How to Create a USB boot disk for a Linux operating system

USB flash memory storage device (USB flash drive) is lightweight, exquisite, easy to use, easy to carry, and other advantages. In particular, compared with a floppy disk, it features large capacity, high security and reliability, and fast reading speed, more and more people are using this device to replace the floppy disk and swap files between PCs. Currently, the new motherboard BIOS supports USB floppy disk and hard disk boot methods, which makes Windows system maintenance and installation more convenient. However, manufacturers only provide tools to create Windows 98 boot disks, but not linux boot disks. Creating a Linux boot disk on a USB flash drive is more practical for system maintenance personnel. You can use Linux to build a small kernel and a network environment, quickly identifies and resolves network faults and transfers files. This document uses Red Hat as an example to create a Linux boot disk with a dual-boot USB flash drive.

Download related software: e3, bvi, and Linux kernel.

Compile the kernel

First, the computer's motherboard must support the USB hard drive boot mode, and the used USB flash drive is the boot type.

I take Linux-2.4.20 as an example. During compilation, be sure not to compile unnecessary modules, such as sound card drivers, so that the compiled kernel is as small as possible. To support usb Flash boot, you must compile SCSI devices, usb core, usb-storage, Loopback device support, RAM disk support, and initrd into the kernel.

Many people may ask why the usb-storage module is already included in the kernel to create an initrd. imgfile? This is because the initialization process of the USB flash drive is slower than the execution of/sbin/init. As a result, the kernel has been started and the initialization of the USB flash drive has not been completed. Therefore, the root file system has not been loaded, at this time, the execution of the/sbin/init command is definitely not successful. Create an initrd. imgfile to load the initrd. imgfile to the memory when the kernel is started. wait 3 seconds for the USB flash drive to complete initialization and then execute the/sbin/init command. The procedure is as follows.

1. Create an initrd. imgfile

# mkdir -p /mnt/initrd # cd /tmp # mkinitrd /tmp/initrd.gz 2.4.20-usb

2. decompress the initrd. imgfile and modify the startup script linuxrc.

# gunzip initrd.gz # mount -o loop /tmp/initrd /mnt/initrd # cp /sbin/busybox /mnt/initrd/bin # cd /mnt/initrd/bin # ln -s busybox sleep # vi /mnt/initrd/linuxrc

Add the following content:

echo 'wait 3 seconds.....' /bin/sleep 3

3. regenerate the initrd. imgfile

Because the default initrd file is large (4 MB), you must reduce it to speed up the startup of the USB flash drive. The procedure is as follows:

# mkdir -p /mnt/initrdusb # cd /tmp # dd if =/dev/zero of= /tmp/initrdusb bs=1M count=1 # mke2fs -m 0 initrdusb # mount -o loop /tmp/initrdusb /mnt/initrdusb # cp -a /mnt/initrd/* /mnt/initrdusb # umount /mnt/initrd # umount /mnt/initrdusb # cd /tmp # gzip -9 initrdusb # cp initrdusb.gz /boot/initrd-2.4.20-usb.img

4. test whether the compiled kernel is properly started.

Test whether the compiled kernel is started normally and whether the information about the USB flash drive is visible during startup.

Create a boot disk

1. Divide the USB flash drive into two partitions.

The size of the partition size for Linux depends on which system maintenance tools are installed. The result is as follows:

# modprobe usb-storage # fdisk -l /dev/sda Disk /dev/sda: 16 heads, 63 sectors, 126 cylinders Units = cylinders of 1008 * 512 bytes Device Boot Start End Blocks Id System /dev/sda1 1 102 51376+ 6 FAT16 /dev/sda2 103 126 12096 83 Linux

Note: If you need To Boot Windows 98 with a USB flash drive, the slice size must be set to 63. You can use the fdisk x command to expand and modify the parameters of heads, sectors, and cylinders.

2. Create and generate ext2 partitions

# mke2fs -m 0 /dev/sda2 # mkdir -p /mnt/sda2 # mount /dev/sda2 /mnt/sda2 # cd /mnt/sda2

3. Create a boot directory

Copy the compiled kernel and initrd-2.4.20-usb.img files to the boot directory, the compiled modules to the lib/modules directory, and copy the/boot/grub files to the boot directory, edit boot/grub/menu. the content of the lst file is as follows:

timeout 10 color 0x17 0x70 default 0 title Windows 98 rootnoverify (hd0,0) makeactive chainloader +1 title GNU/Linux Redhat 8.0 (2.4.20-usb) root (hd0,1) kernel /boot/vmlinuz-2.4.20-usb ro root=/dev/sda2 initrd /boot/initrd-2.4.20-usb.img

To install grub, perform the following operations:

grub> root (hd1,1) grub> setup (hd1)

4. Create a bin directory

Copy System maintenance tools such as insmod, fsck, and mkdosfs as needed. Be sure to use the ldd command to check the shared library files. These files need to be copied to the lib directory according to the original path. Due to disk space restrictions, busybox commands are used to replace some common Linux commands. The main reason is that the busybox file is very small and is statically linked, including many common Linux commands such as cat, init, ifconig, and route) Use ln-s busybox to establish symbolic connections to these files. You can re-compile busybox as needed, including vi and other commands, or use small e3 to replace vi.

In addition, if bash is used, you must edit and cut/etc/termcap and the following files:

/bin/bash /etc/termcap /usr/share/terminfo/l/linux /usr/share/terminfo/k/klone+acs /usr/share/terminfo/k/klone+color /usr/share/terminfo/k/klone+sgr

5. Create the dev directory

Run the cp-a command to copy common device files, including devices such as console, tty1, tty2, tty3sda, sda1, sda2, hda, hdb, and hda1.

6. Edit etc/init. d/rcS

The content is as follows:

#!/bin/sh PATH=/sbin:/bin export PATH mount -n -t proc none /proc umount /initrd mount -n -o remount,rw / mount -n -o remount,rw -t proc none /proc ifconfig lo 127.0.0.1

7. Edit the etc/fstab file

The content is as follows:

/dev/sda2 / ext2 defaults 1 1 none /proc proc defaults 0 0

Application Example

Here is an example of transferring files. Run:

$ tar cf - win98 | nc -l -p 5555

Note: You can use the USB flash drive to start the machine on machine B and telnet to machine A to execute the above commands. Run the following command on machine B with a USB flash drive:

# mount -t vfat -o codepage=938,iocharset=cp936 /dev/hda5 /mnt/2dos # cd /mnt/2dos # modprobe eepro00 # ifconfig eth0 192.168.1.10 # route add default gw 192.168.1.1 # ping 192.168.10.5 # nc 192.168.10.5 5555 | tar xf -

If you cannot create a Windows 98 boot disk by using the format/s command, you can use the following method:

# mkdosfs -F 16 /dev/sda1 # xxd -c 16 /dev/sda1 | less

Record the Boot Record 32 ~ In this example, the 35-byte content is 60 91 01 00, which records the total number of sectors in the FAT partition). Then, use the tool provided by longke to create a boot disk for Windows 98, then, use the bvi in Linux or the tool that can edit the binary file to modify the 32 ~ Boot Record ~ 35 bytes is the original content. In this way, we can implement a three-way Windows Dual Boot + Linux boot ).