/tools/boot142.zip}}
  \item[``LILO''] can either load a Linux kernel or the boot sector of any
    other operating system. It has a first stage boot sector that
    loads the remaining parts of \LILO\ from various locations.\footnote{%
      \LILO\ can be found in \\
      \path{ftp://tsx-11.mit.edu/pub/linux/packages/lilo/lilo-\meta{n}.tar.gz}
	\\
      \path{ftp://sunsite.unc.edu/pub/Linux/system/boot/lilo/lilo-%
\meta{n}.tar.gz} \\
      \path{ftp://lrcftp.epfl.ch/pub/linux/local/lilo/lilo-\meta{n}.tar.gz}}
  \item[``BOOTACTV''] permits interactive selection of the partition from
    which the boot sector should be read. If no key is pressed within a
    given interval, the partition marked active is booted. \name{BOOTACTV} is
    included in the \name{pfdisk} package. There are also several similar
    programs, like PBOOT and OS-BS.\footnote{\name{pfdisk} is available for
      anonymous FTP from \\
      \path{ftp://sunsite.unc.edu/pub/Linux/utils/disk-management/pfdisk.tar.Z}
	or \\
      \path{ftp://ftp.funet.fi/pub/Linux/tools/pfdisk.tar.Z} \\
      PBOOT can be found in \\
      \path{ftp://ftp.funet.fi/pub/Linux/tools/pboot.zip}}
\end{description}


\subsection{Choosing the ``right'' boot concept}

Although \LILO\ can be installed in many different ways, the choice is
usually limited by the present setup and therefore,
typically only a small number of configurations which fit naturally
into an existing system remains. The following sections describe various
possible cases. See also section \ref{broken}.

The configuration file \path{/etc/lilo.conf} for the examples
could look like this:

\begin{verbatim}
boot = /dev/hda2
compact
image = /vmlinuz
image = /vmlinuz.old
other = /dev/hda1
  table = /dev/hda
  label = msdos
\end{verbatim}

It installs a Linux kernel image (\path{/vmlinuz}),
an alternate Linux kernel image (\path{/vmlinuz.old}) and
a chain loader to boot MS-DOS from \path{/dev/hda1}. The option \craw{compact}
on the second line instructs the map installer to optimize loading.

In all examples, the names of the IDE-type hard disk devices
(\path{/dev/hda$\ldots$}) are used. Everything applies to other disk types
(e.g. SCSI disks; \path{/dev/sda$\ldots$}) too.


\subsubsection{BIOS restrictions}
\label{broken}

Nowadays, an increasing number of systems is equipped with comparably large
disks or even with multiple disks. At the time the disk interface of the
standard PC BIOS has been designed (about 16 years ago), such configurations
were apparently considered to be too unlikely to be worth supporting.

The most common BIOS restrictions that affect \LILO\ are the limitation to
two hard disks and the inability to access more than 1024 cylinders per
disk. \LILO\ can detect both conditions, but in order to work around the
underlying problems, manual intervention is necessary.

The drive limit does not exist in every BIOS. Some modern motherboards
and disk controllers are equipped with a BIOS that supports more (typically
four) disk drives. When attempting to access the third, fourth, etc. drive,
\LILO\ prints a warning message but continues. Unless the BIOS really
supports more than two drives, the system will \emphasize{not} be able to
boot in that case.\footnote{However, if only ``unimportant'' parts of the
system are located on the ``high'' drives, some functionality may be
available.}

The cylinder limit is a very common problem with IDE disks. There, the
number of cylinders may already exceed 1024 if the drive has a capacity
of more than 504 MB. Many SCSI driver BIOSes present the disk geometry
in a way that makes the limit occur near 1 GB. Modern disk controllers
may even push the limit up to about 8 GB. All cylinders beyond the
1024th are inaccessible for the BIOS. \LILO\ detects this problem and
aborts the installation (unless the \craw{linear} option is used, see
section \ref{cfgglo}).

Note that large partitions that only partially extend into the ``forbidden
zone'' are still in jeopardy even if they appear to work at first, because
the file system does not know about the restrictions and may allocate
disk space from the area beyond the 1024th cylinder when installing new
kernels. \LILO\ therefore prints a warning message but continues as long
as no imminent danger exists.

There are four approaches of how such problems can be solved:
\begin{itemize}
  \item use of a different partition which is on an accessible disk and
    which does not exceed the 1024 cylinder limit. If there is only a DOS
    partition which fulfills all the criteria, that partition can be
    used to store the relevant files. (See section \ref{viados}.)
  \item rearranging partitions and disks. This is typically a destructive
    operation, so extra care should be taken to make good backups.
  \item if the system is running DOS or Windows 95, \name{LOADLIN} can be
    used instead of \LILO.
  \item if all else fails, installation of a more capable BIOS, a different
    controller or a different disk configuration.
\end{itemize}

\LILO\ depends on the BIOS to load the following items:
\begin{itemize}
  \item \path{/boot/boot.b}
  \item \path{/boot/map} (created when running \path{/sbin/lilo})
  \item all kernels
  \item the boot sectors of all other operating systems it boots
  \item the startup message, if one has been defined
\end{itemize}

Normally, this implies that the Linux root file system should be in the
``safe'' area. However, it is already sufficient to put all kernels into
\path{/boot} and to either mount a ``good'' partition on \path{/boot} or
to let \path{/boot} be a symbolic link pointing to or into such a
partition.

See also \path{/usr/src/linux/Documentation/ide.txt} (or
\path{/usr/src/linux/drivers/block/README.ide} in older kernels) for a detailed
description of problems with large disks.


\subsubsection{One disk, Linux on a primary partition}

If at least one primary partition of the first hard disk is used as a
Linux file system (\path{/}, \path{/usr}, etc. but \emphasize{not} as a swap
partition), the \LILO\ boot sector should be stored on that partition
and it should be booted by the original master boot record or by a
program like \name{BOOTACTV}.

%%beginskip
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