N3vlr-rootfs

How to create a mini rootfilesystem starting from a N3VLR image

Installation

Download N3VLR image from http://www.n3network.ch/resources/n3vlr/n3vlr-0.11-uml.tar.bz2

Extract the rootfs image:

tar xvfj n3vlr-0.11-uml.tar.bz2

Copy the original rootfs image to a new file and mount it :

cp n3vlr-0.11-uml.img n3vlr-0.11-vnuml.img
mount -o loop n3vlr-0.11-vnuml.img /mnt/

Create vnuml directories and umlboot link:

mkdir /mnt/mnt/vnuml
mkdir /mnt/mnt/hostfs
ln -s /mnt/vnuml/umlboot /mnt/etc/init.d/S40bootuml
echo "/dev/ubdb     /mnt/vnuml iso9660     defaults    0 0" >> /mnt/etc/fstab

Change the content of /mnt/etc/inittab to:

::sysinit:/etc/init.d/rcS
tty0::respawn:/sbin/getty 38400 tty0
tty1::respawn:/sbin/getty 38400 tty1
tty2::respawn:/sbin/getty 38400 tty2
::ctrlaltdel:/sbin/halt

Create the /dev/ubd[a-h] nodes using the makeUBDdev.sh script (see the complete script below taken from http://www.theshore.net/~caker/uml/)

cd /mnt/dev
makeUBDdev.sh

Change root password:

chroot /mnt /bin/ash
passwd root
  (set password to xxxx)
exit

Edit the file /mnt/etc/ssh/sshd_config in order to make it work with ssh v1:

# What ports, IPs and protocols we listen for
Port 22
Protocol 2,1
# HostKeys for protocol version 1
HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes
# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768
# Logging
SyslogFacility AUTH
LogLevel INFO
# Authentication:
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
UsePAM yes

Install bash shell in mini rootfs:

1. Download from http://downloads.openwrt.org/kamikaze/7.09/x86-2.6/ the file openwrt-x86-2.6-ext2.fs and mount in ~/tmp ,for example.
2. Download from http://downloads.openwrt.org/kamikaze/packages/i386/ the package bash_3.2-1_i386.ipk
3. Do

chroot ~/tmp /bin/ash
ipkg install bash_3.2-1_i386.ipk
exit
cp ~/tmp/bin/bash /mnt/bin/
cp ~/tmp/lib/libgcc_s.so.1 /mnt/lib
umount ~/tmp

Change the content of /mnt/etc/passwd to:

root:$1$Yq7hudHO$r1rNwGNrK1470rWb5Qwu51:0:0:root:/tmp:/bin/bash
nobody:*:65534:65534:nobody:/var:/bin/false
sshd:x:99:99:sshd:/var/empty/.sshd:/bin/false
quagga:x:100:100:quagga:/var/empty/.quagga:/bin/false

Unmount the filesystem:

umount /mnt

Notes:

1. To use this mini rootfs, you must have the patch that includes the change of command line and the order cad.(patch)
2. Shell. You have to force the shell to be used by vnuml in the virtual machine to /bin/bash with: <shell>/bin/sh</shell>
3. The directory of demons is usr/sbin/. You can try this mini rootfs with these examples:
   1. Example-OSPF (ospf_lab.xml, ospf_lab_tiny.xml, ospf_lab_conf.tar)

makeUBDdev.sh script

---

#!/bin/bash
device=ubd
major=98
minor=0
for u in a b c d e f g h
        do dev=$device$u
       
        mknod $dev b $major $minor
        chmod 660 $dev
        chgrp disk $dev
       
        for i in $(seq 1 15)
                do 
                mknod $dev$i b $major $(($minor + $i)) 
                chmod 660 $dev$i
                chgrp disk $dev$i
        done
        minor=$(($minor + 16))
done

References

http://wiki.n3network.ch/index.php/N3_Virtual_Linux_Router

http://openwrt.org/