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2026-05-07T03:46:27Z
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Kenneth: /* initrd */
2019-04-29T23:54:46Z
<p><span dir="auto"><span class="autocomment">initrd</span></span></p>
<p><b>New page</b></p><div>== initrd ==<br />
<br />
Extract initrd image:<br />
cat initrd.img | gzip -d | cpio -dmvi<br />
<br />
gunzip < /boot/initrd.img | cpio -i --make-directories<br />
<br />
gzip -dc /boot/initrd-2.6.16-026test014.4-smp.cpio | cpio -id<br />
<br />
gunzip initrd.cpio.gz<br />
cpio -iI initrd.cpio<br />
<br />
Build initd image:<br />
find ./ | cpio -H newc -o | gzip > ../initrd.img<br />
<br />
find ./ | cpio -H newc -o > initrd.cpio<br />
gzip initrd.cpio<br />
mv initrd.cpio.gz initrd.img<br />
<br />
Build within chroot:<br />
mount /dev/sda1 /mnt<br />
chroot /mnt<br />
/sbin/mkinitrd /boot/initrd.img 3.10.0 # /lib/modules<br />
<br />
--<br />
<br />
Extract initramfs: [https://wiki.debian.org/initramfs]<br />
<br />
If the output of file -L /initrd.img is ASCII cpio archive (SVR4 with no CRC), consider the initrd image to have microcode prepended.<br />
<br />
extract the microcode by and take node of the blocks in the STDERR display (in my case 48).<br />
cd path/to/initrd/; cpio -i </initrd.img <br />
<br />
extract the basic initrd by (adjust skip values matching the cpio STDERR output).<br />
cd path/to/initrad/; dd if=/initrd.img of=initrd.img bs=512 skip=48; zcat initrd.img |cpio -i<br />
<br />
Otherwise, extract the initrd directly by<br />
cd path/to/initrad/; zcat /initrd.img |cpio -i<br />
<br />
<br />
References:<br />
* [http://www.linuxforums.org/forum/linux-kernel/82174-extracting-initrd-image.html Extracting initrd image - Linux Forums] <br />
* [http://wiki.openvz.org/Modifying_initrd_image Modifying initrd image - OpenVZ Wiki]<br />
* [http://linux.derkeiler.com/Mailing-Lists/SuSE/2007-07/msg00622.html Re: opensuse extract and modify initrd]<br />
<br />
== Sample initrd ==<br />
<br />
=== CentOS 5.7 ===<br />
<br />
Tree structure:<br />
<pre><br />
|-- bin<br />
| |-- dmraid<br />
| |-- insmod<br />
| |-- kpartx<br />
| |-- modprobe -> /sbin/nash<br />
| `-- nash<br />
|-- dev<br />
| |-- console<br />
| |-- mapper<br />
| |-- null<br />
| |-- ptmx<br />
| |-- ram -> ram1<br />
| |-- ram0<br />
| |-- ram1<br />
| |-- rtc<br />
| |-- systty<br />
| |-- tty<br />
| |-- tty0<br />
| |-- tty1<br />
| |-- tty10<br />
| |-- tty11<br />
| |-- tty12<br />
| |-- tty2<br />
| |-- tty3<br />
| |-- tty4<br />
| |-- tty5<br />
| |-- tty6<br />
| |-- tty7<br />
| |-- tty8<br />
| |-- tty9<br />
| |-- ttyS0<br />
| |-- ttyS1<br />
| |-- ttyS2<br />
| |-- ttyS3<br />
| `-- zero<br />
|-- etc<br />
|-- init<br />
|-- lib<br />
| |-- ata_piix.ko<br />
| |-- dm-log.ko<br />
| |-- dm-mem-cache.ko<br />
| |-- dm-message.ko<br />
| |-- dm-mod.ko<br />
| |-- dm-raid45.ko<br />
| |-- dm-region_hash.ko<br />
| |-- ehci-hcd.ko<br />
| |-- ext3.ko<br />
| |-- firmware<br />
| |-- jbd.ko<br />
| |-- libata.ko<br />
| |-- mptbase.ko<br />
| |-- mptscsih.ko<br />
| |-- mptspi.ko<br />
| |-- ohci-hcd.ko<br />
| |-- scsi_mod.ko<br />
| |-- scsi_transport_spi.ko<br />
| |-- sd_mod.ko<br />
| `-- uhci-hcd.ko<br />
|-- proc<br />
|-- sbin -> bin<br />
|-- sys<br />
`-- sysroot<br />
</pre><br />
<br />
init:<br />
<pre><br />
#!/bin/nash<br />
<br />
mount -t proc /proc /proc<br />
setquiet<br />
echo Mounting proc filesystem<br />
echo Mounting sysfs filesystem<br />
mount -t sysfs /sys /sys<br />
echo Creating /dev<br />
mount -o mode=0755 -t tmpfs /dev /dev<br />
mkdir /dev/pts<br />
mount -t devpts -o gid=5,mode=620 /dev/pts /dev/pts<br />
mkdir /dev/shm<br />
mkdir /dev/mapper<br />
echo Creating initial device nodes<br />
mknod /dev/null c 1 3<br />
mknod /dev/zero c 1 5<br />
mknod /dev/urandom c 1 9<br />
mknod /dev/systty c 4 0<br />
mknod /dev/tty c 5 0<br />
mknod /dev/console c 5 1<br />
mknod /dev/ptmx c 5 2<br />
mknod /dev/rtc c 10 135<br />
mknod /dev/tty0 c 4 0<br />
mknod /dev/tty1 c 4 1<br />
mknod /dev/tty2 c 4 2<br />
mknod /dev/tty3 c 4 3<br />
mknod /dev/tty4 c 4 4<br />
mknod /dev/tty5 c 4 5<br />
mknod /dev/tty6 c 4 6<br />
mknod /dev/tty7 c 4 7<br />
mknod /dev/tty8 c 4 8<br />
mknod /dev/tty9 c 4 9<br />
mknod /dev/tty10 c 4 10<br />
mknod /dev/tty11 c 4 11<br />
mknod /dev/tty12 c 4 12<br />
mknod /dev/ttyS0 c 4 64<br />
mknod /dev/ttyS1 c 4 65<br />
mknod /dev/ttyS2 c 4 66<br />
mknod /dev/ttyS3 c 4 67<br />
echo Setting up hotplug.<br />
hotplug<br />
echo Creating block device nodes.<br />
mkblkdevs<br />
echo "Loading ehci-hcd.ko module"<br />
insmod /lib/ehci-hcd.ko<br />
echo "Loading ohci-hcd.ko module"<br />
insmod /lib/ohci-hcd.ko<br />
echo "Loading uhci-hcd.ko module"<br />
insmod /lib/uhci-hcd.ko<br />
mount -t usbfs /proc/bus/usb /proc/bus/usb<br />
echo "Loading jbd.ko module"<br />
insmod /lib/jbd.ko<br />
echo "Loading ext3.ko module"<br />
insmod /lib/ext3.ko<br />
echo "Loading scsi_mod.ko module"<br />
insmod /lib/scsi_mod.ko<br />
echo "Loading sd_mod.ko module"<br />
insmod /lib/sd_mod.ko<br />
echo "Loading scsi_transport_spi.ko module"<br />
insmod /lib/scsi_transport_spi.ko<br />
echo "Loading mptbase.ko module"<br />
insmod /lib/mptbase.ko<br />
echo "Loading mptscsih.ko module"<br />
insmod /lib/mptscsih.ko<br />
echo "Loading mptspi.ko module"<br />
insmod /lib/mptspi.ko<br />
echo "Loading libata.ko module"<br />
insmod /lib/libata.ko<br />
echo "Loading ata_piix.ko module"<br />
insmod /lib/ata_piix.ko<br />
echo "Loading dm-mem-cache.ko module"<br />
insmod /lib/dm-mem-cache.ko<br />
echo "Loading dm-mod.ko module"<br />
insmod /lib/dm-mod.ko<br />
echo "Loading dm-log.ko module"<br />
insmod /lib/dm-log.ko<br />
echo "Loading dm-region_hash.ko module"<br />
insmod /lib/dm-region_hash.ko<br />
echo "Loading dm-message.ko module"<br />
insmod /lib/dm-message.ko<br />
echo "Loading dm-raid45.ko module"<br />
insmod /lib/dm-raid45.ko<br />
echo Waiting for driver initialization.<br />
stabilized --hash --interval 1000 /proc/scsi/scsi<br />
mkblkdevs<br />
echo Scanning and configuring dmraid supported devices<br />
resume LABEL=SWAP-sda2<br />
echo Creating root device.<br />
mkrootdev -t ext3 -o defaults,ro /dev/sda3<br />
echo Mounting root filesystem.<br />
mount /sysroot<br />
echo Setting up other filesystems.<br />
setuproot<br />
echo Switching to new root and running init.<br />
switchroot<br />
</pre><br />
<br />
=== CentOS 5.7 Boot from USB stick to NFS root ===<br />
<br />
Tree structure:<br />
<pre><br />
|-- bin<br />
| |-- dmraid<br />
| |-- insmod<br />
| |-- kpartx<br />
| |-- modprobe -> /sbin/nash<br />
| `-- nash<br />
|-- dev<br />
| |-- console<br />
| |-- mapper<br />
| |-- null<br />
| |-- ptmx<br />
| |-- ram -> ram1<br />
| |-- ram0<br />
| |-- ram1<br />
| |-- rtc<br />
| |-- systty<br />
| |-- tty<br />
| |-- tty0<br />
| |-- tty1<br />
| |-- tty10<br />
| |-- tty11<br />
| |-- tty12<br />
| |-- tty2<br />
| |-- tty3<br />
| |-- tty4<br />
| |-- tty5<br />
| |-- tty6<br />
| |-- tty7<br />
| |-- tty8<br />
| |-- tty9<br />
| |-- ttyS0<br />
| |-- ttyS1<br />
| |-- ttyS2<br />
| |-- ttyS3<br />
| `-- zero<br />
|-- etc<br />
|-- init<br />
|-- lib<br />
| |-- ata_piix.ko<br />
| |-- dm-log.ko<br />
| |-- dm-mem-cache.ko<br />
| |-- dm-message.ko<br />
| |-- dm-mod.ko<br />
| |-- dm-raid45.ko<br />
| |-- dm-region_hash.ko<br />
| |-- e1000e.ko<br />
| |-- ehci-hcd.ko<br />
| |-- firmware<br />
| |-- libata.ko<br />
| |-- libsas.ko<br />
| |-- lockd.ko<br />
| |-- mvsas.ko<br />
| |-- nfs.ko<br />
| |-- nfs_acl.ko<br />
| |-- ohci-hcd.ko<br />
| |-- pata_marvell.ko<br />
| |-- scsi_mod.ko<br />
| |-- scsi_transport_sas.ko<br />
| |-- sd_mod.ko<br />
| |-- sunrpc.ko<br />
| |-- uhci-hcd.ko<br />
| `-- usb-storage.ko<br />
|-- proc<br />
|-- sbin -> bin<br />
|-- sys<br />
|-- sysroot<br />
`-- var<br />
`-- lib<br />
`-- dhclient<br />
</pre><br />
<br />
initrd<br />
<pre><br />
#!/bin/nash<br />
<br />
mount -t proc /proc /proc<br />
setquiet<br />
echo Mounting proc filesystem<br />
echo Mounting sysfs filesystem<br />
mount -t sysfs /sys /sys<br />
echo Creating /dev<br />
mount -o mode=0755 -t tmpfs /dev /dev<br />
mkdir /dev/pts<br />
mount -t devpts -o gid=5,mode=620 /dev/pts /dev/pts<br />
mkdir /dev/shm<br />
mkdir /dev/mapper<br />
echo Creating initial device nodes<br />
mknod /dev/null c 1 3<br />
mknod /dev/zero c 1 5<br />
mknod /dev/urandom c 1 9<br />
mknod /dev/systty c 4 0<br />
mknod /dev/tty c 5 0<br />
mknod /dev/console c 5 1<br />
mknod /dev/ptmx c 5 2<br />
mknod /dev/rtc c 10 135<br />
mknod /dev/tty0 c 4 0<br />
mknod /dev/tty1 c 4 1<br />
mknod /dev/tty2 c 4 2<br />
mknod /dev/tty3 c 4 3<br />
mknod /dev/tty4 c 4 4<br />
mknod /dev/tty5 c 4 5<br />
mknod /dev/tty6 c 4 6<br />
mknod /dev/tty7 c 4 7<br />
mknod /dev/tty8 c 4 8<br />
mknod /dev/tty9 c 4 9<br />
mknod /dev/tty10 c 4 10<br />
mknod /dev/tty11 c 4 11<br />
mknod /dev/tty12 c 4 12<br />
mknod /dev/ttyS0 c 4 64<br />
mknod /dev/ttyS1 c 4 65<br />
mknod /dev/ttyS2 c 4 66<br />
mknod /dev/ttyS3 c 4 67<br />
echo Setting up hotplug.<br />
hotplug<br />
echo Creating block device nodes.<br />
mkblkdevs<br />
echo "Loading ehci-hcd.ko module"<br />
insmod /lib/ehci-hcd.ko<br />
echo "Loading ohci-hcd.ko module"<br />
insmod /lib/ohci-hcd.ko<br />
echo "Loading uhci-hcd.ko module"<br />
insmod /lib/uhci-hcd.ko<br />
mount -t usbfs /proc/bus/usb /proc/bus/usb<br />
echo "Loading sunrpc.ko module"<br />
insmod /lib/sunrpc.ko<br />
echo "Loading nfs_acl.ko module"<br />
insmod /lib/nfs_acl.ko<br />
echo "Loading lockd.ko module"<br />
insmod /lib/lockd.ko<br />
echo "Loading nfs.ko module"<br />
insmod /lib/nfs.ko<br />
echo "Loading e1000e.ko module"<br />
insmod /lib/e1000e.ko<br />
echo Bringing up eth2<br />
netname 00:1B:21:94:6A:21 eth2<br />
network --device eth2 --bootproto dhcp<br />
rename /var/lib/dhclient/dhclient.leases /var/lib/dhclient/dhclient-eth2.leases<br />
echo "Loading scsi_mod.ko module"<br />
insmod /lib/scsi_mod.ko<br />
echo "Loading sd_mod.ko module"<br />
insmod /lib/sd_mod.ko<br />
echo "Loading scsi_transport_sas.ko module"<br />
insmod /lib/scsi_transport_sas.ko<br />
echo "Loading libata.ko module"<br />
insmod /lib/libata.ko<br />
echo "Loading libsas.ko module"<br />
insmod /lib/libsas.ko<br />
echo "Loading mvsas.ko module"<br />
insmod /lib/mvsas.ko<br />
echo "Loading pata_marvell.ko module"<br />
insmod /lib/pata_marvell.ko<br />
echo "Loading ata_piix.ko module"<br />
insmod /lib/ata_piix.ko<br />
echo "Loading usb-storage.ko module"<br />
insmod /lib/usb-storage.ko<br />
echo Waiting for driver initialization.<br />
stabilized /proc/bus/usb/devices<br />
echo "Loading dm-mem-cache.ko module"<br />
insmod /lib/dm-mem-cache.ko<br />
echo "Loading dm-mod.ko module"<br />
insmod /lib/dm-mod.ko<br />
echo "Loading dm-log.ko module"<br />
insmod /lib/dm-log.ko<br />
echo "Loading dm-region_hash.ko module"<br />
insmod /lib/dm-region_hash.ko<br />
echo "Loading dm-message.ko module"<br />
insmod /lib/dm-message.ko<br />
echo "Loading dm-raid45.ko module"<br />
insmod /lib/dm-raid45.ko<br />
echo Waiting for driver initialization.<br />
stabilized --hash --interval 1000 /proc/scsi/scsi<br />
mkblkdevs<br />
echo Scanning and configuring dmraid supported devices<br />
echo Creating root device.<br />
mkrootdev -t nfs -o rsize=8192,wsize=8192,timeo=14,intr 10.50.8.120:/home/esx/ken/kesx<br />
echo Mounting root filesystem.<br />
mount /sysroot<br />
echo Setting up other filesystems.<br />
setuproot<br />
echo Copying DHCP lease for eth2<br />
cp /var/lib/dhclient/dhclient-eth2.leases /sysroot/dev/.dhclient-eth2.leases<br />
echo Switching to new root and running init.<br />
switchroot<br />
</pre><br />
<br />
== keywords ==<br />
<br />
[[Category:Linux]]</div>
Kenneth