Initramfs¶

/init

#!/bin/busybox sh

# Mount the /proc and /sys filesystems.
mount -t proc none /proc
mount -t sysfs none /sys

# Do your stuff here.
echo "This script mounts rootfs and boots it up, nothing more!" 

rescue_shell() {
    echo "Something went wrong. Dropping you to a shell." 
    busybox --install -s
    exec /bin/sh
}

mini_udev() {
    ln -s ../bin/busybox /sbin/mdev
    echo /sbin/mdev > /proc/sys/kernel/hotplug
    /sbin/mdev -s
}

# Use devtmpfs if possible
if grep -qs devtmpfs /proc/filesystems; then
    mount -n -t devtmpfs -o "exec,nosuid,mode=0755,size=10M" udev /dev
    devtmpfs=true
else    
    mini_udev
    devtmpfs=false
fi

uuidlabel_root() {
    for cmd in $(cat /proc/cmdline) ; do
        case $cmd in
        root=*)

        mkdir -p /etc/lvm
        echo 'devices { filter = [ "a|/dev/md[0-9]+$|", "a|/dev/[hsv]d[a-z][0-9]*$|", "r/.*/" ] }' > /etc/lvm/lvm.conf

        echo 'activation { udev_rules = 0 }' >> /etc/lvm/lvm.conf

        /sbin/lvm vgscan
        /sbin/lvm vgchange -ay --sysinit

            type=$(echo $cmd | cut -d= -f2)
            if [ $type == "LABEL" ] || [ $type == "UUID" ] ; then
                uuid=$(echo $cmd | cut -d= -f3)
                mount -o ro $(blkid |grep "$type=\"$uuid\"" | cut -d: -f1 | grep -v '/dev/dm-[0-9]*$\|-real$' | sort | head -n1 ) /mnt/root || rescue_shell
            else
                mount -o ro $(echo $cmd | cut -d= -f2) /mnt/root || rescue_shell
            fi
            ;;
    rescue)
        rescue_shell
        ;;
        esac
    done
}

uuidlabel_root || rescue_shell

# Remount /dev if devtmpfs
$devtmpfs && mount -n --move /dev /mnt/root/dev

# Clean up.
umount /proc
umount /sys

# Boot the real thing.
exec switch_root /mnt/root /sbin/init

Вариант с gzip¶

cd initramfs
find | cpio -o -H newc | gzip -9 > ../initramfs-2012-04-03.igz

Вариант с xz¶

cd initramfs
find | cpio -o -H newc | xz -v --check=crc32 --x86 --lzma2 > ../initramfs-2015-04-03.ixz

для сборки i686:

/etc/paludis/bashrc

CC="x86_64-pc-linux-gnu-gcc -m32" 

для dropbear --enable-static-nss (glibc)

/etc/paludis/use.conf.d/initramfs.conf

dev-libs/libtommath static-libs
net-misc/dropbear minimal -pam -shadow static -zlib
dev-libs/popt static-libs
net-misc/rsync static -drop_cache -iconv -ipv6
sys-fs/lvm2 static -udev
sys-apps/busybox -ipv6 static

Конвертируем ключи openssh в ключи для dropbear¶

dropbearconvert openssh dropbear ../ssh/ssh_host_rsa_key dropbear_rsa_host_key
dropbearconvert openssh dropbear ../ssh/ssh_host_dsa_key dropbear_dsa_host_key
dropbearconvert openssh dropbear ../ssh/ssh_host_ecdsa_key dropbear_ecdsa_host_key