%general-entities; ]> $LastChangedBy$ $Date$ The only purpose of an initramfs is to mount the root filesystem. The initramfs is a complete set of directories that you would find on a normal root filesystem. It is bundled into a single cpio archive and compressed with one of several compression algorithms. At boot time, the boot loader loads the kernel and the initramfs image into memory and starts the kernel. The kernel checks for the presence of the initramfs and, if found, mounts it as / and runs /init. The init program is typically a shell script. Note that the boot process takes longer, possibly significantly longer, if an initramfs is used. For most distributions, kernel modules are the biggest reason to have an initramfs. In a general distribution, there are many unknowns such as file system types and disk layouts. In a way, this is the opposite of LFS where the system capabilities and layout are known and a custom kernel is normally built. In this situation, an initramfs is rarely needed. There are only four primary reasons to have an initramfs in the LFS environment: loading the rootfs from a network, loading it from an LVM logical volume, having an encrypted rootfs where a password is required, or for the convenience of specifying the rootfs as a LABEL or UUID. Anything else usually means that the kernel was not configured properly. If you do decide to build an initramfs, the following scripts will provide a basis to do it. The scripts will allow specifying a rootfs via partition UUID or partition LABEL or a rootfs on an LVM logical volume. They do not support an encrypted root file system or mounting the rootfs over a network card. For a more complete capability see the LFS Hints or dracut. To install these scripts, run the following commands as the root user: cat > /sbin/mkinitramfs << "EOF" #!/bin/bash # This file based in part on the mkinitrafms script for the LFS LiveCD # written by Alexander E. Patrakov and Jeremy Huntwork. copy() { local file if [ "$2" == "lib" ]; then file=$(PATH=/lib:/usr/lib type -p $1) else file=$(type -p $1) fi if [ -n $file ] ; then cp $file $WDIR/$2 else echo "Missing required file: $1 for directory $2" rm -rf $WDIR exit 1 fi } if [ -z $1 ] ; then INITRAMFS_FILE=initrd.img-no-kmods else KERNEL_VERSION=$1 INITRAMFS_FILE=initrd.img-$KERNEL_VERSION fi if [ -n "$KERNEL_VERSION" ] && [ ! -d "/lib/modules/$1" ] ; then echo "No modules directory named $1" exit 1 fi printf "Creating $INITRAMFS_FILE... " binfiles="sh cat cp dd killall ls lsmod mkdir mknod mount " binfiles="$binfiles umount sed sleep ln rm uname" sbinfiles="udevadm udevd modprobe blkid switch_root mdadm" unsorted=$(mktemp /tmp/unsorted.XXXXXXXXXX) DATADIR=/usr/share/mkinitramfs INITIN=init.in # Create a temporrary working directory WDIR=$(mktemp -d /tmp/initrd-work.XXXXXXXXXX) # Create base directory structure mkdir -p $WDIR/{bin,dev,lib/firmware,run,sbin,sys,proc} mkdir -p $WDIR/etc/{modprobe.d,udev/rules.d} touch $WDIR/etc/modprobe.d/modprobe.conf ln -s lib $WDIR/lib64 # Create necessary device nodes mknod -m 640 $WDIR/dev/console c 5 1 mknod -m 664 $WDIR/dev/null c 1 3 # Install the udev configuration files cp /etc/udev/udev.conf $WDIR/etc/udev/udev.conf for file in $(find /etc/udev/rules.d/ -type f) ; do cp $file $WDIR/etc/udev/rules.d done if [ -f /etc/mdadm.conf ] ; then cp /etc/mdadm.conf $WDIR/etc fi # Install the init file install -m0755 $DATADIR/$INITIN $WDIR/init if [ -n "$KERNEL_VERSION" ] ; then if [ -x /bin/kmod ] ; then binfiles="$binfiles kmod" else binfiles="$binfiles lsmod" sbinfiles="$sbinfiles insmod" fi fi # Install basic binaries for f in $binfiles ; do ldd /bin/$f | sed "s/\t//" | cut -d " " -f1 >> $unsorted copy $f bin done # Add lvm if present if [ -x /sbin/lvm ] ; then sbinfiles="$sbinfiles lvm"; fi for f in $sbinfiles ; do ldd /sbin/$f | sed "s/\t//" | cut -d " " -f1 >> $unsorted copy $f sbin done # Add module symlinks if appropriate if [ -n "$KERNEL_VERSION" ] && [ -x /bin/kmod ] ; then ln -s kmod $WDIR/bin/lsmod ln -s kmod $WDIR/bin/insmod fi # Add lvm symlinks if appropriate if [ -x /sbin/lvm ] ; then ln -s lvm $WDIR/sbin/lvchange ln -s lvm $WDIR/sbin/lvchange ln -s lvm $WDIR/sbin/lvchange ln -s lvm $WDIR/sbin/lvcreate ln -s lvm $WDIR/sbin/lvdisplay ln -s lvm $WDIR/sbin/lvscan ln -s lvm $WDIR/sbin/pvchange ln -s lvm $WDIR/sbin/pvck ln -s lvm $WDIR/sbin/pvcreate ln -s lvm $WDIR/sbin/pvdisplay ln -s lvm $WDIR/sbin/pvscan ln -s lvm $WDIR/sbin/vgcreate ln -s lvm $WDIR/sbin/vgscan ln -s lvm $WDIR/sbin/vgrename ln -s lvm $WDIR/sbin/vgck fi # Install libraries sort $unsorted | uniq | while read lib ; do if [ "$lib" == "linux-vdso.so.1" ] || [ "$lib" == "linux-gate.so.1" ]; then continue fi copy $library lib done cp -a /lib/udev $WDIR/lib # Install the kernel modules if requested if [ -n "$KERNEL_VERSION" ]; then find \ /lib/modules/$KERNEL_VERSION/kernel/{crypto,fs,lib} \ /lib/modules/$KERNEL_VERSION/kernel/drivers/{block,ata,md,firewire} \ /lib/modules/$KERNEL_VERSION/kernel/drivers/{scsi,message,pcmcia,virtio} \ /lib/modules/$KERNEL_VERSION/kernel/drivers/usb/{host,storage} \ -type f 2> /dev/null | cpio --make-directories -p --quiet $WDIR depmod -b $WDIR $KERNEL_VERSION fi ( cd $WDIR ; find . | cpio -o -H newc --quiet | gzip -9 ) > $INITRAMFS_FILE # Remove the temporary directory and file rm -rf $WDIR $unsorted printf "done.\n" EOF mkdir -p /usr/share/mkinitramfs && cat > /usr/share/mkinitramfs/init.in << "EOF" #!/bin/sh PATH=/bin:/usr/bin:/sbin:/usr/sbin export PATH problem() { printf "Encountered a problem!\n\nDropping you to a shell.\n\n" sh } no_device() { printf "The device %s, which is supposed to contain the\n" $1 printf "root file system, does not exist.\n" printf "Please fix this problem and exit this shell.\n\n" } no_mount() { printf "Could not mount device %s\n" $1 printf "Sleeping forever. Please reboot and fix the kernel command line.\n\n" printf "Maybe the device is formatted with an unsupported file system?\n\n" printf "Or maybe filesystem type autodetection went wrong, in which case\n" printf "you should add the rootfstype=... parameter to the kernel command line.\n\n" printf "Available partitions:\n" } do_mount_root() { mkdir /.root [ -n "$rootflags" ] && rootflags="$rootflags," rootflags="$rootflags$ro" case "$root" in /dev/* ) device=$root ;; UUID=* ) eval $root; device="/dev/disk/by-uuid/$UUID" ;; LABEL=*) eval $root; device="/dev/disk/by-uuid/$LABEL" ;; "" ) echo "No root device specified." ; problem ;; esac while [ ! -b "$device" ] ; do no_device $device problem done if ! mount -n -t "$rootfstype" -o "$rootflags" "$device" /.root ; then no_mount $device cat /proc/partitions while true ; do sleep 10000 ; done else echo "Successfully mounted device $root" fi } init=/sbin/init root= rootdelay= rootfstype=auto ro="ro" rootflags= device= mount -n -t devtmpfs devtmpfs /dev mknod -m 640 /dev/console c 5 1 mknod -m 664 /dev/null c 1 3 mount -n -t proc proc /proc mount -n -t sysfs sysfs /sys mount -n -t tmpfs tmpfs /run read -r cmdline < /proc/cmdline for param in $cmdline ; do case $param in init=* ) init=${param#init=} ;; root=* ) root=${param#root=} ;; rootdelay=* ) rootdelay=${param#rootdelay=} ;; rootfstype=*) rootfstype=${param#rootfstype=} ;; rootflags=* ) rootflags=${param#rootflags=} ;; ro ) ro="ro" ;; rw ) ro="rw" ;; esac done udevd --daemon --resolve-names=never udevadm trigger udevadm settle if [ -f /etc/mdadm.conf ] ; then mdadm -As ; fi if [ -x /sbin/vgchange ] ; then /sbin/vgchange -a y > /dev/null ; fi if [ -n "$rootdelay" ] ; then sleep "$rootdelay" ; fi do_mount_root killall -w /sbin/udevd exec switch_root /.root "$init" "$@" EOF Required Runtime Dependency User Notes: To build an initramfs, run the following as the root user: mkinitramfs [KERNEL VERSION] The optional argument is the directory where the appropriate kernel modules are located. This must be a subdirectory of /lib/modules. If no modules are specified, then the initramfs is named initrd.img-no-kmods. If a kernel version is specified, the initrd is named initrd.img-$KERNEL_VERSION and is only appropriate for the specific kernel specified. The output file will be placed in the current directory. After generating the initrd, copy it to the /boot directory. Now edit /boot/grub/grub.cfg and add a new menuentry. Below are several examples. # Generic initramfs and root fs identified by UUID menuentry "LFS Dev (LFS-7.0-Feb14) initrd, Linux 3.0.4" { linux /vmlinuz-3.0.4-lfs-20120214 root=UUID=54b934a9-302d-415e-ac11-4988408eb0a8 ro initrd /initrd.img-no-kmods } # Generic initramfs and root fs on LVM partition menuentry "LFS Dev (LFS-7.0-Feb18) initrd lvm, Linux 3.0.4" { linux /vmlinuz-3.0.4-lfs-20120218 root=/dev/mapper/myroot ro initrd /initrd.img-no-kmods } # Specific initramfs and root fs identified by LABEL menuentry "LFS Dev (LFS-7.1-Feb20) initrd label, Linux 3.2.6" { linux /vmlinuz-3.2.6-lfs71-120220 root=LABEL=lfs71 ro initrd /initrd.img-3.2.6-lfs71-120220 } Finally, reboot the system and select the desired system.