bsd.m3th.org
Yet another *nix admin blog

I had migrated some of the old machines at work to Xen hypervisor VM. The procedure is rather straight forward and with many options. In this post, I used simple dd command to migrate physical machine to a flat file image on Xen server.

DD IN ACTION

debian-HP370:~/ # dd if=/dev/cciss/c0d0 | ssh me@xenserver cat ‘>’/home/xen/img/debian-HP370.img

This will take a long time depending on your disk size/network speed. So leave it there and go on with other stuff. After a couple of hours, you have the image transferred to Xen server.

TAILORING TO VM ENVIRONMENT

As the physical machine has smart array raid and VM has choices of disk options: IDE, SATA, physical partition under the VM guest, I mounted the image and edit /etc/fstab to reflect disk on VM. Mounting an image file with many partitions is simple. Firstly, offset value of the partition is required. This can be obtained via fdisk command.

xenserver:/home/xen/img # fdisk -lu debian-HP370.img
You must set cylinders.
You can do this from the extra functions menu.

Disk debian-HP370.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0×111f5759

Device Boot Start End Blocks Id System
debian-HP370.imgp1 * 63 102269789 51134863+ 83 Linux
debian-HP370.imgp2 102269790 106655534 2192872+ 5 Extended
debian-HP370.imgp5 102269853 106655534 2192841 82 Linux swap / Solaris

The offset value in this example is 63 * 512 = 32256

Note : 63 is the Start sector of the partition that I wanted to mount.

xenserver:/home/xen/img # mount -o loop,offset=32256 debian-HP370.img /mnt/stuff

Next, you can just vi /mnt/stuff/etc/fstab, to suit your Xen VM configurations. We are almost done.

CREATING NEW VM

Creating a new VM is rather easy. You need a configuration file for VM guest. Please refer to example and wiki for complete parameters. Just run xm new <configure file> i.e. xm new debian-vmconfig or else use vm-install and be prompted with bunch of questions for configuration parameters. Sample HVM configuration file for my VM:-

name=”Linux-debian-HP370″
memory=1024
maxmem=2048
vcpus=2
on_poweroff=”destroy”
on_reboot=”restart”
on_crash=”destroy”
localtime=0
keymap=”en-us”

builder=”hvm”
extid=0
device_model=”/usr/lib/xen/bin/qemu-dm”
kernel=”/usr/lib/xen/boot/hvmloader”
boot=”c”
disk=[ 'file:/home/xen/img/debian-HP370.img,sda,w', ]
vif=[ 'mac=00:16:3e:51:16:ee,bridge=br0,model=e1000', ]

stdvga=0
vnc=1
vncunused=1
apic=1
acpi=1
pae=1

serial=”pty”

START THE MACHINE, LITERALLY

At this point of time, you should turn off the physical machine to avoid IP address clash. There is one last step to go which is the editing grub on VM. You could just fire up the new guest VM with xm start Linux-debian-HP370 && xm console Linux-debian-HP370 and hit “e” at GRUB menu to edit kernel parameter for root disk. Lastly, modify /boot/grub/menu.lst to reflect your root partition. Remember to run update-grub after finished editing.

OPTIONAL

Since my xen is a headless box, I have to go extra mile to get into the console by ssh tunnel.

ssh me@xenserver -L 5900:127.0.0.1:5900

Connect vnc to localhost will give you the new shinny VM console.

The link aggregation and link failover interface, lagg(4) device, first appeared in FreeBSD 6.3. It as the name suggested allows aggregation of multiple network interfaces as one virtual lagg(4) interface for the purpose of providing fault-tolerance and high-speed links. The driver currently supports the aggregation protocols such as failover, fec, lacp, loadbalance, roundrobin, and none by detecting child interface link state.

This is useful in large enterprise environment. Nonetheless, you can use it to set up roaming between wired and wireless network. The lagg(4) manpage provides simple example. However, it states that

WPA security does not currently work correctly with a wireless interface added to the lagg port.

Well, it is easy to overcome the issue by use of wpa_supplicant(8). Just set up /etc/wpa_supplicant.conf as normal. Please refer to wpa_supplicant.conf manpage for detailed setup. Here is my example.

/etc/wpa_supplicant.conf :-

ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=wheel
ap_scan=1
network={
       ssid="MY_WPA_WIFI"
       scan_ssid=1
       key_mgmt=WPA-PSK
       psk="verysecretpassword"
}

/etc/rc.conf :-

ifconfig_nfe0="DHCP"
ifconfig_ndis0="WPA DHCP"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggproto failover laggport ndis0 laggport nfe0 DHCP"

Relevant ifconfig output :-

ndis0: flags=8843 metric 0 mtu 1500
        ether 00:1a:73:73:92:34
        media: IEEE 802.11 Wireless Ethernet autoselect
        status: associated
        ssid "MY_WPA_WIFI" channel 1 (2412 Mhz 11b)
        authmode OPEN privacy OFF bmiss 7 scanvalid 60 roaming MANUAL
        bintval 0
        lagg: laggdev lagg0
nfe0: flags=8843 metric 0 mtu 1500
        options=8
        ether 00:1a:73:73:92:34
        media: Ethernet autoselect (none)
        status: no carrier
        lagg: laggdev lagg0
lagg0: flags=8843 metric 0 mtu 1500
        ether 00:1a:73:73:92:34
        inet 192.168.1.5 netmask 0xffffff00 broadcast 192.168.1.255
        media: Ethernet autoselect
        status: active
        laggproto failover
        laggport: nfe0 flags=0<>
        laggport: ndis0 flags=5
tun0: flags=8010 metric 0 mtu 1500

It is that easy. Your laptop will auto roam between wired and wireless connection.