8.1. Building the ISO live system

As we want to put a whole system on little space, we will squash some directories to have some more free space on the cd or dvd. +

+ Before squashing, we have some work to do +

Issue the following:

cd $LFSMOUNT

As the system won't be writable, we have to provide a directory that will be mounted on tmpfs and will, therefore, be writable to ensure a successful boot.

mkdir -v ro rw dev

Make sure you have support for loopback device in your kernel:

ls -l /dev | grep loop

You should see a few /dev/loopX, where X is a number from 0 to 7. If this is not the case, and the loopback is supported as a kernel module, try to modprobe the module and retry again:

modprobe loop
+ls -l /dev | grep loop

Create some essential files in the dev directory

mknod -m 600 dev/console c 5 1
+mknod -m 666 dev/null c 1 3
+cp -av /dev/loop[0-7] dev/
+mknod dev/ram0 b 1 0

Copy the /etc directory

cp -av /etc .

Modify some files in it

echo "" > etc/mtab
+cat > etc/fstab << "EOF"
+# Begin /etc/fstab
+
+# file system  	mount-point             type    options         	dump  fsck
+#                                                        		      order
+
+proc            /proc                   proc    defaults                0       0
+sysfs           /sys                    sysfs   defaults                0       0
+devpts          /dev/pts                devpts  gid=4,mode=620          0       0
+tmpfs           /run                    tmpfs   defaults                0       0
+usbfs           /proc/bus/usb           usbfs   devgid=14,devmode=0660  0       0
+
+# End /etc/fstab
+EOF

While booting, we will have to copy some directories in shared memory, and mount a root filesystem on it. This has to be done in the first bootscript.

8.1.1. Creating bootscript

issue the following to create a new bootscript:

cd etc/rc.d/init.d
+cat > mountrootfs << "EOF"
+#!/bin/sh
+
+# Set up variables
+
+dir_rw=/rw
+dir_ro=/ro
+
+# Source functions
+
+source /etc/rc.d/init.d/functions
+
+case "$1" in
+  start)
+          
+# Mount temporary files on $dir_rw
+
+    echo "Mounting tmpfs on $dir_rw..."
+    mount -t tmpfs tmpfs $dir_rw
+    evaluate_retval
+    sleep 1
+    
+# Create essential dirs in dir_rw
+
+    mkdir $dir_rw/{dev,etc,home,media,mnt}
+    mkdir $dir_rw/{opt,root,srv,tmp,usr,var}
+
+# If you have some other dirs in $LFSMOUNT/ like sources
+# Add them to that list, eg: mkdir -v $dir_rw/sources
+    
+mount -n -t squashfs root.sqsh ro -o loop
+mount -n -t aufs -o dirs=$dir_rw/etc=rw:$dir_ro/etc=ro aufs etc
+mount -n -t aufs -o dirs=$dir_rw/usr=rw:$dir_ro/usr=ro aufs usr
+mount -n -t aufs -o dirs=$dir_rw/tmp=rw:$dir_ro/tmp=ro aufs tmp
+mount -n -t aufs -o dirs=$dir_rw/var=rw:$dir_ro/var=ro aufs var
+mount -n -t aufs -o dirs=$dir_rw/dev=rw:$dir_ro/dev=ro aufs dev
+mount -n -t aufs -o dirs=$dir_rw/home=rw:$dir_ro/home=ro aufs home
+mount -n -t aufs -o dirs=$dir_rw/media=rw:$dir_ro/media=ro aufs media
+mount -n -t aufs -o dirs=$dir_rw/mnt=rw:$dir_ro/mnt=ro aufs mnt
+mount -n -t aufs -o dirs=$dir_rw/opt=rw:$dir_ro/opt=ro aufs opt
+mount -n -t aufs -o dirs=$dir_rw/root=rw:$dir_ro/root=ro aufs root
+mount -n -t aufs -o dirs=$dir_rw/srv=rw:$dir_ro/srv=ro aufs srv
+chmod 1777 /tmp
+         
+  ;;
+  *)
+    echo "Usage: $0 {start}"
+    exit 1
+  ;;
+esac
+EOF
+chmod 0754 mountrootfs

Inspect the contents of etc/rc.d/rcS.d

ls -l ../rcS.d

You should see a list beginning with S00mountvirtfs, S02consolelog, ...

Now, issue:

cd ../rcS.d
+mv -v S00mountvirtfs S01mountvirtfs
+ln -sv ../init.d/mountrootfs S00mountrootfs
+

The live system can not be checked with fsck so remove these bootscripts

rm S30checkfs
+rm S40mountfs
+rm S45cleanfs
+

8.1.2. About the var directory

As we are just copying our system, we will need the var directory while booting. We have to remove pid and sockets file from it.

cd $LFSMOUNT
+cp -av /var .
+cd var
+rm log/*.log
+for FILE in `find . -type f -name '*pid'`
+  do rm $FILE
+done
+for FILE in `find . -type s`
+  do rm $FILE
+done
+rm -rf tmp/*
+cd $LFSMOUNT

8.1.3. Squashing directories

Create tmp, root and other directories, then squash all. When squashing, you might not want to add some file or directory. Add files to the -e option of mksquashfs if you wish.

mkdir -pv home media mnt opt proc root run srv sys tmp usr ro/{dev,etc,home,media,mnt,opt,root,srv,tmp,usr,var}
+mksquashfs dev etc /home /media mnt /opt /root /srv tmp /usr var root.sqsh -keep-as-directory -info
+rm -r var/*
+

Copy dirs that won't be squashed:

cp -av /bin /boot /lib /sbin .

Copy our previous created initrd.gz to /boot of the media.

cp <PATH-TO-INITRD>/initrd.gz $LFSMOUNT/boot

LFS live howto - Version 0.3

Chapter 8. Building the ISO live system

8.1. Building the ISO live system

8.1.1. Creating bootscript

8.1.2. About the var directory

8.1.3. Squashing directories