Linux/initrd

initrd
Extract initrd image: cat initrd.img | gzip -d | cpio -dmvi gunzip < /boot/initrd.img | cpio -i --make-directories gzip -dc /boot/initrd-2.6.16-026test014.4-smp.cpio | cpio -id gunzip initrd.cpio.gz cpio -iI initrd.cpio

Build initd image: find ./ | cpio -H newc -o | gzip > ../initrd.img

find ./ | cpio -H newc -o > initrd.cpio gzip initrd.cpio mv initrd.cpio.gz initrd.img

Build within chroot: mount /dev/sda1 /mnt chroot /mnt /sbin/mkinitrd /boot/initrd.img 3.10.0 # /lib/modules

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Extract initramfs:

If the output of file -L /initrd.img is ASCII cpio archive (SVR4 with no CRC), consider the initrd image to have microcode prepended.

extract the microcode by and take node of the blocks in the STDERR display (in my case 48). cd path/to/initrd/; cpio -i </initrd.img

extract the basic initrd by (adjust skip values matching the cpio STDERR output). cd path/to/initrad/; dd if=/initrd.img of=initrd.img bs=512 skip=48; zcat initrd.img |cpio -i

Otherwise, extract the initrd directly by cd path/to/initrad/; zcat /initrd.img |cpio -i

References:
 * Extracting initrd image - Linux Forums
 * Modifying initrd image - OpenVZ Wiki
 * Re: opensuse extract and modify initrd

CentOS 5.7
Tree structure: `-- sysroot
 * -- bin
 * |-- dmraid
 * |-- insmod
 * |-- kpartx
 * |-- modprobe -> /sbin/nash
 * `-- nash
 * -- dev
 * |-- console
 * |-- mapper
 * |-- null
 * |-- ptmx
 * |-- ram -> ram1
 * |-- ram0
 * |-- ram1
 * |-- rtc
 * |-- systty
 * |-- tty
 * |-- tty0
 * |-- tty1
 * |-- tty10
 * |-- tty11
 * |-- tty12
 * |-- tty2
 * |-- tty3
 * |-- tty4
 * |-- tty5
 * |-- tty6
 * |-- tty7
 * |-- tty8
 * |-- tty9
 * |-- ttyS0
 * |-- ttyS1
 * |-- ttyS2
 * |-- ttyS3
 * `-- zero
 * -- etc
 * -- init
 * -- lib
 * |-- ata_piix.ko
 * |-- dm-log.ko
 * |-- dm-mem-cache.ko
 * |-- dm-message.ko
 * |-- dm-mod.ko
 * |-- dm-raid45.ko
 * |-- dm-region_hash.ko
 * |-- ehci-hcd.ko
 * |-- ext3.ko
 * |-- firmware
 * |-- jbd.ko
 * |-- libata.ko
 * |-- mptbase.ko
 * |-- mptscsih.ko
 * |-- mptspi.ko
 * |-- ohci-hcd.ko
 * |-- scsi_mod.ko
 * |-- scsi_transport_spi.ko
 * |-- sd_mod.ko
 * `-- uhci-hcd.ko
 * -- proc
 * -- sbin -> bin
 * -- sys

init:
 * 1) !/bin/nash

mount -t proc /proc /proc setquiet echo Mounting proc filesystem echo Mounting sysfs filesystem mount -t sysfs /sys /sys echo Creating /dev mount -o mode=0755 -t tmpfs /dev /dev mkdir /dev/pts mount -t devpts -o gid=5,mode=620 /dev/pts /dev/pts mkdir /dev/shm mkdir /dev/mapper echo Creating initial device nodes mknod /dev/null c 1 3 mknod /dev/zero c 1 5 mknod /dev/urandom c 1 9 mknod /dev/systty c 4 0 mknod /dev/tty c 5 0 mknod /dev/console c 5 1 mknod /dev/ptmx c 5 2 mknod /dev/rtc c 10 135 mknod /dev/tty0 c 4 0 mknod /dev/tty1 c 4 1 mknod /dev/tty2 c 4 2 mknod /dev/tty3 c 4 3 mknod /dev/tty4 c 4 4 mknod /dev/tty5 c 4 5 mknod /dev/tty6 c 4 6 mknod /dev/tty7 c 4 7 mknod /dev/tty8 c 4 8 mknod /dev/tty9 c 4 9 mknod /dev/tty10 c 4 10 mknod /dev/tty11 c 4 11 mknod /dev/tty12 c 4 12 mknod /dev/ttyS0 c 4 64 mknod /dev/ttyS1 c 4 65 mknod /dev/ttyS2 c 4 66 mknod /dev/ttyS3 c 4 67 echo Setting up hotplug. hotplug echo Creating block device nodes. mkblkdevs echo "Loading ehci-hcd.ko module" insmod /lib/ehci-hcd.ko echo "Loading ohci-hcd.ko module" insmod /lib/ohci-hcd.ko echo "Loading uhci-hcd.ko module" insmod /lib/uhci-hcd.ko mount -t usbfs /proc/bus/usb /proc/bus/usb echo "Loading jbd.ko module" insmod /lib/jbd.ko echo "Loading ext3.ko module" insmod /lib/ext3.ko echo "Loading scsi_mod.ko module" insmod /lib/scsi_mod.ko echo "Loading sd_mod.ko module" insmod /lib/sd_mod.ko echo "Loading scsi_transport_spi.ko module" insmod /lib/scsi_transport_spi.ko echo "Loading mptbase.ko module" insmod /lib/mptbase.ko echo "Loading mptscsih.ko module" insmod /lib/mptscsih.ko echo "Loading mptspi.ko module" insmod /lib/mptspi.ko echo "Loading libata.ko module" insmod /lib/libata.ko echo "Loading ata_piix.ko module" insmod /lib/ata_piix.ko echo "Loading dm-mem-cache.ko module" insmod /lib/dm-mem-cache.ko echo "Loading dm-mod.ko module" insmod /lib/dm-mod.ko echo "Loading dm-log.ko module" insmod /lib/dm-log.ko echo "Loading dm-region_hash.ko module" insmod /lib/dm-region_hash.ko echo "Loading dm-message.ko module" insmod /lib/dm-message.ko echo "Loading dm-raid45.ko module" insmod /lib/dm-raid45.ko echo Waiting for driver initialization. stabilized --hash --interval 1000 /proc/scsi/scsi mkblkdevs echo Scanning and configuring dmraid supported devices resume LABEL=SWAP-sda2 echo Creating root device. mkrootdev -t ext3 -o defaults,ro /dev/sda3 echo Mounting root filesystem. mount /sysroot echo Setting up other filesystems. setuproot echo Switching to new root and running init. switchroot

CentOS 5.7 Boot from USB stick to NFS root
Tree structure: `-- var `-- lib `-- dhclient
 * -- bin
 * |-- dmraid
 * |-- insmod
 * |-- kpartx
 * |-- modprobe -> /sbin/nash
 * `-- nash
 * -- dev
 * |-- console
 * |-- mapper
 * |-- null
 * |-- ptmx
 * |-- ram -> ram1
 * |-- ram0
 * |-- ram1
 * |-- rtc
 * |-- systty
 * |-- tty
 * |-- tty0
 * |-- tty1
 * |-- tty10
 * |-- tty11
 * |-- tty12
 * |-- tty2
 * |-- tty3
 * |-- tty4
 * |-- tty5
 * |-- tty6
 * |-- tty7
 * |-- tty8
 * |-- tty9
 * |-- ttyS0
 * |-- ttyS1
 * |-- ttyS2
 * |-- ttyS3
 * `-- zero
 * -- etc
 * -- init
 * -- lib
 * |-- ata_piix.ko
 * |-- dm-log.ko
 * |-- dm-mem-cache.ko
 * |-- dm-message.ko
 * |-- dm-mod.ko
 * |-- dm-raid45.ko
 * |-- dm-region_hash.ko
 * |-- e1000e.ko
 * |-- ehci-hcd.ko
 * |-- firmware
 * |-- libata.ko
 * |-- libsas.ko
 * |-- lockd.ko
 * |-- mvsas.ko
 * |-- nfs.ko
 * |-- nfs_acl.ko
 * |-- ohci-hcd.ko
 * |-- pata_marvell.ko
 * |-- scsi_mod.ko
 * |-- scsi_transport_sas.ko
 * |-- sd_mod.ko
 * |-- sunrpc.ko
 * |-- uhci-hcd.ko
 * `-- usb-storage.ko
 * -- proc
 * -- sbin -> bin
 * -- sys
 * -- sysroot

initrd
 * 1) !/bin/nash

mount -t proc /proc /proc setquiet echo Mounting proc filesystem echo Mounting sysfs filesystem mount -t sysfs /sys /sys echo Creating /dev mount -o mode=0755 -t tmpfs /dev /dev mkdir /dev/pts mount -t devpts -o gid=5,mode=620 /dev/pts /dev/pts mkdir /dev/shm mkdir /dev/mapper echo Creating initial device nodes mknod /dev/null c 1 3 mknod /dev/zero c 1 5 mknod /dev/urandom c 1 9 mknod /dev/systty c 4 0 mknod /dev/tty c 5 0 mknod /dev/console c 5 1 mknod /dev/ptmx c 5 2 mknod /dev/rtc c 10 135 mknod /dev/tty0 c 4 0 mknod /dev/tty1 c 4 1 mknod /dev/tty2 c 4 2 mknod /dev/tty3 c 4 3 mknod /dev/tty4 c 4 4 mknod /dev/tty5 c 4 5 mknod /dev/tty6 c 4 6 mknod /dev/tty7 c 4 7 mknod /dev/tty8 c 4 8 mknod /dev/tty9 c 4 9 mknod /dev/tty10 c 4 10 mknod /dev/tty11 c 4 11 mknod /dev/tty12 c 4 12 mknod /dev/ttyS0 c 4 64 mknod /dev/ttyS1 c 4 65 mknod /dev/ttyS2 c 4 66 mknod /dev/ttyS3 c 4 67 echo Setting up hotplug. hotplug echo Creating block device nodes. mkblkdevs echo "Loading ehci-hcd.ko module" insmod /lib/ehci-hcd.ko echo "Loading ohci-hcd.ko module" insmod /lib/ohci-hcd.ko echo "Loading uhci-hcd.ko module" insmod /lib/uhci-hcd.ko mount -t usbfs /proc/bus/usb /proc/bus/usb echo "Loading sunrpc.ko module" insmod /lib/sunrpc.ko echo "Loading nfs_acl.ko module" insmod /lib/nfs_acl.ko echo "Loading lockd.ko module" insmod /lib/lockd.ko echo "Loading nfs.ko module" insmod /lib/nfs.ko echo "Loading e1000e.ko module" insmod /lib/e1000e.ko echo Bringing up eth2 netname 00:1B:21:94:6A:21 eth2 network --device eth2 --bootproto dhcp rename /var/lib/dhclient/dhclient.leases /var/lib/dhclient/dhclient-eth2.leases echo "Loading scsi_mod.ko module" insmod /lib/scsi_mod.ko echo "Loading sd_mod.ko module" insmod /lib/sd_mod.ko echo "Loading scsi_transport_sas.ko module" insmod /lib/scsi_transport_sas.ko echo "Loading libata.ko module" insmod /lib/libata.ko echo "Loading libsas.ko module" insmod /lib/libsas.ko echo "Loading mvsas.ko module" insmod /lib/mvsas.ko echo "Loading pata_marvell.ko module" insmod /lib/pata_marvell.ko echo "Loading ata_piix.ko module" insmod /lib/ata_piix.ko echo "Loading usb-storage.ko module" insmod /lib/usb-storage.ko echo Waiting for driver initialization. stabilized /proc/bus/usb/devices echo "Loading dm-mem-cache.ko module" insmod /lib/dm-mem-cache.ko echo "Loading dm-mod.ko module" insmod /lib/dm-mod.ko echo "Loading dm-log.ko module" insmod /lib/dm-log.ko echo "Loading dm-region_hash.ko module" insmod /lib/dm-region_hash.ko echo "Loading dm-message.ko module" insmod /lib/dm-message.ko echo "Loading dm-raid45.ko module" insmod /lib/dm-raid45.ko echo Waiting for driver initialization. stabilized --hash --interval 1000 /proc/scsi/scsi mkblkdevs echo Scanning and configuring dmraid supported devices echo Creating root device. mkrootdev -t nfs -o rsize=8192,wsize=8192,timeo=14,intr 10.50.8.120:/home/esx/ken/kesx echo Mounting root filesystem. mount /sysroot echo Setting up other filesystems. setuproot echo Copying DHCP lease for eth2 cp /var/lib/dhclient/dhclient-eth2.leases /sysroot/dev/.dhclient-eth2.leases echo Switching to new root and running init. switchroot