grub.texi

GRUB 0.93的源代码。有人说可以当一个很小的操作系统了

Here, @samp{hd} means it is a hard disk drive. The first integer
@samp{0} indicates the drive number, that is, the first hard disk, while
the second integer, @samp{1}, indicates the partition number (or the
@sc{pc} slice number in the BSD terminology). Once again, please note
that the partition numbers are counted from @emph{zero}, not from
one. This expression means the second partition of the first hard disk
drive. In this case, GRUB uses one partition of the disk, instead of the
whole disk.

@example
(hd0,4)
@end example

This specifies the first @dfn{extended partition} of the first hard disk
drive. Note that the partition numbers for extended partitions are
counted from @samp{4}, regardless of the actual number of primary
partitions on your hard disk.

@example
(hd1,a)
@end example

This means the BSD @samp{a} partition of the second hard disk. If you
need to specify which @sc{pc} slice number should be used, use something
like this: @samp{(hd1,0,a)}. If the @sc{pc} slice number is omitted,
GRUB searches for the first @sc{pc} slice which has a BSD @samp{a}
partition.

Of course, to actually access the disks or partitions with GRUB, you
need to use the device specification in a command, like @samp{root
(fd0)} or @samp{unhide (hd0,2)}. To help you find out which number is a
partition you want, the GRUB command-line (@pxref{Command-line
interface}) options have argument completion. That means that, for
example, you only need to type @samp{root (}, followed by a @key{TAB},
and GRUB will display the list of drives, partitions, or file names, so
it should be quite easy to determine the name of your target partition,
even with minimal knowledge of the syntax.

Note that GRUB does @emph{not} distinguish IDE from SCSI - it simply
counts the drive numbers from zero, regardless of their type. Normally,
any IDE drive number is less than any SCSI drive number, although that
is not true if you change the boot sequence by swapping IDE and SCSI
drives in your BIOS.

Now the question is, how to specify a file? Again, see this example:

@example
(hd0,0)/vmlinuz
@end example

This specifies the file named @samp{vmlinuz}, found on the first
partition of the first hard disk drive. Note that the argument
completion works with file names, too.

That was easy, admit it. Do read the next chapter, to find out how to
actually install GRUB on your drive.


@node Installation
@chapter Installation

First, you need to have GRUB itself properly installed on your system,
(@pxref{Obtaining and Building GRUB}) either from the source tarball, or
as a package for your OS.

To use GRUB, you need to install it on your drive. There are two ways of
doing that - either using the utility @command{grub-install}
(@pxref{Invoking grub-install}) on a UNIX-like OS, or by using the
native Stage 2. These are quite similar, however, the utility might
probe a wrong BIOS drive, so better be careful.

Also, if you install GRUB on a UNIX-like OS, please make sure that you
have an emergency boot disk ready, so that you can rescue your computer
if, by any chance, your hard drive becomes unusable (unbootable).

GRUB comes with boot images, which are normally installed in the
directory @file{/usr/share/grub/i386-pc}. You need to copy the files
@file{stage1}, @file{stage2}, and @file{*stage1_5} to the directory
@file{/boot/grub}. Here the directory where GRUB images are installed
and the directory where GRUB will use to find them are called @dfn{image
directory} and @dfn{boot directory}, respectively.

@menu
* Creating a GRUB boot floppy::
* Installing GRUB natively::
* Installing GRUB using grub-install::
@end menu


@node Creating a GRUB boot floppy
@section Creating a GRUB boot floppy

To create a GRUB boot floppy, you need to take the files @file{stage1}
and @file{stage2} from the image directory, and write them to the first
and the second block of the floppy disk, respectively.

@strong{Caution:} This procedure will destroy any data currently stored
on the floppy.

On a UNIX-like operating system, that is done with the following
commands:

@example
@group
# @kbd{cd /usr/share/grub/i386-pc}
# @kbd{dd if=stage1 of=/dev/fd0 bs=512 count=1}
1+0 records in
1+0 records out
# @kbd{dd if=stage2 of=/dev/fd0 bs=512 seek=1}
153+1 records in
153+1 records out
#
@end group
@end example

The device file name may be different. Consult the manual for your OS.


@node Installing GRUB natively
@section Installing GRUB natively

@strong{Caution:} Installing GRUB's stage1 in this manner will erase the
normal boot-sector used by an OS.

GRUB can currently boot GNU Mach, Linux, FreeBSD, NetBSD, and OpenBSD
directly, so using it on a boot sector should be okay. But generally, it
would be a good idea to back up the first sector of the partition on
which you are installing GRUB's stage1. This isn't as important if you
are installing GRUB on the first sector of a hard disk, since it's easy
to reinitialize it (e.g. by running @samp{FDISK /MBR} from DOS).

If you decide to install GRUB in the native environment, which is
definitely desirable, you'll need to create the GRUB boot disk, and
reboot your computer with it. Otherwise, see @ref{Installing GRUB using
grub-install}, for more details.

Once started, GRUB will show the command-line interface
(@pxref{Command-line interface}). First, set the GRUB's @dfn{root
device}@footnote{Note that GRUB's root device doesn't necessarily mean
your OS's root partition; if you need to specify a root partition for
your OS, add the argument into the command @command{kernel}.} to the
boot directory, like this:

@example
grub> @kbd{root (hd0,0)}
@end example

If you are not sure which partition actually holds these files, use the
command @command{find} (@pxref{find}), like this:

@example
grub> @kbd{find /boot/grub/stage1}
@end example

This will search for the file name @file{/boot/grub/stage1} and show the
devices which contain the file.

Once you've set the root device correctly, run the command
@command{setup} (@pxref{setup}):

@example
grub> @kbd{setup (hd0)}
@end example

This command will install GRUB on the MBR in the first drive. If you
want to install GRUB into the @dfn{boot sector} of a partition instead
of the MBR, specify a partition into which you want to install GRUB:

@example
grub> @kbd{setup (hd0,0)}
@end example

If you install GRUB into a partition or a drive other than the first
one, you must chain-load GRUB from another boot loader. Refer to the
manual for the boot loader to know how to chain-load GRUB.

Now you can boot GRUB without a GRUB floppy. See the chapter
@ref{Booting} to find out how to boot your operating systems from GRUB.


@node Installing GRUB using grub-install
@section Installing GRUB using grub-install

@strong{Caution:} This procedure is definitely deprecated, because there
are several posibilities that your computer can be unbootable. For
example, most operating systems don't tell GRUB how to map BIOS drives
to OS devices correctly, GRUB merely @dfn{guesses} the mapping. This
will succeed in most cases, but not always. So GRUB provides you with a
user-defined map file called @dfn{device map}, which you must fix, if it
is wrong. @xref{Device map}, for more details.

Unfortunately, if you do want to install GRUB under a UNIX-like OS (such
as @sc{gnu}), invoke the program @command{grub-install} (@pxref{Invoking
grub-install}) as the superuser (@dfn{root}).

The usage is basically very easy. You only need to specify one argument
to the program, namely, where to install GRUB. The argument can be
either of a device file or a GRUB's drive/partition. So, this will
install GRUB into the MBR of the first IDE disk under Linux:

@example
# @kbd{grub-install /dev/hda}
@end example

Likewise, under GNU/Hurd, this has the same effect:

@example
# @kbd{grub-install /dev/hd0}
@end example

If it is the first BIOS drive, this is the same as well:

@example
# @kbd{grub-install '(hd0)'}
@end example

But all the above examples assume that you use GRUB images under
the root directory. If you want GRUB to use images under a directory
other than the root directory, you need to specify the option
@option{--root-directory}. The typical usage is that you create a GRUB
boot floppy with a filesystem. Here is an example:

@example
@group
# @kbd{mke2fs /dev/fd0}
# @kbd{mount -t ext2 /dev/fd0 /mnt}
# @kbd{grub-install --root-directory=/mnt '(fd0)'}
# @kbd{umount /mnt}
@end group
@end example

Another example is in case that you have a separate boot partition
which is mounted at @file{/boot}. Since GRUB is a boot loader, it
doesn't know anything about mountpoints at all. Thus, you need to run
@command{grub-install} like this:

@example
# @kbd{grub-install --root-directory=/boot /dev/hda}
@end example

By the way, as noted above, it is quite difficult to guess BIOS drives
correctly under a UNIX-like OS. Thus, @command{grub-install} will prompt
you to check if it could really guess the correct mappings, after the
installation. The format is defined in @ref{Device map}. Please be
careful enough. If the output is wrong, it is unlikely that your
computer can boot with no problem.

Note that @command{grub-install} is actually just a shell script and the
real task is done by the grub shell @command{grub} (@pxref{Invoking the
grub shell}). Therefore, you may run @command{grub} directly to install
GRUB, without using @command{grub-install}. Don't do that, however,
unless you are very familiar with the internals of GRUB. Installing a
boot loader on a running OS may be extremely dangerous.


@node Booting
@chapter Booting

For Multiboot-compliant kernels, GRUB can load them in a consistent way,
but, for some free operating systems, you need to use some OS-specific
magic.

@menu
* General boot methods::        How to boot OSes with GRUB genenerally
* OS-specific notes::           Notes on some operating systems
@end menu


@node General boot methods
@section How to boot operating systems

GRUB has two distinct boot methods. One of the two is to load an
operating system directly, and the other is to chain-load another boot
loader which then will load an operating system actually. Generally
speaking, the former is desirable, because you don't need to install or
maintain other boot loaders and GRUB is flexible enough to load an
operating system from an arbitrary disk/partition. However, the latter
is sometimes required, since GRUB doesn't support all the existing
operating systems natively.

@menu
* Loading an operating system directly::
* Chain-loading::
@end menu


@node Loading an operating system directly
@subsection How to boot an OS directly with GRUB

Multiboot (@pxref{Top, Multiboot Specification, Motivation, multiboot,
The Multiboot Specification}) is the native format supported by GRUB.
For the sake of convenience, there are also support for Linux, FreeBSD,
NetBSD and OpenBSD. If you want to boot other operating systems, you
will have to chain-load them (@pxref{Chain-loading}).

Generally, GRUB can boot any Multiboot-compliant OS in the following
steps:

@enumerate
@item
Set GRUB's root device to the drive where the OS images are stored by
the command @command{root} (@pxref{root}).

@item
Load the kernel image by the command @command{kernel} (@pxref{kernel}).

@item
If you need modules, load them with the command @command{module}
(@pxref{module}) or @command{modulenounzip} (@pxref{modulenounzip}).

@item
Run the command @command{boot} (@pxref{boot}).
@end enumerate

Linux, FreeBSD, NetBSD and OpenBSD can be booted in a similar
manner. You can load a kernel image by the command @command{kernel} and
then run the command @command{boot}. If the kernel requires some
parameters, just append the parameters to @command{kernel}, after the
file name of the kernel. Also, please refer to @ref{OS-specific notes},
for the information on your OS-specific issues.


@node Chain-loading
@subsection Load another boot loader to boot unsupported operating systems

If you want to boot an unsupported operating system (e.g. Windows 95),
chain-load a boot loader for the operating system. Normally, the boot
loader is embedded in the @dfn{boot sector} of the partition on which
the operating system is installed.

@enumerate
@item
Set GRUB's root device to the partition by the command
@command{rootnoverify} (@pxref{rootnoverify}):

@example
grub> @kbd{rootnoverify (hd0,0)}
@end example

@item
Set the @dfn{active} flag in the partition by the command
@command{makeactive}@footnote{This is not necessary for most of the
modern operating systems.} (@pxref{makeactive}):

@example
grub> @kbd{makeactive}
@end example

@item
Load the boot loader by the command @command{chainloader}
(@pxref{chainloader}):

@example
grub> @kbd{chainloader +1}
@end example

@samp{+1} indicates that GRUB should read one sector from the start of
the partition. The complete description about this syntax can be found
in @ref{Block list syntax}.

@item
Run the command @command{boot} (@pxref{boot}).
@end enumerate

However, DOS and Windows have some deficiencies, so you might have to
use more complicated instructions. @xref{DOS/Windows}, for more
information.


@node OS-specific notes
@section Some caveats on OS-specific issues

Here, we describe some caveats on several operating systems.

@menu
* GNU/Hurd::
* GNU/Linux::
* FreeBSD::
* NetBSD::
* OpenBSD::
* DOS/Windows::