A few weeks back, I installed a vanilla Debian Wheezy on an OVH’s Kimsufi. OVH is a large web hosting company that provides dedicated servers called Kimsufis. This explains how to proceed using debootstrap and then setting up Xen for virtualization.
These are some preliminary examinations, you can jump straight to the next part to get your hands dirty.
There are some ways I’ve thought to install Debian Wheezy on a Kimsufi:
via the manager (“Wheezy ALPHA” being available now): I’m not sure if we can make our very own custom partitioning keeping some existing data. Moreover, your distro will be tainted with OVH’s stuff like RTM and their SSH keys. → Nah.
via qemu: the plan would be to download the latest Wheezy ISO and boot it on qemu with VNC enabled. But this would install Debian over emulated hardware which is no good. → Messy.
via rescue mode: OVH provides what they call a “rescue mode” which boots on a live CD giving you access to your server hard drive. So the plan is to
/dev/sda, set up minimal functioning network and sshd then reboot on the real system. → Sounds good to me :).
Why and why not using a custom kernel.
- Does Debian’s stock kernel support OVH hardware? Probably. Is it optimized for their hardware? Unlikely.
- Debian’s kernel includes a lots of exotic hardware support – both as
- OVH’s kernel disables all useless stuff like Bluetooth, WiFi, touchscreen and so on
- why not
- What about kernel updates?
OVH’s kernels are static, i.e. no
Why no PV
- Requires Wheezy (Linux >= 3) or patched kernel – current Lenny VMs must be upgraded.
- Sharing kernels on the dom0 is annoying.
- 2-partition scheme seems to be mandatory? Does it work with block partitions like
- HVM full isolation is better since it gives total freedom to guests who want to run BSD, etc.
If you’ve got existing data, backup them all before going any further – just in case.
You can use OVH’s FTP if 100 Gio is enough for you or use
rsync to backup things locally.
If you have running VMs (“domU” in Xen wording), don’t forget to shut them gracefully with
xm shutdown <ID>.
Then enable the “rescue mode” in the manager and reboot your server.
Once you got the prompt on the live CD, you can start the fresh install. Here are the steps I used but YMMV :).
$ mkfs.ext3 /dev/sda1 $ mkfs.ext4 /dev/sda2 $ mount /dev/sda2 /mnt $ mkdir /mnt/boot $ mount /dev/sda1 /mnt/boot $ debootstrap --verbose --arch amd64 --variant minbase --include dialog,vim,resolvconf,ifupdown,netbase,net-tools,ssh wheezy /mnt http://mir1.ovh.net/debian $ cat > /mnt/etc/fstab <<CONF # <file system> <mount point> <type> <options> <dump> <pass> /dev/sda1 /boot ext3 errors=remount-ro 0 1 /dev/sda2 / ext4 errors=remount-ro 0 1 /dev/sda3 swap swap defaults 0 0 /dev/sda5 /srv ext3 errors=remount-ro 0 1 proc /proc proc defaults 0 0 sysfs /sys sysfs defaults 0 0 CONF $ cat > /mnt/etc/network/interfaces <<CONF # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 188.165.X.Y netmask 255.255.255.0 gateway 188.165.X.254 dns-nameservers 220.127.116.11 # FIXME: IPv6 support CONF $ cat > /mnt/etc/hosts <<CONF 127.0.0.1 localhost.localdomain localhost 188.165.X.Y ks123456.kimsufi.com ks123456 # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts CONF $ echo 'ks123456' > /mnt/etc/hostname $ cat > /mnt/etc/apt/sources.list <<CONF deb http://mir1.ovh.net/debian wheezy main deb http://security.debian.org/ wheezy/updates main CONF $ vim /mnt/etc/ssh/sshd_config # `PermitRootLogin yes` should be there $ echo "root:super_password" | chroot /mnt chpasswd $ mount --rbind /dev /mnt/dev $ LANG=C chroot /mnt /bin/bash # from inside chroot $ mount -a $ dpkg-reconfigure tzdata # 13 (Etc) then 33 (UTC) $ apt-get update $ apt-cache search linux-image $ apt-get install linux-image $ apt-get install grub $ grub-install --no-floppy --recheck /dev/sda $ update-grub $ ls /boot/grub/grub.cfg # should be happy
Finally! Now disable the “rescue mode” then reboot.
If you’re stuck with Grub rescue prompt (it happened to me on a test machine but not the actual Kimsufi), type in
configfile /boot/grub/grub.cfg and reinstall Grub once booted.
Install the hypervisor and tools
To get Xen support, simply install those three packages (xen-hypervisor provides
apt-get install xen-hypervisor xen-tools xen-utils
Prioritize the Xen kernel over native (more info):
dpkg-divert --divert /etc/grub.d/08_linux_xen --rename /etc/grub.d/20_linux_xen update-grub
Xen toolstacks, in short:
- Old toolstack: xm based on xend
- New one: xl based on libxl
- New bloated one: xe based on xapi
You may want to look at this comparison.
xl and not
xe/xapi seemed neat, especially the RRD bit which provides nice graphs about your VMs. But xapi requires openvswitch. When I tried to install it, apt-get was stuck in an infinite loop because of a missing kernel module :/. Besides, openvswitch helps with things like QoS – iptables’ limit module already does that.
It bloats your distro because it launches at least three more daemons, needs custom kernel modules, relies on some experimental Java stuff. All that to provide things like QoS that I either can do using iptables or that I don’t need.
Apparently, you can tell xapi to use Linux bridging capability instead of OVS but it doesn’t work either for me since I’ll need to use routing and not bridging to set up the network. ebtables is fine but it’s not as powerful as iptables to do amazing things and fine-tuning (see below).
And for the graphs, I guess it’s possible to retrieve data from xl and send it through Munin to get some nice graphs…
“xl is very lightweight and is a great choice for developers or users who are most comfortable with Unix like CLI tools.” – Choice of Toolstacks
Here we go! One thing though: Python support has been dropped from xm – annoying but not a big deal.
How to set the toolstack
/etc/default/xen and set
TOOLSTACK=xl then reboot.
xend will not start any more (see
/etc/init.d/xen for more info).
dom0 important tweaking
Disable Xen ballooning & set dom0 dedicated RAM
free -m to see how much RAM you’re using and set a fair amount of dedicated memory by adding the two lines into
# Xen boot parameters for all Xen boots GRUB_CMDLINE_XEN="dom0_mem=256M,max:256M"
After reboot, you may blurt out a little “dafuq” seeing this:
free -mreports 176M
xl list 0reports 256M
This is fine – well, sort of – the missing memory seems to be marked as “reserved” according to
Then disable auto ballooning in
(dom0-min-mem 256) (enable-dom0-ballooning no)
Disable domU save/restore
Unless you have room to save VMs states, disable it in
Enough CPU time
Add these two lines into
/etc/rc.local (more info):
# Give dom0 two times more CPU time than guests xl sched-credit -d Domain-0 -w 512
Xen is now all set up, you need to
update-grub then reboot to apply all the changes!
Here is a example config file to get you started with a HVM guest:
hostname = "test" kernel = "hvmloader" device_model = "qemu-dm" builder = "hvm" boot = "c" memory = "1024" vcpus = "2" disk = ["phy:/dev/sda6,xvda,w"] pae = "1" apic = "1" on_poweroff = "destroy" on_crash = "restart" on_reboot = "restart"
What about VMs’ networking? This will be discussed in another post – how to set up a routed network with Xen 4 using a dual-stack IPv4 and IPv6.