It can be seen that boot loader is the second program to be executed during computer startup, and it is the key program to guide the operating system. Boot Loader that can guide the operating system mainly includes Lilo, grub, and MBR programs in windows. Grub is one of the most widely used and excellent boot Bootstrap programs. 51testing software testing network Phal % ~. GD
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Grub involves several important files:
The first one is stage1. It is installed in the MBR sector (1st sectors of 0-sided 0 channels), with a size of 512 bytes (446-byte code + 64-byte Partition Table + 2-byte flag 55aa ), it is responsible for loading the Start Program stored in zero-face, zero-track, and 2nd-sector. The second is stage1_5. Stage00005 is responsible for identifying file systems and loading stage2, so stage00005 often has multiple to support reading from different file systems. When grub is installed, grub loads the corresponding stage00005 to 3rd sectors of the 0-side 0 track based on the current/boot/partition type. Stage1_5 is loaded by START. The third is stage2. It displays the boot menu and provides user interaction interfaces, and loads the operating system kernel based on user selection or default configuration. Unlike the first two files, stage2 is stored on the disk/boot/grub. The fourth is menu. lst (/boot/GRUB/grub. conf link ). Grub. conf is a script-based text file that contains the configuration displayed in the menu and the kernel loading configuration of each operating system. Grub displays the Startup menu based on grub. conf and provides an interactive interface with the user. Grub loads the corresponding kernel program based on the selected or default configuration and grub. conf Kernel configuration, and gives control to the kernel program, so that the kernel program can start the real operating system. In addition to the main files described above, grub also includes some disk programs that support interactive functions. It mainly includes grub, grub-install, grub-md5-crypt and grub-terminfo and/usr/bin/mbchk under/sbin/, as well as the device image file (device.map)and menu single background file (splash.xpm.gz) under/sbin ). Through the above analysis, we can easily see that grub actually contains two parts, one of which is installed in the special sector of the disk, and the other part exists as a file. To enable grub to start the operating system, you must first install grub's stage1 and stage00005 (automatically select whether to install according to the file system) to the special sector of the disk. In addition, grub exists in the disk/boot/grub. conf, device. map and other files and programs supporting interaction, and these programs must be in the path specified by the PATH environment variable. With this knowledge, we believe that it is not difficult to install, configure, back up, or repair grub. 51testing software testing network q) TT |/| #?51testing software testing network uho0mj * BM
GrubConfiguration File example
#=========================/ Boot/GRUB/grub. confFile examples============================51testing software testing network 0z ^ s + r2x (_ r C6 ~ C # l
Timeout 30 # Wait for the time (in seconds) for the menu item to be selected. If the time-out period is exceeded, the default option 51testing Software Testing Network s YZR }? 3Y
Default 0 # default option, option 1: 51testing software testing network Q # [MSN,} I sm
Fallback 1 # If the first item fails, start the following Backup option 51testing software testing network F/sa0b9n} 1q
Splashimage = (hd0, 0)/GRUB/splash.xpm.gz # grub startup Screen
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B _/J] W * \ x0titlered Hat Linux Enterprise as3 for syd168 # menu title of the startup Item
JC "Crk" l0root (hd0, 0) # specify the root file system, which is/boot of 1st hard disks in 1st sectors. 51testing Software Testing Network | 'lm/i6f7e @ # Yu
Kernel/vmlinuz-2.4.18 Ro root = label =/# kernel in/boot
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#StartWindowsIf onlyLinuxNo51testing qhg. D * C $ L: y6pc
Title Windows2003 enterprise for syd168 # Windows Startup menu title
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In/z "E; D0#=========================/ Boot/GRUB/grub. confFile examples============================
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Linuxer around the world knows what grub is, but many friends may be confused about the process from MBR to grub and then to the specific operating system. This is not the case. A friend of Cu sent such a help post:
If a computer is installed with Win2000, I am now installing Linux and grub. If grub is installed in the primary partition, grub will directly guide Linux and win2000, I can understand, because the MBR contains grub stage1 (right ?), MBR guides the system to jump to DBR (active partition) by checking the DPT partition information. When will the active partition be set? So how does one handle the win boot information in the MBR when grub is installed in the MBR? Is it true that when grub is installed to MBR, grub will set the partition where grub is located as the active partition? Then, during GRUB boot, MBR will find the active partition and find the desired file, and then continue? Assume that grub is installedOthersPartition (non-primary boot zone), how does one implement grub first? Isn't MBR first? Since it has been installed in other partitions and has not been changed to the primary boot zone, the primary boot zone is still the Win2000 boot data. How can grub be started first? Why? Is it related to the active partition? I can see which system is written in the data, and which system is started as the active partition. However, it seems that there is no way to explain it, that is, at the very beginning, I have never understood it, but I cannot understand it clearly.
The following is a summary of the analysis and discussion on this issue by each Cu player.
First, let's take a look at the traditional boot process: loading and running Master Boot Record (MBR) Main Boot zone content (such as lilo ). Scan the partition table, locate the active partition, and load the content of the pilot sector on the active partition to the memory for execution.
SystemGuiding ProcessIt consists of the following steps (taking hard drive as an example)
1. Start the instance;
2. BIOS power-on self-test (post -- power on self test). The memory address is 0fff: 0000;
3. Read the first sector of the hard disk (0-headed, 0-way, 1-sector, that is, Boot Sector) into the memory address 0000: 7c00;
4. Check (Word) 0000: 7dfe whether it is equal to 0xaa55. If it is not equal to, it resends to try other media. If there is no other starting media, it displays "no rom basic" and then crashes;
5. Jump to 0000: Execute the MBR program at 7c00;
6. Copy the MBR to 0000: 0600 and continue the execution;
7. Search for active partitions in the primary partition table. If no active partition is found or more than one active partition is found, stop;
8. Read the first sector of the active partition into the memory address 0000: 7c00;
9. Check (Word) 0000: 7dfe whether it is equal to 0xaa55. If it is not equal, "missing Operating System" is displayed, and then stop, or try to start a floppy disk;
10. Jump to 0000: 7c00 and continue executing the Startup Program of the specific system;
11. Start the system.
When grub is installed to a logical partition, the logical partition loaded by grub must be set as active. However, at this time, grub took over the action after 11 steps: Read grub. conf from stage 1.5. The configuration and user selection determine the next Bootstrap action.
Grub is usually installed in two cases. For MBR installation, grub directly overwrites the original MBR boot program. This is why we need to switch back to the "original Windows boot mode". We only need to use DOS to boot fdisk/MBR. Note that 0000: 7c00 appears in two places in step 1-11. Whether it is dos boot sector or NT loader, it runs from 0000: 7c00. In fact, this small program for developing partition management in MS is equivalent to inserting it in BIOS Boot Sector. Grub is also written as a subroutine starting from the memory of 0000: 7c00, so it can be loaded by BIOS and dos mbr.
After self-check, the boot right is handed over to the hard disk MBR, and grub is started. Windows/Linux can be guided by grub. Note: Linux does not have to be installed in the active partition, because the boot program is in the MBR! However, windows must be installed in the active partition (bootable windows). The second windows may not be installed in the active partition, but its boot file must be in the active partition.
The general order is:
Grub --> Windows-> Find boot file-boot loading-start Windows
Grub --> Linux-> Find the boot file (/BOOT)-> Boot Load-start Linux
If grub is installed on another partition, isn't it MBR? This is the primary partition where grub is installed. It must be set as an active partition. Because MBR (physical master boot partition) does not actually have OS-related boot programs, MBR usually only scans and reads the subsequent Partition Table and finds the corresponding active partition, read the 512-byte program of the first sector of the corresponding active partition and run it. This program is responsible for guiding the corresponding system of the corresponding partition step by step. Therefore, the approximate running order is
BiOS> MBR> grub> menu.
In this way, the actual process can be summarized as follows:
1. Start the instance;
2. BIOS power-on self-test (post -- power on self test). The memory address is 0fff: 0000;
3. Read the first sector of the hard disk (0-headed, 0-way, 1-sector, that is, Boot Sector) into the memory address 0000: 7c00;
4. Check (Word) 0000: 7dfe whether it is equal to 0xaa55. If it is not equal to, it resends to try other media. If there is no other starting media, it displays "no rom basic" and then crashes;
5. Jump to 0000: Execute the MBR program at 7c00;
6. MBR first copies itself to 0000: 0600, and then continues to execute. If XP is installed first and Linux is not installed in MBR, then the data in this MBR is still the data written by win, it is used to search for active partitions in the primary partition table. In this case, you must set the primary partition where grub is located as the active partition, in this case, grub can be started normally, and stage1 of grub can be tuned to stage1.5 and others to guide the entire system. If you install XP first and then Linux, but grub is installed in MBR, stage1 is directly transferred to the memory, and stage1 is calling stage1.5 and stage2 to guide the system. At this time, you do not need to set the primary partition of other grub files as active partitions. It directly calls stage1.5, and then calls stage2 to identify the file system, to enable multi-start.
7. Search for active partitions in the primary partition table. If no active partition is found or more than one active partition is found, stop;
8. Read the first sector of the active partition into the memory address 0000: 7c00;
9. Check (Word) 0000: 7dfe whether it is equal to 0xaa55. If it is not equal, "missing Operating System" is displayed, and then stop, or try to start a floppy disk;
10. Jump to 0000: 7c00 and continue executing the Startup Program of the specific system;
11. Start the system.
A little bit of information:
Grub that can work normally should include the following files: stage1, stage2, * stage1_5, menu. lst.
The size of stage1 must be 512 bytes. It must be installed (written to) the Master Boot Record of a hard disk or an active partition (this partition should be marked with fdisk as bootable). The primary and only role of stage1 is to find the stage2 file that you store somewhere on the hard disk to complete subsequent work.
Stage2 files can exist in a specific file system. For example, if you split a LINUX partition and create an ext2 file system on it, copy the file to a directory in the partition. You can also store stage2 directly in a location on the hard disk, that is, a location not partitioned. However, it seems that not many people will do this.
Because the capacity of stage1 is limited (the size of the Master Boot Record MBR and the startup sector can only be 512 bytes), it cannot be identified by the file system, if you store stage2 on an ext2 or fat file system, how can you find this file? This requires the stage00005 files mentioned above, which are responsible for interpreting the file system. The corresponding stage00005 file must be called when stage2 is placed on a file system in what format. For example, if you store stage2 in the ext2 format file system, e2fs_stage1_5 is required; if stage2 is stored in the fat format file system, fat_stage1_5 is required.
Reference Source:
1thuud ~ 3b4g0ftp: // alpha.gnu.org/gnu/grub/51testingsoftware testing network 2oz'nls (R '~ \
Http://www.linuxeden.com/html/sysadmin/20070530/26936.html51testingsoftware testing network 4pcz7kuswe
Http://soft.zdnet.com.cn/software_zone/2007/1006/537431.shtml
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