grub.texi

Linux的启动装载(BootLoader)程序

@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::
* SCO UnixWare::
* QNX::
@end menu


@node GNU/Hurd
@subsection GNU/Hurd

Since GNU/Hurd is Multiboot-compliant, it is easy to boot it; there is
nothing special about it. But do not forget that you have to specify a
root partition to the kernel.

@enumerate
@item
Set GRUB's root device to the same drive as GNU/Hurd's. Probably the
command @code{find /boot/gnumach} or similar can help you
(@pxref{find}).

@item
Load the kernel and the module, like this:

@example
@group
grub> @kbd{kernel /boot/gnumach root=hd0s1}
grub> @kbd{module /boot/serverboot}
@end group
@end example

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


@node GNU/Linux
@subsection GNU/Linux

It is relatively easy to boot GNU/Linux from GRUB, because it somewhat
resembles to boot a Multiboot-compliant OS.

@enumerate
@item
Set GRUB's root device to the same drive as GNU/Linux's. Probably the
command @code{find /vmlinuz} or similar can help you (@pxref{find}).

@item
Load the kernel:

@example
grub> @kbd{kernel /vmlinuz root=/dev/hda1}
@end example

If you need to specify some kernel parameters, just append them to the
command. For example, to set @option{vga} to @samp{ext}, do this:

@example
grub> @kbd{kernel /vmlinuz root=/dev/hda1 vga=ext}
@end example

See the documentation in the Linux source tree for complete
information on the available options.

@item
If you use an initrd, execute the command @command{initrd}
(@pxref{initrd}) after @command{kernel}:

@example
grub> @kbd{initrd /initrd}
@end example

@item
Finally, run the command @command{boot} (@pxref{boot}).
@end enumerate

@strong{Caution:} If you use an initrd and specify the @samp{mem=}
option to the kernel to let it use less than actual memory size, you
will also have to specify the same memory size to GRUB. To let GRUB know
the size, run the command @command{uppermem} @emph{before} loading the
kernel. @xref{uppermem}, for more information.


@node FreeBSD
@subsection FreeBSD

GRUB can load the kernel directly, either in ELF or a.out format. But
this is not recommended, since FreeBSD's bootstrap interface sometimes
changes heavily, so GRUB can't guarantee to pass kernel parameters
correctly.

Thus, we'd recommend loading the very flexible loader
@file{/boot/loader} instead. See this example:

@example
@group
grub> @kbd{root (hd0,a)}
grub> @kbd{kernel /boot/loader}
grub> @kbd{boot}
@end group
@end example


@node NetBSD
@subsection NetBSD

GRUB can load NetBSD a.out and ELF directly, follow these steps:

@enumerate
@item
Set GRUB's root device with @command{root} (@pxref{root}).

@item
Load the kernel with @command{kernel} (@pxref{kernel}). You should
append the ugly option @option{--type=netbsd}, if you want to load an
ELF kernel, like this:

@example
grub> @kbd{kernel --type=netbsd /netbsd-elf}
@end example

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

For now, however, GRUB doesn't allow you to pass kernel parameters, so
it may be better to chain-load it instead. For more information, please
see @ref{Chain-loading}.


@node OpenBSD
@subsection OpenBSD

The booting instruction is exactly the same as for NetBSD
(@pxref{NetBSD}).


@node DOS/Windows
@subsection DOS/Windows

GRUB cannot boot DOS or Windows directly, so you must chain-load them
(@pxref{Chain-loading}). However, their boot loaders have some critical
deficiencies, so it may not work to just chain-load them. To overcome
the problems, GRUB provides you with two helper functions.

If you have installed DOS (or Windows) on a non-first hard disk, you
have to use the disk swapping technique, because that OS cannot boot
from any disks but the first one. The workaround used in GRUB is the
command @command{map} (@pxref{map}), like this:

@example
@group
grub> @kbd{map (hd0) (hd1)}
grub> @kbd{map (hd1) (hd0)}
@end group
@end example

This performs a @dfn{virtual} swap between your first and second hard
drive.

@strong{Caution:} This is effective only if DOS (or Windows) uses BIOS
to access the swapped disks. If that OS uses a special driver for the
disks, this probably won't work.

Another problem arises if you installed more than one set of DOS/Windows
onto one disk, because they could be confused if there are more than one
primary partitions for DOS/Windows. Certainly you should avoid doing
this, but there is a solution if you do want to do so. Use the partition
hiding/unhiding technique.

If GRUB @dfn{hide}s a DOS (or Windows) partition (@pxref{hide}), DOS (or
Windows) will ignore the partition. If GRUB @dfn{unhide}s a DOS (or
Windows) partition (@pxref{unhide}), DOS (or Windows) will detect the
partition. Thus, if you have installed DOS (or Windows) on the first
and the second partition of the first hard disk, and you want to boot
the copy on the first partition, do the following:

@example
@group
grub> @kbd{unhide (hd0,0)}
grub> @kbd{hide (hd0,1)}
grub> @kbd{rootnoverify (hd0,0)}
grub> @kbd{chainloader +1}
grub> @kbd{makeactive}
grub> @kbd{boot}
@end group
@end example


@node SCO UnixWare
@subsection SCO UnixWare

It is known that the signature in the boot loader for SCO UnixWare is
wrong, so you will have to specify the option @option{--force} to
@command{chainloader} (@pxref{chainloader}), like this:

@example
@group
grub> @kbd{rootnoverify (hd1,0)}
grub> @kbd{chainloader --force +1}
grub> @kbd{makeactive}
grub> @kbd{boot}
@end group
@end example


@node QNX
@subsection QNX

QNX seems to use a bigger boot loader, so you need to boot it up, like
this:

@example
@group
grub> @kbd{rootnoverify (hd1,1)}
grub> @kbd{chainloader +4}
grub> @kbd{boot}
@end group
@end example


@node Configuration
@chapter Configuration

You've probably noticed that you need to type several commands to boot your
OS. There's a solution to that - GRUB provides a menu interface
(@pxref{Menu interface}) from which you can select an item (using arrow
keys) that will do everything to boot an OS.

To enable the menu, you need a configuration file,
@file{menu.lst} under the boot directory. We'll analyze an example
file.

The file first contains some general settings, the menu interface
related options. You can put these commands (@pxref{Menu-specific
commands}) before any of the items (starting with @command{title}
(@pxref{title})).

@example
@group
#
# Sample boot menu configuration file
#
@end group
@end example

As you may have guessed, these lines are comments. Lines starting with a
hash character (@samp{#}), and blank lines, are ignored by GRUB.

@example
@group
# By default, boot the first entry.
default 0
@end group
@end example

The first entry (here, counting starts with number zero, not one!) will
be the default choice.

@example
@group
# Boot automatically after 30 secs.
timeout 30
@end group
@end example

As the comment says, GRUB will boot automatically in 30 seconds, unless
interrupted with a keypress.

@example
@group
# Fallback to the second entry.
fallback 1
@end group
@end example

If, for any reason, the default entry doesn't work, fall back to the
second one (this is rarely used, for obvious reasons).

Note that the complete descriptions of these commands, which are menu
interface specific, can be found in @ref{Menu-specific
commands}. Other descriptions can be found in @ref{Commands}.

Now, on to the actual OS definitions. You will see that each entry
begins with a special command, @command{title} (@pxref{title}), and the
action is described after it. Note that there is no command
@command{boot} (@pxref{boot}) at the  end of each item. That is because
GRUB automatically executes @command{boot} if it loads other commands
successfully.

The argument for the command @command{title} is used to display a short
title/description of the entry in the menu. Since @command{title}
displays the argument as is, you can write basically anything there.

@example
@group
# For booting GNU/Hurd
title  GNU/Hurd
root   (hd0,0)
kernel /boot/gnumach.gz root=hd0s1
module /boot/serverboot.gz
@end group
@end example

This boots GNU/Hurd from the first hard disk.

@example
@group
# For booting GNU/Linux
title  GNU/Linux
kernel (hd1,0)/vmlinuz root=/dev/hdb1
@end group
@end example

This boots GNU/Linux, but from the second hard disk.

@example
@group
# For booting Mach (getting kernel from floppy)
title  Utah Mach4 multiboot
root   (hd0,2)
pause  Insert the diskette now^G!!
kernel (fd0)/boot/kernel root=hd0s3
module (fd0)/boot/bootstrap
@end group
@end example

This boots Mach with a kernel on a floppy, but the root filesystem at
hd0s3. It also contains a @command{pause} line (@pxref{pause}), which
will cause GRUB to display a prompt and delay, before actually executing
the rest of the commands and booting.

@example
@group
# For booting FreeBSD
title  FreeBSD
root   (hd0,2,a)
kernel /boot/loader
@end group
@end example

This item will boot FreeBSD kernel loaded from the @samp{a} partition of
the third @sc{pc} slice of the first hard disk.

@example
@group
# For booting OS/2
title OS/2
root  (hd0,1)
makeactive
# chainload OS/2 bootloader from the first sector
chainloader +1
# This is similar to "chainload", but loads a specific file
#chainloader /boot/chain.os2
@end group
@end example

This will boot OS/2, using a chain-loader (@pxref{Chain-loading}).