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How to create a User-Mode-Linux Debian root-file-system for VNX

Follow this procedure to create a UML Debian Squeeze (6.0) root filesystem for VNX.

Basic installation and configuration

  • Requirements:
  • apt-get install debootstrap
  • Create and format the file that will host the filesystem:
  • dd bs=1M if=/dev/zero of=vnx_rootfs_uml_debian.img count=2048
    mkfs.ext4 vnx_rootfs_uml_debian.img 
  • Mount it and and use debootstrap to populate it:
  • mkdir mnt
    mount -o loop vnx_rootfs_uml_debian.img mnt/
    debootstrap --arch i386 squeeze mnt/

    Note: change to the mirror nearest you (e.g.

  • Chroot to the new filesystem to continue the installation:
  • mount -t proc none mnt/proc
    chroot mnt
    env -update
    ln -sf /usr/share/zoneinfo/Europe/Madrid /etc/localtime 
  • Install the packages desired. For example, for a root filesystem mainly used in networking laboratories:
  • apt-get install locales aptsh file less perl-modules vim openssh-server    \
       openssh-client telnet sudo lsof ssh ncurses-term bzip2 strace   \
       tcpdump tshark apache2 apache2-utils dnsutils finger ftp ftpd   \
       ipsec-tools iputils-tracepath ipv6calc ipvsadm lpr lynx         \
       nfs-common openssl pidentd portmap ppp procmail python          \
       python-central python-newt quagga racoon radvd  sharutils squid \
       squid-common ssl-cert vlan whois iptables bind9
    sudo dpkg-reconfigure locales
  • Stop and disable startup of services installed:
  • /etc/init.d/apache2 stop
    /etc/init.d/squid stop
    /etc/init.d/bind9 stop
    /etc/init.d/exim4 stop
    /etc/init.d/lpd stop
    update-rc.d -f apache2 remove
    update-rc.d -f squid remove
    update-rc.d -f bind9 remove
    update-rc.d -f exim4 remove
    update-rc.d -f lpd remove
  • Set locales according to your language:
  • export LANGUAGE=es_ES.ISO-8859-1
    export LANG=es_ES.ISO-8859-1
    export LC_ALL=es_ES.ISO-8859-1
    locale-gen es_ES.ISO-8859-1
    apt-get install locales
    dpkg-reconfigure locales
  • Clean apt cache:
  • apt-get clean
  • Set hostname:
  • echo vnx > /etc/hostname
  • Set consoles and loopback network interface configuration:
  • echo '0:2345:respawn:/sbin/getty 38400 tty0' >> /etc/inittab
    echo 'tty0' >> /etc/securetty 
    echo 'ssh' >> /etc/securetty
    echo 'auto lo' >> /etc/network/interfaces
    echo 'iface lo inet loopback' >> /etc/network/interfaces
  • Configure /etc/fstab:
  • echo 'proc         /proc          proc     defaults   0 0' >> /etc/fstab
    echo 'devpts       /dev/pts       devpts   mode=0622  0 0' >> /etc/fstab
    echo '/dev/ubda    /              ext4     defaults   0 1' >> /etc/fstab
    echo '/dev/ubdb    /mnt/vnuml     iso9660  defaults   0 0' >> /etc/fstab
  • Set root password:
  • passwd
  • Change /etc/inittab to halt on CAD signal:
  • # What to do when CTRL-ALT-DEL is pressed.
    ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -h now
  • Create VNX specific directories:
  • mkdir /mnt/vnuml
    mkdir /mnt/hostfs
  • Create file /etc/init.d/vnxboot:
  • #! /bin/sh
    # Provides:          vnxboot
    # Required-Start:    $remote_fs $syslog $all
    # Required-Stop:
    # Default-Start:     2
    # Default-Stop:
    # Short-Description: Run /mnt/vnuml/umlboot if it exist
    . /lib/init/
    . /lib/lsb/init-functions
    do_start() {
    	if [ -x /mnt/vnuml/umlboot ]; then
    	        [ "$VERBOSE" != no ] && log_begin_msg "Running vnxboot (/mnt/vnuml/umlboot)"
    		[ "$VERBOSE" != no ] && log_end_msg $ES
    		return $ES
    case "$1" in
            echo "Error: argument '$1' not supported" >&2
            exit 3
            echo "Usage: $0 start|stop" >&2
            exit 3
  • Give it execution permissions and enable it at startup:
  • chmod +x /etc/init.d/vnxboot
    cd /etc/rc2.d
    ln -s ../init.d/vnxboot S11vnxboot
    update-rc.d vnxboot enable
  • Create the /usr/local/bin/vnx_halt script:
  • #!/bin/bash
    if [ "$1" == '-y' ]; then
    # Clean apt cache
    apt-get clean
    apt-get -y autoremove
    # Delete /etc/resolv.conf
    rm -f /etc/resolv.conf
    # Clean command history
    rm -f /root/.bash_history
    # Delete udev net rules files:
    rm -f /etc/udev/rules.d/70-persistent-net.rules
    if [ ! $NOINTMODE ]; then
        while true; do
            # Ask for a message to save in /etc/vnx_rootfs_version file
            echo    "** Save a log message in /etc/vnx_rootfs_version file "
            echo -n "** describing the modifications done? "
            read -n 1 -p "[y/n] " answer
            echo ""
            case $answer in
                [Yy]* )
                        echo "** Log message (1 line maximum):"
                        read logmsg
                        echo "MODDATE=$DATE" >> /etc/vnx_rootfs_version
                        echo "MODDESC=$logmsg" >> /etc/vnx_rootfs_version
                [Nn]* ) break;;
                * )     echo "** Error: please answer 'y' or 'n'.";;
    # Check whether we are running chrooted or not
    if [ ! -e /proc/1/root ]; then
      # Probably running chrooted. Do not halt!
      echo "**"
      echo "** Cannot read /proc. Probably running chrooted. Not halting"
      echo "** Type 'exit' to exit from chroot"
    elif [ ! -e /proc/1/root -o "$(stat -c %d:%i /)" != "$(stat -c %d:%i /proc/1/root/.)" ]; then
      # We are chrooted! Do not halt
      echo "**"
      echo "** Running chrooted. Not halting"
      echo "** Type 'exit' to exit from chroot"
    # We are NOT chrooted! We halt the virtual machine
    halt -p
  • Give it execution permissions:
  • chmod +x /usr/local/bin/vnx_halt
  • Create a file /etc/vnx_rootfs_version to store version number and informacion about modifications:
  • VER=v0.24
    OS=Debian Squeeze (6.0)
    DESC=Debian Squeeze root-file-system without GUI
  • Create /dev/ubd* devices:
  • cd /dev
    mknod --mode=660 ubda b 98 0
    mknod --mode=660 ubdb b 98 0
    chown root:disk ubda        
    chown root:disk ubdb
  • Clean caches and history files and optionally leave a description message /etc/vnx_rootfs_version file:
  • vnx_halt
  • Exit chroot: exit
  • Install kernel modules:
  • cd mnt/lib/modules/
    tar xfv /usr/share/vnx/kernels/linux-3.3.8-um-src/modules-3.3.8.tar 
    cd ../../../
  • Umount rootfs to finish installation:
  • umount mnt/proc/
    umount mnt

    Note: if you cannot umount 'mnt' directory, check which process is blocking the unmounting operation with 'lsof mnt' and stop it.


Install VNXACED if you plan to use command execution based on 'sdisk' mode:

  • Mount the rootfs:
  • mount -o loop vnx_rootfs_uml_debian-6.0-v024c.img /mnt
  • Copy vnxaced tar file:
  • cp /usr/share/vnx/aced/vnx-aced-lf-2.0b.2487.tgz /mnt/tmp
  • chroot to rootfs and install:
  • chroot /mnt
    apt-get -y install libxml-libxml-perl
    cd /tmp
    tar xfvz vnx-aced-lf-2.0b.2487.tgz
    LC_ALL=C perl vnx-aced-lf-2.0b.2487/install_vnxaced
    cd /mnt 
    ln -s hostfs sdisk
  • Edit /usr/local/bin/vnxaced and change:
  • use constant H2VM_CHANNEL => 'SERIAL';
    use constant MOUNT => 'YES';


    use constant H2VM_CHANNEL => 'SHARED_FILE';
    use constant MOUNT => 'NO';
  • Finish:
  • exit
    umount /mnt

Installing additional software

There is two basic ways to update a UML root filesystems:

A. Starting a virtual machine that mounts the rootfs in direct mode:

  • Create a VNX scenario named, for example, update_uml.xml (available in /usr/share/vnx/examples):
  • <?xml version="1.0" encoding="UTF-8"?>
    VNX Sample scenarios
    Name:        update_uml
    Description: Simple scenario to start a uml virtual machine in direct mode to make modifications 
                 in a filesystem. Tha VM is connected to virbr0, the default network used by libvirt, 
                 to gain network connectivity.
    This file is part of the Virtual Networks over LinuX (VNX) Project distribution. 
    (www: - e-mail: 
    Departamento de Ingenieria de Sistemas Telematicos (DIT)
    Universidad Politecnica de Madrid
    <vnx xmlns:xsi=""
        <vm_mgmt type="none" />
            <exec_mode type="uml">mconsole</exec_mode>
      <net name="virbr0" mode="virtual_bridge" />
      <vm name="uml" type="uml" subtype="" os="">
        <filesystem type="direct">ROOTFS_PATHNAME</filesystem>
        <kernel trace="on">UML_KERNEL</kernel>
        <console id="0" display="yes">xterm</console>
        <if id="1" net="virbr0">
        <exec seq="on_boot" type="verbatim">dhclient eth1</exec>

    Change ROOTFS_PATHNAME and UML_KERNEL by the full pathname of the root filesystem to be modified and the UML kernel to be used to start it.

  • Start the virtual machine with:
  • vnx -f update_uml.xml -v -t
  • Once started, check that the virtual machine has network connectivity. If not, try to configure it with:
  • dhclient eth1
  • Do the installations or modifications desired
  • Finally, clean caches and history files and, optionally, leave a message describing the modifications done (saved to /etc/vnx_rootfs_version file), befor halting the virtual machine:
  • vnx_halt

B. Mounting the rootfs and chrooting to it:

  • Mount the rootfs:
  • mkdir mnt
    mount -o loop vnx_rootfs_uml_debian.img mnt/
    mount -t proc none mnt/proc
  • Chroot:
  • chroot mnt
    env -update
  • Check you have network connectivity. You'll probably have to modify /etc/resolv.conf file to configure DNS server IP address
  • Modify the rootfs
  • Clean caches and history files and optionally leave a message describing the modifications done (saved to /etc/vnx_rootfs_version file:
  • vnx_halt
  • Exit chroot an umount:
  • exit
    umount mnt/proc
    umount mnt

    Note: if you cannot umount 'mnt' directory, check which process is blocking the unmounting operation with 'lsof mnt' and stop it.

Installing kernel modules

When you change or update the kernel you are using with a root filesystem, you have to copy the new kernel modules to the root filesystem:

mount -o loop vnx_rootfs_uml_debian.img mnt
cd mnt/lib/modules/
tar xfv /usr/share/vnx/kernels/linux-3.3.8-um-src/modules-3.3.8.tar 
cd ../../../ 
umount mnt/