Briefly, a boot loader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to an operating system kernel software (such as the Linux or GNU Hurd kernel). The kernel, in turn, initializes the rest of the operating system (e.g. a GNU system).
GNU GRUB is a very powerful boot loader, which can load a wide variety of free operating systems, as well as proprietary operating systems with chain-loading(1). GRUB is designed to address the complexity of booting a personal computer; both the program and this manual are tightly bound to that computer platform, although porting to other platforms may be addressed in the future.
One of the important features in GRUB is flexibility; GRUB understands filesystems and kernel executable formats, so you can load an arbitrary operating system the way you like, without recording the physical position of your kernel on the disk.
Thus you can load the kernel just by specifying its file name and the drive (and the partition) where the kernel resides. To let GRUB know the drive and the file name, you can either type in them manually via the command-line interface (see section The flexible command-line interface), or use the nice menu interface (see section The simple menu interface) through which you can easily select which OS it boots. To allow you to customize the menu, GRUB will load a preexisting configuration file (see section Configuration). Note that you can not only enter the command-line interface whenever you like, but also you can edit specific menu entries prior to using them.
In the following chapters, you will learn how to specify a drive or a partition, and a file name (see section Naming convention) to GRUB, how to install GRUB on your drive (see section Installation), and how to boot your OSes (see section Booting), step by step.
GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU Hurd with the University of Utah's Mach 4 microkernel (now known as GNU Mach). Erich and Brian Ford designed the Multiboot Specification (see section `Motivation' in The Multiboot Specification), because they were determined not to add to the large number of mutually-incompatible PC boot methods.
Erich then began modifying the FreeBSD boot loader so that it would understand Multiboot. He soon realized that it would be a lot easier to write his own boot loader from scratch than to keep working on the FreeBSD boot loader, and so GRUB was born.
Erich added many features to GRUB, but other priorities prevented him from keeping up with the demands of its quickly-expanding user base. In 1999, Gordon Matzigkeit and OKUJI Yoshinori adopted GRUB as an official GNU package, and opened its development by making the latest sources available via anonymous CVS. See section How to obtain and build GRUB, for more information.
The primary requirement for GRUB is that it be compliant with the Multiboot Specification, which is described in section `Motivation' in The Multiboot Specification.
The other goals, listed in approximate order of importance, are:
Except for specific compatibility modes (chain-loading and the Linux piggyback format), all kernels will be started in much the same state as in the Multiboot Specification. Only kernels loaded at 1 megabyte or above are presently supported. Any attempt to load below that boundary will simply result in immediate failure and an error message reporting the problem.
In addition to the requirements above, GRUB has the following features (note that the Multiboot Specification doesn't require all the features that GRUB supports):
The following is a quotation from Gordon Matzigkeit, a GRUB fanatic:
Some people like to acknowledge both the operating system and kernel when they talk about their computers, so they might say they use "GNU/Linux" or "GNU/Hurd". Other people seem to think that the kernel is the most important part of the system, so they like to call their GNU operating systems "Linux systems."
I, personally, believe that this is a grave injustice, because the boot loader is the most important software of all. I used to refer to the above systems as either "LILO"(3) or "GRUB" systems.
Unfortunately, nobody ever understood what I was talking about; now I just use the word "GNU" as a pseudonym for GRUB.
So, if you ever hear people talking about their alleged "GNU" systems, remember that they are actually paying homage to the best boot loader around... GRUB!
We, the GRUB maintainers, do not (usually) encourage Gordon's level of fanaticism, but it helps to remember that boot loaders deserve recognition. We hope that you enjoy using GNU GRUB as much as we did writing it.
The device syntax used in GRUB is a wee bit different from what you may have seen before in your operating system(s), and you need to know it so that you can specify a drive/partition.
Look at the following examples and explanations:
(fd0)
First of all, GRUB requires that the device name is enclosed with `(' and `)'. The `fd' part means that it is a floppy disk. The number `0' is the drive number, which is counted from zero. This expression means that GRUB will use the whole floppy disk.
(hd0,1)
Here, `hd' means it is a hard disk drive. The first integer `0' indicates the drive number, that is, the first hard disk, while the second integer, `1', indicates the partition number (or the PC slice number in the BSD terminology). Once again, please note that the partition numbers are counted from 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.
(hd0,4)
This specifies the first extended partition of the first hard disk drive. Note that the partition numbers for extended partitions are counted from `4', regardless of the actual number of primary partitions on your hard disk.
(hd1,a)
This means the BSD `a' partition of the second hard disk. If you need to specify which PC slice number should be used, use something like this: `(hd1,0,a)'. If the PC slice number is omitted, GRUB searches for the first PC slice which has a BSD `a' partition.
Of course, to actually access the disks or partitions with GRUB, you need to use the device specification in a command, like `root (fd0)' or `unhide (hd0,2)'. To help you find out which number is a partition you want, the GRUB command-line (see section The flexible command-line interface) options have argument completion. That means that, for example, you only need to type `root (', followed by a 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 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:
(hd0,0)/vmlinuz
This specifies the file named `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.
First, you need to have GRUB itself properly installed on your system, (see section How to obtain and build 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} (see section 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 `/usr/share/grub/i386-pc'. You need to copy the files `stage1', `stage2', and `*stage1_5' to the directory `/boot/grub'. Here the directory where GRUB images are installed and the directory where GRUB will use to find them are called image directory and boot directory, respectively.
To create a GRUB boot floppy, you need to take the files `stage1' and `stage2' from the image directory, and write them to the first and the second block of the floppy disk, respectively.
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:
# cd /usr/share/grub/i386-pc # dd if=stage1 of=/dev/fd0 bs=512 count=1 1+0 records in 1+0 records out # dd if=stage2 of=/dev/fd0 bs=512 seek=1 153+1 records in 153+1 records out #
The device file name may be different. Consult the manual for your OS.
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 `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 section Installing GRUB using grub-install, for more details.
Once started, GRUB will show the command-line interface (see section The flexible command-line interface). First, set the GRUB's root device(4).} to the boot directory, like this:
grub> root (hd0,0)
If you are not sure which partition actually holds these files, use the command @command{find} (see section find), like this:
grub> find /boot/grub/stage1
This will search for the file name `/boot/grub/stage1' and show the devices which contain the file.
Once you've set the root device correctly, run the command @command{setup} (see section setup):
grub> setup (hd0)
This command will install GRUB on the MBR in the first drive. If you want to install GRUB into the boot sector of a partition instead of the MBR, specify a partition into which you want to install GRUB:
grub> setup (hd0,0)
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 section Booting to find out how to boot your operating systems from GRUB.
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 guesses the mapping. This will succeed in most cases, but not always. So GRUB provides you with a user-defined map file called device map, which you must fix, if it is wrong. See section The map between BIOS drives and OS devices, for more details.
Unfortunately, if you do want to install GRUB under a UNIX-like OS (such as GNU), invoke the program @command{grub-install} (see section Invoking grub-install) as the superuser (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:
# grub-install /dev/hda
Likewise, under Hurd, this has the same effect:
# grub-install /dev/hd0
If it is the first BIOS drive, this is the same as well:
# grub-install '(hd0)'
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:
# mke2fs /dev/fd0 # mount -t ext2 /dev/fd0 /mnt # grub-install --root-directory=/mnt '(fd0)' # umount /mnt
Another example is in case that you have a separate boot partition which is mounted at `/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:
# grub-install --root-directory=/boot /dev/hda
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 section The map between BIOS drives and OS devices. 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} (see section 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.
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.
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.
Multiboot (see section `Motivation' in 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 (see section Load another boot loader to boot unsupported operating systems).
Generally, GRUB can boot any Multiboot-compliant OS in the following steps:
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 section Some caveats on OS-specific issues, for the information on your OS-specific issues.
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 boot sector of the partition on which the operating system is installed.
grub> rootnoverify (hd0,0)
grub> makeactive
grub> chainloader +1`+1' indicates that GRUB should read one sector from the start of the partition. The complete description about this syntax can be found in section How to specify block lists.
However, DOS and Windows have some deficiencies, so you might have to use more complicated instructions. See section DOS/Windows, for more information.
Here, we describe some caveats on several operating systems.
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.
find /boot/gnumach or similar can help you
(see section find).
grub> kernel /boot/gnumach root=hd0s1 grub> module /boot/serverboot
It is relatively easy to boot GNU/Linux from GRUB, because it somewhat resembles to boot a Multiboot-compliant OS.
find /vmlinuz or similar can help you (see section find).
grub> kernel /vmlinuz root=/dev/hda1If you need to specify some kernel parameters, just append them to the command. For example, to set @option{vga} to `ext', do this:
grub> kernel /vmlinuz root=/dev/hda1 vga=extSee the documentation in the Linux source tree for the complete information on the available options.
grub> initrd /initrd
Caution: If you use an initrd and specify the `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} before loading the kernel. See section uppermem, for more information.
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 `/boot/loader' instead. See this example:
grub> root (hd0,a) grub> kernel /boot/loader grub> boot
GRUB can load NetBSD a.out and ELF directly, follow these steps:
grub> kernel --type=netbsd /netbsd-elf
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 section Load another boot loader to boot unsupported operating systems.
The booting instruction is exactly the same as for NetBSD (see section NetBSD).
GRUB cannot boot DOS or Windows directly, so you must chain-load them (see section Load another boot loader to boot unsupported operating systems). 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} (see section map), like this:
grub> map (hd0) (hd1) grub> map (hd1) (hd0)
This performs a virtual swap between your first and second hard drive.
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 hides a DOS (or Windows) partition (see section hide), DOS (or Windows) will ignore the partition. If GRUB unhides a DOS (or Windows) partition (see section 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:
grub> unhide (hd0,0) grub> hide (hd0,1) grub> rootnoverify (hd0,0) grub> chainloader +1 grub> makeactive grub> boot
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} (see section chainloader), like this:
grub> rootnoverify (hd1,0) grub> chainloader --force +1 grub> makeactive grub> boot
You probably noticed that you need to type several commands to boot your OS. There's a solution to that - GRUB provides a menu interface (see section The simple 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, `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 (see section The list of commands for the menu only) before any of the items (starting with @command{title} (see section title)).
# # Sample boot menu configuration file #
As you may have guessed, these lines are comments. Lines starting with a hash character (`#'), and blank lines, are ignored by GRUB.
# By default, boot the first entry. default 0
The first entry (here, counting starts with number zero, not one!) will be the default choice.
# Boot automatically after 30 secs. timeout 30
As the comment says, GRUB will boot automatically in 30 seconds, unless interrupted with a keypress.
# Fallback to the second entry. fallback 1
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 section The list of commands for the menu only. Other descriptions can be found in section The list of available commands.
Now, on to the actual OS definitions. You will see that each entry begins with a special command, @command{title} (see section title), and the action is described after it. Note that there is no command @command{boot} (see section 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 in there.
# For booting the GNU Hurd title GNU/Hurd root (hd0,0) kernel /boot/gnumach.gz root=hd0s1 module /boot/serverboot.gz
This boots GNU/Hurd from the first hard disk.
# For booting Linux title GNU/Linux kernel (hd1,0)/vmlinuz root=/dev/hdb1
This boots GNU/Linux, but from the second hard disk.
# 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
This boots Mach with a kernel on a floppy, but the root filesystem at hd0s3. It also contains a @command{pause} line (see section pause), which will cause GRUB to display a prompt and delay, before actually executing the rest of the commands and booting.
# For booting FreeBSD title FreeBSD root (hd0,2,a) kernel /boot/loader
This item will boot FreeBSD kernel loaded from the `a' partition of the third PC slice of the first hard disk.
# 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
This will boot OS/2, using a chain-loader (see section Load another boot loader to boot unsupported operating systems).
# For booting Windows NT or Windows95 title Windows NT / Windows 95 boot menu root (hd0,0) makeactive chainloader +1 # For loading DOS if Windows NT is installed # chainload /bootsect.dos
The same as the above, but for Windows.
# For installing GRUB into the hard disk title Install GRUB into the hard disk root (hd0,0) setup (hd0)
This will just (re)install GRUB onto the hard disk.
# Change the colors. title Change the colors color light-green/brown blink-red/blue
In the last entry, the command @command{color} is used (see section color), to change the menu colors (try it!). This command is somewhat special, because it can be used both in the command-line and in the menu. GRUB has several such commands, see section The list of general commands.
We hope that you now understand how to use the basic features of GRUB. To learn more about GRUB, see the following chapters.
Although GRUB is a disk-based boot loader, it does provide network support. To use the network support, you need to enable at least one network driver in the GRUB build process. For more information please see `netboot/README.netboot' in the source distribution.
GRUB requires a file server and optionally a server that will assign an IP address to the machine on which GRUB is running. For the former, only TFTP is supported at the moment. The latter is either BOOTP, DHCP or a RARP server(6). It is not necessary to run both the servers on one computer. How to configure these servers is beyond the scope of this document, so please refer to the manuals specific to those protocols/servers.
If you decided to use a server to assign an IP address, set up the server and run @command{bootp} (see section bootp), @command{dhcp} (see section dhcp) or @command{rarp} (see section rarp) for BOOTP, DHCP or RARP, respectively. Each command will show an assigned IP address, a netmask, an IP address for your TFTP server and a gateway. If any of the addresses is wrong or it causes an error, probably the configuration of your servers isn't set up properly.
Otherwise, run @command{ifconfig}, like this:
grub> ifconfig --address=192.168.110.23 --server=192.168.110.14
You can also use @command{ifconfig} in conjugation with @command{bootp}, @command{dhcp} or @command{rarp} (e.g. to reassign the server address manually). See section ifconfig, for more details.
Finally, download your OS images from your network. The network can be accessed using the network drive `(nd)'. Everything else is very similar to the normal instructions (see section Booting).
Here is an example:
grub> bootp Probing... [NE*000] NE2000 base ... Address: 192.168.110.23 Netmask: 255.255.255.0 Server: 192.168.110.14 Gateway: 192.168.110.1 grub> root (nd) grub> kernel /tftproot/gnumach.gz root=sd0s1 grub> module /tftproot/serverboot.gz grub> boot
It is sometimes very useful to boot from a network, especially, when you use a machine which has no local disk. In this case, you need to obtain a kind of Net Boot ROM, such as a PXE ROM or a free software package like Etherboot. Such a Boot ROM first boots the machine, sets up the network card installed into the machine, and downloads a second stage boot image from the network. Then, the second image will try to boot an operating system from the network actually.
GRUB provides two second stage images, `nbgrub' and `pxegrub' (see section GRUB image files). Those images are the same as the normal Stage 2, except that they set up a network automatically, and try to load a configuration file from the network, if specified. The usage is very simple: If the machine has a PXE ROM, use `pxegrub'. If the machine has a NBI loader such as Etherboot, use `nbgrub'. There is no difference between them but their formats. As how to load a second stage image you want to use should be described in the manual on your Net Boot ROM, please refer to the manual, for more information.
However, there is one thing specific to GRUB. Namely, how to specify a configuration file in a BOOTP/DHCP server. For now, GRUB uses the tag `150', to get the name of a configuration file. This below is an example about a BOOTP configuration:
.allhost:hd=/tmp:bf=null:\
:ds=145.71.35.1 145.71.32.1:\
:sm=255.255.254.0:\
:gw=145.71.35.1:\
:sa=145.71.35.5:
foo:ht=1:ha=63655d0334a7:ip=145.71.35.127:\
:bf=/nbgrub:\
:tc=.allhost:\
:T150="/tftpboot/menu.lst.foo":
See the manual about your BOOTP/DHCP server, for more information. The exact syntax should differ from the example, more or less.
This chapter describes how to use the serial terminal support in GRUB.
If you have many computers or computers with no display/keyboard, it would be very useful to control the computers with serial communications. To connect a computer with another via a serial line, you need to prepare a null-modem (cross) serial cable, and you may need to have multiport serial boards, if your computer doesn't have extra serial ports. In addition, a terminal emulator is also required, such as minicom. Refer to a manual of your operating system, for more information.
As for GRUB, the instruction to set up a serial terminal is quite simple. First of all, make sure that you haven't specified the option @option{--disable-serial} to the configure script when you built your GRUB images. If you get them in binary form, probably they have serial terminal support already.
Then, initialize your serial terminal after GRUB starts up. Here is an example:
grub> serial --unit=0 --speed=9600 grub> terminal serial
The command @command{serial} initializes the serial unit 0 with the speed 9600bps. The serial unit 0 is usually called `COM1', so, if you want to use COM2, you must specify `--unit=1' instead. This command accepts many other options, so please refer to section serial, for more details.
The command @command{terminal} (see section terminal) chooses which type of
terminal you want to use. In that case above, the terminal will be a
serial terminal, but you can also pass console to the command,
like `terminal serial console'. In this case, a terminal in which
you press any key will be selected as a GRUB terminal.
However, note that GRUB assumes that your terminal emulator is compatible with VT100 by default. This is true for most terminal emulators nowadays, but you should pass the option @option{--dumb} to the command, if your terminal emulator is not VT100-compatible or implements few VT100 escape sequences. If you specify the option, then GRUB doesn't provide you with the menu interface, because the menu requires several fancy features for your terminal. Instead, GRUB only gives you the hidden menu interface and the command-line interface (see section GRUB's user interface).
You may be interested in how to prevent ordinary users from doing whatever they like, if you share your computer with other people. So this chapter describes how to improve the security of GRUB.
One thing which could be a security hole is that the user can do too many things with GRUB, because GRUB allows to modify its configuration and run arbitrary commands at run-time. For example, the user can read even `/etc/passwd' in the command-line interface by the command @command{cat} (see section cat). So it is necessary to disable all the interactive operations.
Thus, GRUB provides password feature, so that only administrators can start the interactive operations (i.e. editing menu entries and entering the command-line interface). To use this feature, you need to run the command @command{password} in your configuration file (see section password), like this:
password --md5 PASSWORD
If this is specified, GRUB disallows any interactive control, until you press the key p and enter a correct password. The option @option{--md5} tells GRUB that `PASSWORD' is in MD5 format. If it is omitted, GRUB assumes the `PASSWORD' is in clear text.
You can encrypt your password with the command @command{md5crypt} (see section md5crypt). For example, run the grub shell (see section Invoking the grub shell), and enter your password:
grub> md5crypt Password: ********** Encrypted: $1$U$JK7xFegdxWH6VuppCUSIb.
Then, cut and paste the encrypted password to your configuration file.
Also, you can specify an optional argument to @command{password}. See this example:
password PASSWORD /boot/grub/menu-admin.lst
In this case, GRUB will load `/boot/grub/menu-admin.lst' as a configuration file when you enter the valid password.
Another thing which may be dangerous is that any user can choose any menu entry. Usually, this wouldn't be problematic, but you might want to permit only administrators to run some of your menu entries, such as an entry for booting an insecure OS like DOS.
GRUB provides the command @command{lock} (see section lock). This command always fails until you enter a valid password, so you can use it, like this:
title Boot DOS lock rootnoverify (hd0,1) makeactive chainload +1
You should insert @command{lock} right after @command{title}, because any user can execute commands in an entry, until GRUB encounters @command{lock}.
You can also use the command @command{password} instead of @command{lock}. In this case the boot process will ask for the password and stop if it was entered incorrectly. Since the @command{password} takes its own PASSWORD argument this is useful if you want different passwords for different entries.
GRUB consists of several images: two essential stages, optional stages called Stage 1.5, and two network boot images. Here is a short overview of them. See section Hacking GRUB, for more details.
GRUB uses a special syntax for specifying disk drives which can be accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish between IDE, ESDI, SCSI, or others. You must know yourself which BIOS device is equivalent to which OS device. Normally, that will be clear if you see the files in a device or use the command @command{find} (see section find).
The device syntax is like this:
(device[,part-num][,bsd-subpart-letter])
`[]' means the parameter is optional. device should be either `fd' or `hd' followed by a digit, like `fd0'. But you can also set device to a hexadecimal or a decimal, which is a BIOS drive number, so the following are equivalent:
(hd0) (0x80) (128)
part-num represents the partition number of device, starting from zero for primary partitions and from four for extended partitions, and bsd-subpart-letter represents the BSD disklabel subpartition, such as `a' or `e'.
A shortcut for specifying BSD subpartitions is
(device,bsd-subpart-letter), in this case, GRUB
searches for the first PC partition containing a BSD disklabel, then
finds the subpartition bsd-subpart-letter. Here is an example:
(hd0,a)
The syntax like `(hd0)' represents using the entire disk (or the MBR when installing GRUB), while the syntax like `(hd0,0)' represents using the partition of the disk (or the boot sector of the partition when installing GRUB).
If you enabled the network support, the special drive, `(nd)', is also available. Before using the network drive, you must initialize the network. See section Downloading OS images from a network, for more information.
There are two ways to specify files, by absolute file name and by block list.
An absolute file name resembles a Unix absolute file name, using
`/' for the directory separator (not `\' as in DOS). One
example is `(hd0,0)/boot/grub/menu.lst'. This means the file
`/boot/grub/menu.lst' in the first partition of the first hard
disk. If you omit the device name in an absolute file name, GRUB uses
GRUB's root device implicitly. So if you set the root device to,
say, `(hd1,0)' by the command @command{root} (see section root), then
/boot/kernel is the same as (hd1,0)/boot/kernel.
A block list is used for specifying a file that doesn't appear in the
filesystem, like a chainloader. The syntax is
[offset]+length[,[offset]+length]....
Here is an example:
0+100,200+1,300+300
This represents that GRUB should read blocks 0 through 99, block 200, and blocks 300 through 599. If you omit an offset, then GRUB assumes the offset is zero.
Like the file name syntax (see section How to specify files), if a blocklist
does not contain a device name, then GRUB uses GRUB's root
device. So (hd0,1)+1 is the same as +1 when the root
device is `(hd0,1)'.
GRUB has both a simple menu interface for choosing preset entries from a configuration file, and a highly flexible command-line for performing any desired combination of boot commands.
GRUB looks for its configuration file as soon as it is loaded. If one is found, then the full menu interface is activated using whatever entries were found in the file. If you choose the command-line menu option, or if the configuration file was not found, then GRUB drops to the command-line interface.
The command-line interface provides a prompt and after it an editable text area much like a command-line in Unix or DOS. Each command is immediately executed after it is entered(7). The commands (see section The list of command-line and menu entry commands) are a subset of those available in the configuration file, used with exactly the same syntax.
Cursor movement and editing of the text on the line can be done via a subset of the functions available in the Bash shell:
When typing commands interactively, if the cursor is within or before the first word in the command-line, pressing the TAB key (or C-i) will display a listing of the available commands, and if the cursor is after the first word, the TAB will provide a completion listing of disks, partitions, and file names depending on the context.
Note that you cannot use the completion functionality in the TFTP filesystem. This is because TFTP doesn't support file name listing for the security.
The menu interface is quite easy to use. Its commands are both reasonably intuitive and described on screen.
Basically, the menu interface provides a list of boot entries to the user to choose from. Use the arrow keys to select the entry of choice, then press RET to run it. An optional timeout is available to boot the default entry (the first one if not set), which is aborted by pressing any key.
Commands are available to enter a bare command-line by pressing c (which operates exactly like the non-config-file version of GRUB, but allows one to return to the menu if desired by pressing ESC) or to edit any of the boot entries by pressing e.
If you protect the menu interface with a password (see section Protecting your computer from cracking), all you can do is choose an entry by pressing RET, or press p to enter the password.
The menu entry editor looks much like the main menu interface, but the lines in the menu are individual commands in the selected entry instead of entry names.
If an ESC is pressed in the editor, it aborts all the changes made to the configuration entry and returns to the main menu interface.
When a particular line is selected, the editor places the user at a special version of the GRUB command-line to edit that line. When the user hits RET, GRUB replaces the line in question in the boot entry with the changes (unless it was aborted via ESC, in which case the changes are thrown away).
If you want to add a new line to the menu entry, press o if adding a line after the current line or press O if before the current line.
To delete a line, hit the key d. Although GRUB does not support undo unfortunately, you can do almost the same thing by just returning to the main menu.
When your terminal is dumb or you request GRUB of hiding the menu interface explicitly with the command @command{hiddenmenu} (see section hiddenmenu), GRUB doesn't show the menu interface (see section The simple menu interface) and automatically boots the default entry, unless interrupted by pressing ESC.
When you interrupt the timeout and your terminal is dumb, GRUB falls back to the command-line interface (see section The flexible command-line interface).
In this chapter, we list all commands that are available in GRUB.
Commands belong to different groups. A few can only be used in the global section of the configuration file (or "menu"); most of them can be entered on the command-line and can be either used in the menu or in the menu entries.
The semantics used in parsing the configuration file are the following:
These commands can only be used in the menu:
You can specify `saved' instead of a number. In this case, the default entry is the entry saved with the command @command{savedefault}. See section savedefault, for more information.
default
command (see section default)). This obviously won't help if the machine was
rebooted by a kernel that GRUB loaded.
Commands usable both in the menu and in the command-line.
If you specify @option{--with-configfile} to this command, GRUB will fetch and load a configuration file specified by your BOOTP server with the vendor tag `150'.
foreground/background. foreground and
background are symbolic color names. A symbolic color name must be
one of these:
But only the first eight names can be used for background. You can
prefix blink- to foreground if you want a blinking
foreground color.
This command can be used in the configuration file and on the command line, so you may write something like this in your configuration file:
# Set default colors. color light-gray/blue black/light-gray # Change the colors. title OS-BS like color magenta/blue black/magenta
grub> device (fd0) /floppy-image grub> device (hd0) /dev/sd0
This command can be used only in the grub shell (see section Invoking the grub shell).
If you specify @option{--with-configfile} to this command, GRUB will fetch and load a configuration file specified by your DHCP server with the vendor tag `150'.
0-0xff; from and
to are the starting and ending sectors, expressed as an absolute
sector number.
The serial port is not used as a communication channel unless the @command{terminal} command is used (see section terminal).
This command is only available if GRUB is compiled with serial support. See also section Using GRUB via a serial line.
grub> setkey capslock control grub> setkey control capslock
A key must be an alphabet, a digit, or one of these symbols: `escape', `exclam', `at', `numbersign', `dollar', `percent', `caret', `ampersand', `asterisk', `parenleft', `parenright', `minus', `underscore', `equal', `plus', `backspace', `tab', `bracketleft', `braceleft', `bracketright', `braceright', `enter', `control', `semicolon', `colon', `quote', `doublequote', `backquote', `tilde', `shift', `backslash', `bar', `comma', `less', `period', `greater', `slash', `question', `alt', `space', `capslock', `FX' (`X' is a digit), and `delete'. This table describes to which character each of the symbols corresponds:
This may not make sense for most users, but GRUB supports Hercules console as well. Hercules console is usable like the ordinary console, and the usage is quite similar to that for serial terminals: specify @option{hercules} as the argument.
Override a TFTP server address returned by a BOOTP/DHCP/RARP server. The argument ipaddr must be in dotted decimal format, like `192.168.0.15'. This command is only available if GRUB is compiled with netboot support. See also section Downloading OS images from a network.
These commands are usable in the command-line and in menu entries. If you forget a command, you can run the command @command{help} (see section help).
grub> cat /etc/fstab
Differ in size: 0x1234 [foo], 0x4321 [bar]
If the sizes are equal but the bytes at an offset differ, then print the bytes like this:
Differ at the offset 777: 0xbe [foo], 0xef [bar]
If they are completely identical, nothing will be printed.
Usually, you don't need to run this command directly. See section setup.
/boot/grub/stage1.
In short, it will perform a full install presuming the Stage 2 or Stage 1.5(9) is in its final install location.
In slightly more detail, it will load stage1_file, validate that it is a GRUB Stage 1 of the right version number, install a blocklist for loading stage2_file as a Stage 2. If the option @option{d} is present, the Stage 1 will always look for the actual disk stage2_file was installed on, rather than using the booting drive. The Stage 2 will be loaded at address addr, which must be `0x8000' for a true Stage 2, and `0x2000' for a Stage 1.5. If addr is not present, GRUB will determine the address automatically. It then writes the completed Stage 1 to the first block of the device dest_dev. If the options @option{p} or config_file are present, then it reads the first block of stage2, modifies it with the values of the partition stage2_file was found on (for @option{p}) or places the string config_file into the area telling the stage2 where to look for a configuration file at boot time. Likewise, if real_config_file is present and stage2_file is a Stage 1.5, then the Stage 2 config_file is patched with the configuration file name real_config_file. This command preserves the DOS BPB (and for hard disks, the partition table) of the sector the Stage 1 is to be installed into.
Caution: Several buggy BIOSes don't pass a booting drive properly when booting from a hard disk drive. Therefore, you will have to specify the option @option{d}, whether your Stage2 resides at the booting drive or not, if you have such a BIOS unfortunately. We know these are defective in that:
Caution2: A number of BIOSes don't return a correct LBA support bitmap even if they do have the support. So GRUB provides a solution to ignore the wrong bitmap, that is, the option @option{--force-lba}. Don't use this option if you know that your BIOS doesn't have LBA support.
Caution3: You must specify the option @option{--stage2} in the grub shell, if you cannot unmount the filesystem where your stage2 file resides. The argument should be the file name in your operating system.
This command also accepts the option @option{--type} so that you can specify the kernel type of file explicitly. The argument type must be one of these: `netbsd', `freebsd', `openbsd', `linux', `biglinux', and `multiboot'. However, you need to specify it only if you want to load a NetBSD ELF kernel, because GRUB can automatically determine a kernel type in the other cases, quite safely.
The option @option{--no-mem-option} is effective only for Linux. If the option is specified, GRUB doesn't pass the option @option{mem=} to the kernel.
This command is used in a menu, as shown in this example:
title This entry is too dangerous to be executed by normal users lock root (hd0,a) kernel /no-security-os
See also section Protecting your computer from cracking.
grub> map (hd0) (hd1) grub> map (hd1) (hd0)
The example exchanges the order between the first hard disk and the second hard disk. See also section DOS/Windows.
ES:ESI, used by some chain-loaded boot loaders), the
BSD drive-type (for booting BSD kernels using their native boot format),
and correctly determine the PC partition where a BSD sub-partition is
located. The optional hdbias parameter is a number to tell a BSD
kernel how many BIOS drive numbers are on controllers before the current
one. For example, if there is an IDE disk and a SCSI disk, and your
FreeBSD root partition is on the SCSI disk, then use a `1' for
hdbias.
See also section rootnoverify.
default saved timeout 10 title GNU/Linux root (hd0,0) kernel /boot/vmlinuz root=/dev/sda1 vga=ext initrd /boot/initrd savedefault title FreeBSD root (hd0,a) kernel /boot/loader savedefault
With this configuration, GRUB will choose the entry booted previously as the default entry. See also section default.
The option @option{--prefix} specifies the directory under which GRUB images are put. If it is not specified, GRUB automatically searches them in `/boot/grub' and `/grub'.
The options @option{--force-lba} and @option{--stage2} are just passed to @command{install} if specified. See section install, for more information.
Caution: This should be used with great caution, and should only be necessary on some old machines. GRUB's BIOS probe can pick up all RAM on all new machines the author has ever heard of. It can also be used for debugging purposes to lie to an OS.
This chapter describes error messages reported by GRUB when you encounter trouble. See section Invoking the grub shell, if your problem is specific to the grub shell.
The general way that the Stage 1 handles errors is to print an error string and then halt. Pressing CTRL-ALT-DEL will reboot.
The following is a comprehensive list of error messages for the Stage 1:
The general way that the Stage 1.5 handles errors is to print an error
number in the form Error num and then halt. Pressing
CTRL-ALT-DEL will reboot.
The error numbers correspond to the errors reported by Stage 2. See section Errors reported by the Stage 2.
The general way that the Stage 2 handles errors is to abort the operation in question, print an error string, then (if possible) either continue based on the fact that an error occurred or wait for the user to deal with the error.
The following is a comprehensive list of error messages for the Stage 2 (error numbers for the Stage 1.5 are listed before the colon in each description):
This chapter documents the grub shell @command{grub}. Note that the grub shell is an emulator; it doesn't run under the native environment, so it sometimes does something wrong. Therefore, you shouldn't trust it too much. If there is anything wrong with it, don't hesitate to try the native GRUB environment, especially when it guesses a wrong map between BIOS drives and OS devices.
You can use the command @command{grub} for installing GRUB under your operating systems and for a testbed when you add a new feature into GRUB or when fix a bug. @command{grub} is almost the same as the Stage 2, and, in fact, it shares the source code with the Stage 2 and you can use the same commands (see section The list of available commands) in @command{grub}. It is emulated by replacing BIOS calls with UNIX system calls and libc functions.
The command @command{grub} accepts the following options:
The installation procedure is the same as under the native Stage 2. See section Installation, for more information. The command @command{grub}-specific information is described here.
What you should be careful about is buffer cache. @command{grub} makes use of raw devices instead of filesystems that your operating systems serve, so there exists a potential problem that some cache inconsistency may corrupt your filesystems. What we recommend is:
In addition, enter the command @command{quit} when you finish the installation. That is very important because @command{quit} makes the buffer cache consistent. Do not push C-c.
If you want to install GRUB non-interactively, specify `--batch' option in the command-line. This is a simple example:
#!/bin/sh # Use /usr/sbin/grub if you are on an older system. /sbin/grub --batch <<EOT 1>/dev/null 2>/dev/null root (hd0,0) setup (hd0) quit EOT
When you specify the option @option{--device-map} (see section Introduction into the grub shell), the grub shell creates the device map file automatically unless it already exists. The file name `/boot/grub/device.map' is preferred.
If the device map file exists, the grub shell reads it to map BIOS drives to OS devices. This file consists of lines like this:
device file
device is a drive, which syntax is the same as the one in GRUB (see section How to specify devices), and file is an OS's file, which is normally a device file.
The reason why the grub shell gives you the device map file is that it cannot guess the map between BIOS drives and OS devices correctly in some environments. For example, if you exchange the boot sequence between IDE and SCSI in your BIOS, it mistakes the order.
Thus, edit the file if the grub shell makes a mistake. You can put any comments in the file if needed, as the grub shell assumes that a line is just a comment if the first character is `#'.
The program @command{grub-install} installs GRUB on your drive by the grub shell (see section Invoking the grub shell). You must specify the device name on which you want to install GRUB, like this:
grub-install install_device
The device name install_device is an OS device name or a GRUB device name.
@command{grub-install} accepts the following options:
grub-install --root-directory=/boot '(hd0)'
grub-install --grub-shell="grub --read-only" /dev/fd0
The program @command{grub-md5-crypt} encrypts a password in MD5 format. This is just a frontend of the grub shell (see section Invoking the grub shell). Passwords encrypted by this program can be used with the command @command{password} (see section password).
@command{grub-md5-crypt} accepts the following options:
The program @command{mbchk} checks for the format of a Multiboot kernel. We recommend using this program before booting your own kernel by GRUB.
@command{mbchk} accepts the following options:
$ mke2fs /dev/fd0
$ /sbin/grub --batch <<EOT root (fd0) setup (fd0) quit EOT
ld -vThis will show two versions, but only the latter is important. If the version is identical with what you have installed, the installation was not bad. Well, please try:
gcc -Wl,-v 2>&1 | grep "GNU ld"If this is not identical with the result above, you should specify the directory where you have installed binutils for the script configure, like this:
./configure --with-binutils=/usr/local/binIf you follow the instructions above but GRUB still crashes, probably there is a serious bug in GRUB. See section Reporting bugs.
grub> kernel /vmlinuz mem=128MYou may pass other options in the same way. See See section GNU/Linux, for more details.
grub> root (hd0,1) grub> install /grub/stage1 d (hd0) /grub/stage2 p /grub/menu.lst
FDISK /MBR on Windows. If you want to install LILO(10), run
/sbin/lilo on GNU/Linux.
Caution: GRUB requires binutils-2.9.1.0.23 or later because the GNU assembler has been changed so that it can produce real 16bits machine code between 2.9.1 and 2.9.1.0.x. See http://sourceware.cygnus.com/binutils/, to obtain information on how to get the latest version.
GRUB is available from the GNU alpha archive site ftp://alpha.gnu.org/gnu/grub or any of its mirrors. The file will be named grub-version.tar.gz. The current version is 0.90, so the file you should grab is:
ftp://alpha.gnu.org/gnu/grub/grub-0.90.tar.gz
To unbundle GRUB use the instruction:
zcat grub-0.90.tar.gz | tar xvf -
which will create a directory called `grub-0.90' with all the sources. You can look at the file `INSTALL' for detailed instructions on how to build and install GRUB, but you should be able to just do:
cd grub-0.90 ./configure make install
This will install the grub shell `grub' (see section Invoking the grub shell), the Multiboot checker `mbchk' (see section Invoking mbchk), and the GRUB images. This will also install the GRUB manual.
Also, the latest version is available from the CVS. The repository is:
:pserver:[email protected]:/cvsroot/grub
and the module is:
grub
The password for anoncvs is empty. So the instruction is:
cvs -d :pserver:[email protected]:/cvsroot/grub login Password: ENTER cvs -d :pserver:[email protected]:/cvsroot/grub co grub
This is the guideline of how to report bugs. Take a look at this list below before you send e-mail to [email protected]:
If you realize the guideline above, send e-mail to [email protected], and we will try to fix the bugs.
Here are some ideas that might happen in the future:
See the file `TODO' in the source distribution, for more information.
This chapter documents the user-invisible aspect of GRUB.
As a general rule of software development, it is impossible to keep the descriptions of the internals up-to-date, and it is quite hard to document everything. So refer to the source code, whenever you are not satisfied with this documentation. Please assume that this gives just hints to you.
GRUB consists of two distinct components, called stages, which are loaded at different times in the boot process. Because they run mutual-exclusively, sometimes a memory area overlaps with another memory area. And, even in one stage, a single memory area can be used for various purposes, because their usages are mutually exclusive.
Here is the memory map of the various components:
See the file `stage2/shared.h', for more information.
Stage 1 and Stage 2 have embedded variables whose locations are well-defined, so that the installation can patch the binary file directly without recompilation of the stages.
In Stage 1, these are defined:
0x3E
0x40
0x41
0x42
0x44
0x48
0x1FE
0xAA55).
See the file `stage1/stage1.S', for more information.
In the first sector of Stage 1.5 and Stage 2, the block lists are
recorded between firstlist and lastlist. The address of
lastlist is determined when assembling the file
`stage2/start.S'.
The trick here is that it is actually read backward, and the first 8-byte block list is not read here, but after the pointer is decremented 8 bytes, then after reading it, it decrements again, reads, and so on, until it is finished. The terminating condition is when the number of sectors to be read in the next block list is zero.
The format of a block list can be seen from the example in the code just
before the firstlist label. Note that it is always from the
beginning of the disk, but not relative to the partition
boundaries.
In the second sector of Stage 1.5 and Stage 2, these are defined:
0x6
0x8
0xC
0x10
0x11
0x12
0x12 + the length of the version string
See the file `stage2/asm.S', for more information.
For any particular partition, it is presumed that only one of the normal filesystems such as FAT, FFS, or ext2fs can be used, so there is a switch table managed by the functions in `disk_io.c'. The notation is that you can only mount one at a time.
The block list filesystem has a special place in the system. In addition to the normal filesystem (or even without one mounted), you can access disk blocks directly (in the indicated partition) via the block list notation. Using the block list filesystem doesn't effect any other filesystem mounts.
The variables which can be read by the filesystem backend are:
current_drive
current_partition
current_slice
saved_drive
saved_partition
part_start
part_length
print_possibilities
dir function should print the possible completions
of a file, and false when it should try to actually open a file of that
name.
FSYS_BUF
The variables which need to be written by a filesystem backend are:
filepos
filemax
disk_read_func
NULL at all other times (it will be NULL by
default). If this isn't done correctly, then the @command{testload} and
@command{install} commands won't work correctly.
The functions expected to be used by the filesystem backend are:
devread
grub_read
grub_read can be
used, after setting block_file to 1.
print_a_completion
print_a_completion for
each possible file name. Otherwise, the file name completion won't work.
The functions expected to be defined by the filesystem backend are described at least moderately in the file `filesys.h'. Their usage is fairly evident from their use in the functions in `disk_io.c', look for the use of the fsys_table array.
Caution: The semantics are such that then `mount'ing the
filesystem, presume the filesystem buffer FSYS_BUF is corrupted,
and (re-)load all important contents. When opening and reading a file,
presume that the data from the `mount' is available, and doesn't
get corrupted by the open/read (i.e. multiple opens and/or reads will be
done with only one mount if in the same filesystem).
GRUB built-in commands are defined in a uniformal interface, whether they are menu-specific or can be used anywhere. The definition of a builtin command consists of two parts: the code itself and the table of the information.
The code must be a function which takes two arguments, a command-line string and flags, and returns an `int' value. The flags argument specifies how the function is called, using a bit mask. The return value must be zero if successful, otherwise non-zero. So it is normally enough to return errnum.
The table of the information is represented by the structure
struct builtin, which contains the name of the command, a pointer
to the function, flags, a short description of the command and a long
description of the command. Since the descriptions are used only for
help messages interactively, you don't have to define them, if the
command may not be called interactively (such as @command{title}).
The table is finally registered in the table builtin_table, so
that run_script and enter_cmdline can find the
command. See the files `cmdline.c' and `builtins.c', for more
details.
The disk space can be used in a boot loader is very restricted because a MBR (see section The structure of Master Boot Record) is only 512 bytes but it also contains a partition table (see section The format of partition tables) and a BPB. So the question is how to make a boot loader code enough small to be fit in a MBR.
However, GRUB is a very large program, so we break GRUB into 2 (or 3) distinct components, Stage 1 and Stage 2 (and optionally Stage 1.5). See section The memory map of various components, for more information.
We embed Stage 1 in a MBR or in the boot sector of a partition, and place Stage 2 in a filesystem. The optional Stage 1.5 can be installed in a filesystem, in the boot loader area in a FFS or a ReiserFS, and in the sectors right after a MBR, because Stage 1.5 is enough small and the sectors right after a MBR is normally an unused region. The size of this region is the number of sectors per head minus 1.
Thus, all Stage1 must do is just load Stage2 or Stage1.5. But even if Stage 1 needs not to support the user interface or the filesystem interface, it is impossible to make Stage 1 less than 400 bytes, because GRUB should support both the CHS mode and the LBA mode (see section INT 13H disk I/O interrupts).
The solution used by GRUB is that Stage 1 loads only the first sector of Stage 2 (or Stage 1.5) and Stage 2 itself loads the rest. The flow of Stage 1 is:
The flow of Stage 2 (and Stage 1.5) is:
Note that Stage 2 (or Stage 1.5) does not probe the geometry or the accessing mode of the loading drive, since Stage 1 has already probed them.
FIXME: I will write this chapter after implementing the new technique.
FIXME: I doubt if Erich didn't write this chapter only himself wholly, so I will rewrite this chapter.
FIXME: I'm not sure where some part of the original chapter is derived, so I will rewrite this chapter.
FIXME: Likewise.
FIXME: Probably the original chapter is derived from "How It Works", so I will rewrite this chapter.
When you write patches for GRUB, please send them to the mailing list [email protected]. Here is the list of items of which you should take care:
chain-load is the mechanism for loading unsupported operating systems by loading another boot loader. It is typically used for loading DOS or Windows.
There are a few pathological cases where loading a very badly organized ELF kernel might take longer, but in practice this never happen.
The LInux LOader, a boot loader that everybody uses, but nobody likes.
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
This is not necessary for most of the modern operating systems.
RARP is deprecated, since it cannot serve much information
However, this behavior will be changed in the future version, in a user-invisible way.
The latter feature has not been implemented yet.
They're loaded the same way, so we will refer to the Stage 1.5 as a Stage 2 from now on.
I can't imagine why you want to do such a thing, though
This document was generated on 15 October 2001 using the texi2html translator version 1.54.