Introduction and production of Linux inird

Linux Kernel since 2.6 version, it is strongly recommended CPIO-INITRD.

Currently, initrd of major Linux releases are in the cpio format.

How to Make CPIO-INITRD.

First, let's assume that we have used busybox, klibc, or anything else to prepare the root file system ~ /Rootfs.

As mentioned in IBM developerworks, you can use the following command to make a CPIO-INITRD:

Cd ~ /Rootfs
Find. | cpio-c-o> ../initrd. img
Gzip ../initrd. img

In fact, this is not correct.

I use these commands to make a CPIO-INITRD and the results are all kernel panic.

Refer to the script code of the mkinitcpio command of my archlinux release, it should be to use gen_init_cpio command to make CPIO-INITRD.

The source code of the gen_init_cpio command is usually packaged together with the Linux kernel source code, which is located in the usr/directory of the kernel source code.

Compile the source code to obtain the gen_init_cpio executable file, which is not enough.

The parameter of gen_init_cpio is a text file whose content is similar to this format:

DIR/sbin 755 0 0
Slink/sbin/makedevs ../bin/busybox 777 0 0
Slink/sbin/modprobe ../bin/busybox 777 0 0
Slink/sbin/switch_root ../bin/busybox 777 0 0
Slink/sbin/sysctl ../bin/busybox 777 0 0
Slink/sbin/lsmod ../bin/busybox 777 0 0
Slink/sbin/Getty ../bin/busybox 777 0 0
Slink/sbin/ifconfig ../bin/busybox 777 0 0
......

Obviously, this is a file list.

It is unrealistic to manually create this file list. The usr/directory contains gen_initramfs_list.sh, which is used to automatically generate the file list.

Well, we can come up with the complete steps to generate a CPIO-INITRD:

Cd ~
Gen_initramfs_list.sh rootfs/> filelist
Gen_init_cpio filelist> rootfs. cpio
Gzip rootfs. cpio

The last rootfs.cpio.gz is our CPIO-INITRD.

Modify the following parameters in Bootloader:

Append initrd1_rootfs.cpio.gz ramdisk_size = 8192 VGA = 792

What are the results?

(Full text)

==============================================

The initrd. IMG In the 2.6 kernel adopts cpio compression and is no longer in the ext2 format used by the 2.4 kernel. 1. Decompress initrd ***. IMG:
# Cp/boot/initrd-***. IMG initrd.img.gz
# Gunzip initrd.img.gz
# Mkdir initrd
# Mv initrd. IMG initrd
# Cd initrd
# Cpio-ivmd <initrd. IMG 2. Modify initrd
Modify the unzipped initrd file system. 3. generate a new initrd
# Find. | cpio-o-h NEWC | gzip>/mnt/sda1/boot/initrd. img-2.6.18-4-686

(Note:-h newc is required; otherwise, the kernel will consider it as ramdisk rather than initramfs)

 

Reference link:

Linux initial RAM disk (initrd) Overview

Http://www.ibm.com/developerworks/cn/linux/l-initrd.html
Analysis of initrd mechanism in linux2.6 Kernel

Http://www.ibm.com/developerworks/cn/linux/l-k26initrd/index.html