TITLE: Bootable LFS CD using lilo LFS VERSION: LFS 4.0 onwards AUTHOR: Chris Lingard chris@stockwith.co.uk CREDITS Thanks to Gerard Beekmans, Martin L. Pursche and many others` LINKS: My boot disk www.stockwith.co.uk The package www.stockwith.uklinux.net Please do not use this until after I have upgraded it. Problems with ISP, since I took hosting away from them. SYNOPSIS: This hint involves using two LFS systems to build a third system on a CD. It does not use any external packages, the boot method being LFS Index 1. Introduction 2. How it boots 3. What it boots 3. The base system 4. The image system 5. Making the package 6. Building the image 7. Some uses for the boot CD HINT: 1. Introduction This is my method of making a bootable CD I started this project when I realised that I had no proper recovery system, and it just grew from there. I tried various other systems; the best being cd_template by Martin L. Pursche. Extending this package, to boot a full Linux system, became my goal. Here are the standard warnings. You must be confident enough to build systems, with various hacks and modifications. You must be careful enough to avoid wrecking your systems; many of the scripts will mess up your base system if run wrongly. 2. How it boots First a few words on how to make a bootable CD, (using lilo). When you burn a CD using mkisofs, you have the -b option to specify the boot image. This boot image must be something that the hardware understands, therefore you need to emulate a floppy. Since we are only pretending that is a floppy, we may choose any type, so we choose the largest -- a 2.88Mb floppy. We make a file using a loop device that is exactly 2.88Mb, copy files to it, then run lilo on it. Please note that it is the BIOS that reads this 2.88Mb image. Once this is read, then BIOS/lilo gives control to the kernel. The kernel boots, decompresses the initrd file, and mounts this as the root file system. We need to run lilo on the 2.88Mb file. Here is a lilo.conf: cat > $TOPDIR/lilo.conf << EOF disk=/dev/loop1 bios=0x00 # bios ID from drive A, we need that here because lilo # need to know which boot device to use sectors=36 # 2.88MB disk geometry heads=2 cylinders=80 timeout=30 lba32 boot=/dev/loop1 message=/mnt/loop1/boot.msg install=/mnt/loop1/boot.b map=/mnt/loop1/map prompt image=/mnt/loop1/vmlinuz label=linux initrd=/mnt/loop1/initrd.gz append = "root=/dev/ram0 init=/linuxrc rw" ramdisk=$ISIZE EOF # run lilo /sbin/lilo -C $TOPDIR/lilo.conf At the start of the above, you can see us telling lies to the hardware, that this is a 2.88Mb floppy. We have put a kernel and boot message into this file system. The initrd.gz is a compressed file system. linuxrc is an executable script in the root of this file system. This must all fit inside 2.88Mb. The initrd file system may be 6.5Mb, before compression, and still be small enough. linuxrc may be a symbolic link to bash 3. What it boots The files in the base of this file are: boot-menu.b boot.b boot.msg initrd.gz map vmlinuz boot.b is a symbolic link to boot-menu.b, and these together with map are copied from /boot on your base system boot.msg is a text file that gives the start of boot greeting vmlinux is the kernel, and initrd.gz is a compressed file system that will become the root partition. The file system may contain anything you like, but this is all you will have after booting the CD You can make this system inside a directory; it will look something like: /dev # Use devfsd /bin -> sbin /lib # Needed if you are using dynamic programs /lib/modules # See next paragraph` /linuxrc # The script /sbin # You selection of programs The directory modules should be copied from your target system. These will be the modules available during the boot. Once the boot is complete then /lib/modules will be available from your target system via the CD. Once you have made this; you calculate its size, make a file system on loop device, copy the files, then compress it into initrd.gz. During the linuxrc script you would mount the cdrom, giving you access to whatever you put on the CD. See the mount_cdrom script below that auto-detects the cdrom, and modify it to do what you want. 4. The base system The base system's kernel will need loop devices enabled. I use mkisofs and cdrecord from package cdrtools. You will also need directories for the loop back devices to use; /mnt/loop1 and /mnt/loop2 are what I use. 5. The image system This system must be running devfsd, as this is used for hardware detection You should implement the pciutils package to get the lspci program. You must decide if you just want a CD that will work on your machine, (and any identical); or you want a CD that will work on any PC. If you want a generic CD, then you must build a generic system to act as the image; follow the cross compile hint to build a generic 486 LFS system. The system used for the image can be any working combination you choose. Things that use many shared libraries, such as KDE, should be avoided, because they will be too slow for any effective work on a CD. I use a standard LFS plus a few extras such as gpm, X and lynx. If you really want a large KDE type system, then get the cloop daemon from Knoppix. This allows you to make and mount compressed partitions. The kernel of the booting system must have been built with: CONFIG_BLK_DEV_RAM_SIZE=32768 6. Making the package You will need two LFS systems to generate a bootable CD. One is the base system that will be used for building. The other is the system that provides the image. Here is how it works. Let us first consider what we want. We need a writable root partition, so we will make one out of RAM. We will want /proc and /cdrom mounted on the root. We also want /root and /etc writeable, so these are unpacked from tar files during the boot process. (How the image system is prepared is described later). The start up linuxrc will achieve this, then pass control to init. Here is my linuxrc script: #!/bin/sh /sbin/devfsd /dev mount -t proc none /proc modprobe -q -s `cat /scsi` dd if=/dev/zero of=/dev/ram2 bs=1k count=25000 mkdir -p ram mke2fs -q /dev/ram2 mount /dev/ram2 /ram cd /ram mkdir cdrom /mount_cdrom mkdir proc mount -t proc none /ram/proc cdrom/bin/ln -s cdrom/bin bin bin/ln -s cdrom/sbin sbin bin/ln -s cdrom/lib lib bin/ln -s cdrom/boot boot bin/ln -s /cdrom/usr usr dd if=/dev/zero of=swapspace bs=1k count=5000 sbin/mkswap swapspace bin/echo "Preparing file systems for pivot" mkdir home mkdir dev mkdir tmp mkdir mnt mkdir mnt/lfs mkdir var cd var mkdir lib lock log mail run spool tmp opt cache lib/misc local cd /ram bin/echo "Unpacking tar files for /etc and /root" bin/tar xf /ram/cdrom/etc.tar bin/tar xf /ram/cdrom/root.tar mkdir initrd sbin/pivot_root . initrd # Get devices on the new root /bin/killall devfsd mount devfs -t devfs /dev exec /usr/sbin/chroot . /sbin/init dev/console 2>&1 The only non standard thing used here is mount_cdrom, this is it. #!/bin/sh for disk in 0 1 2 3 4 5 6 7; do if mount -t iso9660 -o ro -n /dev/cdroms/cdrom$disk /ram/cdrom 2> /dev/null ; then if [ -r /ram/cdrom/LFS-4.1 ]; then echo "Found the CD-ROM" exit else umount /ram/cdrom; fi; fi done echo "No CD-ROM found" The file LFS-4.1 is to make sure tha the right CD is mounted. The file scsi is a list of scsi modules like: 3w-xxxx 53c7,8xx AM53C974 BusLogic ....... ....... Each is loaded in turn in case the machine has this scsi driver. From this is can be seen that the following programs are needed during the boot process: bash chroot devfsd insmod ksyms mkdir modprobe pivot_root sh cat dd echo kallsyms lsmod mke2fs mount rmmod umount (kallsyms, ksyms, lsmod, modprobe and rmmod are symbolic links to insmod) (sh is a symbolic link to bash) Because shared libraries plus programs are smaller than static programs, the following libraries are needed: ld-2.3.1.so ld-linux.so.2 -> ld-2.3.1.so libc-2.3.1.so libc.so.6 -> libc-2.3.1.so libcom_err.so.2 -> libcom_err.so.2.0 libcom_err.so.2.0 libdl-2.3.1.so libdl.so.2 -> libdl-2.3.1.so libe2p.so.2 -> libe2p.so.2.3 libe2p.so.2.3 libext2fs.so.2 -> libext2fs.so.2.4 libext2fs.so.2.4 libuuid.so.1 -> libuuid.so.1.2 libuuid.so.1.2 We can therefore make a system like this in a directory called initrdtree ls initrdtree/ bin dev etc initrd lib linuxrc mount_cdrom proc root sbin tmp usr var Where bin a link to sbin, sbin contains the programs and lib the libraries. linuxrc and mount_cdrom are the scripts, and dev has the devices. This file system must be small enough, ( 6-7Mb ), so that its compressed size, plus a kernel is less than 2.88Mb. A file system can be made on a loop device, and the directory initrdtree copied to it. The file system is then compressed. This put into a futher file system containing a kernel. This file system must be exactly 2.88Mb, (it is a floppy to the hardware). This is also mounted on a loop device and lilo is run on it. This is then the boot image that mkisofs sees with the -b flag The build directory looks like: bootimagetree # Contains the kernel and the compressed file system build.sh # The script initrdtree # Contains the boot image system before compression cdtree # The system providing the CD image is mounted here Here is the script build.sh that builds the iso; note that the system providing the CD image is mounted on cdtree/ #! /bin/sh if [ -z $TOPDIR ] ; then echo "you must define TOPDIR" exit fi oldpwd=`pwd` cd $TOPDIR # we need to set aside a few loop devices. I chose (in reverse order of their appearance) # -- loop1 for the boot image # -- loop2 for the ram disk image # since the loop1 choice is reflected in the lilo.loopfix file, # you should not change that (or you need to change the file). # I had used loop0 first, but I found that this is used by the Samba daemon. # Also, I assume that the mount points are /mnt/loop{1,2}. # In principle we could do with one, but it comes in handy to be able to # leave one mounted, so I took two different ones. # we first assume that a proper directory tree of the later ramdisk # is in the initrdtree directory. Put everything in there what you think # will be needed. We assume that this is the case. echo -n "Creating the Initial Ramdisk image.... " # first find out how much space we need. ISIZE=`du -s -k $TOPDIR/initrdtree/ | awk '{print $1}'` # is that true? Anyway, we are smaller than that. if [ $ISIZE -gt 8192 ]; then echo "Initial Ramdisk max size exceeded ($ISIZE, max is 8192KB)" exit 1 fi ISIZE=`expr $ISIZE + 1024` ISIZE=8192 echo "Initial Ramdisk contents will be $ISIZE KB" # delete the existing ramdisk image, if there is one rm -f $TOPDIR/ramdisk # create a file of $ISIZE Kb dd if=/dev/zero of=$TOPDIR/ramdisk bs=1k count=$ISIZE # associate it with /dev/loop2 losetup /dev/loop2 $TOPDIR/ramdisk # make an ext2 filesystem on it. We set the amount of unused space to 0% # and turn down the number of inodes to save space #mkfs -t ext2 -i 16384 -m 0 /dev/loop2 mke2fs -F -m0 -b 1024 /dev/loop2 # we mount it... mount /dev/loop2 /mnt/loop2 # ... and delete the lost+found directory rm -rf /mnt/loop2/lost+found # then we copy the contents of our initrdtree to this filesystem cp -dpR $TOPDIR/initrdtree/* /mnt/loop2/ # and unmount and divorce /dev/loop2 umount /mnt/loop2 losetup -d /dev/loop2 echo "done" # Now we have the image of the ramdisk in $TOPDIR/ramdisk. We # compress this one and write the compressed image to the boot tree: echo -n "Compressing the Ramdisk image.... " # delete any existing one rm -f $TOPDIR/bootimagetree/initrd.* # and gzip our ramdisk image and put it in the right place. gzip -9 -c $TOPDIR/ramdisk > $TOPDIR/bootimagetree/initrd.gz # we are done with the uncompressed ramdisk image, delete it rm $TOPDIR/ramdisk # how much is the contents of the bootimagetree? ISIZE=`du -s -k $TOPDIR/bootimagetree/ | awk '{print $1}'` echo "Boot image size is $ISIZE KB" echo "done" # Part II. We work the boot tree (with the image of the ramdisk) now. # we put that into yet another image which we put on the CD. # This image has to be 2.88 MB exactly, because we emulate a 2.88MB floppy. echo -n "Creating the boot image.... " # delete any leftover version rm -f $TOPDIR/cdtree/Boot.img # and make a file of the proper size (this time it's fixed at 2880 KB) # note that the file gets created already in the right place to be the boot image. dd if=/dev/zero of=$TOPDIR/cdtree/Boot.img bs=1k count=2880 # this one gets associated with loop1 and gets a ext2 file system losetup /dev/loop1 $TOPDIR/cdtree/Boot.img mke2fs -F -m0 -b 1024 /dev/loop1 # mount it... mount /dev/loop1 /mnt/loop1 rm -rf /mnt/loop1/lost+found # ... and copy the contents of our bootimagetree over cp -dpR $TOPDIR/bootimagetree/* /mnt/loop1/ # now we calculate the ramdisk size for the lilo.conf # Hard code the size we want; also see linuxrc for dd's count= ISIZE=30000 echo "Ram disk size will be $ISIZE KB" cat > $TOPDIR/lilo.conf < fstab << EOF /dev/ram2 / ext2 defaults 0 0 proc /proc proc defaults 0 0 /swapspace swap swap defaults 0 0 EOF You need the script checkcd to replace checkfs and mountfs cat > $LFS/etc/rc.d/init.d/checkcd << EOF #!/bin/sh # Begin /etc/rc.d/init.d/checkcd # # Include the functions declared in the /etc/rc.d/init.d/functions file # source /etc/rc.d/init.d/functions # # Activate all the swap partitions declared in the /etc/fstab file # echo -n "Activating swap..." /sbin/swapon -a evaluate_retval echo -n "Remounting root file system in read-write mode..." /bin/mount -n -o remount,rw / evaluate_retval echo "Making /tmp writeable" chmod 1777 /tmp umount /initrd/proc umount /initrd/dev echo "Goodbye to the RAMDISK" umount /initrd EOF Note that the umount of /initrd releases the boot image, it is no longer needed. You need the Detect script cat > $LFS/etc/rc.d/init.d/Detect << EOF #!/bin/bash # Begin $rc_base/init.d/ # Based on sysklogd script from LFS-3.1 and earlier. # Rewritten by Gerard Beekmans - gerard@linuxfromscratch.org source /etc/sysconfig/rc source $rc_functions case "$1" in start) echo "Starting hardare detection" /sbin/lspci -v >& /tmp/t if grep OHCI /tmp/t >& /dev/null; then modprobe -a usb-ohci; modprobe -a hid; fi rm /tmp/t loadproc /sbin/Opendirs if [ -c /dev/input/mouse0 ]; then ln -s /dev/input/mouse0 /dev/mouse; else if [ -c /dev/misc/psaux ]; then ln -s /dev/misc/psaux /dev/mouse; fi fi evaluate_retval ;; stop) echo "Stopping..." killproc ;; reload) echo "Reloading..." reloadproc ;; restart) $0 stop sleep 1 $0 start ;; status) statusproc ;; *) echo "Usage: $0 {start|stop|reload|restart|status}" exit 1 ;; esac # End $rc_base/init.d/ And here is the source of the Opendirs program, (please do not laugh) #include #include #include #include int main(void) { char CD[12] = "/dev/cdroms"; char IDEHD[12] = "/dev/discs"; char FLOPPY[12] = "/dev/floppy"; char SCSIHD[12] = "/dev/scsi"; char USB[12] = "/dev/usb"; DIR *D; printf("Detecting CDs\n"); D = opendir(CD); closedir(D); printf("Detecting IDE HDs\n"); D = opendir(IDEHD); closedir(D); printf("Detecting floppy\n"); D = opendir(FLOPPY); closedir(D); printf("Detecting SCSI HDs\n"); D = opendir(SCSIHD); closedir(D); printf("Detecting USB\n"); D = opendir(USB); closedir(D); exit(0); } We need to disable some of the target system's start up scripts. cd $LFS/etc/rc.d/rcsysinit.d mv S10swap ZZZS10swap mv S20mountproc ZZZS20mountproc mv S30checkfs ZZZS30checkfs mv S40mountfs ZZZS40mountfs Check that your $LFS/etc/inittab will start up at level 3 Inspect your level 3 start up scripts and disable any that you think are inappropriate. Add the following links: ln -s ../init.d/checkcd S35checkcd ln -s ../init.d/Detect S40Detect You need to tar $LFS/root and $LFS/etc cd $LFS tar cf root.tar root tar cf etc.tar etc Finally you need to put a marker file LFS-4.1 in the root; so that the boot mechanism chooses the right CD. touch $LFS/LFS-4.1 7. Building the image Return to the build directory and set TOPDIR cd where_ever_it_is/cd_builder export TOPDIR=`pwd` The directory cdtree must have the LFS root directory mounted. On my system it is /dev/hdb6 so: mount /dev/hdb6 cdtree If you have a separate partition for usr then mount this too mount /dev/hdxx cdtree/usr If you have a partition containing source you may also mount this. Mine is /dev/hdb5 so: mount /dev/hdb5 cdtree/usr/src You can now build the image: bash build.sh >& Build & Check the output for any warning or any "file system full". A warning from lilo about lilo.conf not having the correct permissions is normal; the latest lilo will also warn about lba32 and compact. If you have both the LFS and the LFS/usr/src mounted the image in bootcd.iso will be about 300Mb. Write this to a CD and try the system. Restoration of the LFS system There are two changes to be made before the image LFS system will reboot: $LFS/etc/fstab $LFS/etc/rc.d/rcsysinit.d The fstab cd $LFS/etc cp fstab fstab.cd cp fstab.bak fstab The links cd $LFS/etc/rc.d/rcsysinit.d mv ZZZS10swap S10swap mv ZZZS20mountproc S20mountproc mv ZZZS30checkfs S30checkfs mv ZZZS40mountfs S40mountfs cd ../rc3.d mv S35checkcd ZZZS35checkcd mv S40Detect ZZZS40Detect Your LFS system should now boot; enabling you to change and tune it. Then add more software before building a better CD. 7. Some uses for the boot CD Broken files Any partition can be mounted; files edited or replaced by those on the CD. Mending a broken lilo Suppose that the machine just does LILILILI on boot up. Boot from the CD and mount your root partition to /disk; if your not sure which partition; then test the partitions listed in /proc/partition until you get the right one. Once you have the broken root partition mounted do: chroot /disk export PATH=/bin:/sbin:/usr/bin:/usr/sbin cd /etc vi lilo.conf and fix what is wrong then lilo -C lilo.conf Exit (from the chroot), unmount the disk and reboot. What I have is an automated build of LFS on my CD. I build LFS systems onto empty machines.