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Another FAQ for VServer 2.0

Andreas John's self-FAQ developed from a dialogue with myself and answers from the mailing-list/Bertl

Q: What is a 'Guest'?

A: To talk about stuff, we need some naming. The physical machine is called 'Host' and the 'main' context running the Host Distro is called 'Host Context'. The virtual machine/distro is called 'Guest' and basically is a Distribution (Userspace) running inside a 'Guest Context'.

Q: What kind of Operating System (OS) can I run as guest?

A: With VServer you can only run Linux guests. The trick is that a guest does not run a kernel on its own (as XEN and UML do), it merely uses a virtualized host kernel-interface. VServer offers so called security contexts which make it possible to seperate one guest from each other, i.e. they cannot get data from each other. Imagine it as a chroot environment with much more security and features.

Q: Which distributions did you test?

A: Some. Check out the wiki for ready-made guest images. But you can easily build own guest images, e.g. with Debian's debootstrap. Checkout step-by-step Guide 2.6 how to do that.

Q: Is VServer comparabale to XEN/UML/QEMU?

A: Nope. XEN/UML/QEMU and VServer are just good friends. Because You ask, you probably know what XEN/UML/QEMU is. VServer does in contrary to XEN/UML/QEMU not "emulate" any Hardware you run a kernel on. You can run a VServer kernel in a XEN/UML/QEMU guest. This is confirmed to work at least with linux 2.6/vs2.0.

Q: Is VServer secure?

A: We hope so. It should be as least as secure as Linux is. We consider it much much more secure though.

Q: Performance?

A: For a single guest, we basically have native performance. Some tests showed insignificant overhead (about 1-2%) others ran faster than on an unpatched kernel. This is IMVHO significantly less than other solutions waste, especially if you have more than a single guest (because of the resource sharing).

Q: Is SMP Supported?

A: Yes, on all SMP capable kernel archs.

Q: Resource sharing?

A: Yes ....

Q: Resource limiting?

A: Yes, you can set max limits per guest, but you can only offer guaranteed resource availability with some ticks at the time. There is the possibility to ulimit and to rlimit. rlimit is a new feature of kernel 2.6/vs2.0.

Q: Why isn't there a device /dev/bla? within a guest

A: Device nodes allow Userspace to access hardware (or virtual resources). Creating a device node inside the guest's namespace will give access to that device, so for security reasons, the number of 'given' devices is small.

Q: What is Unification (vunify)?

A: Unification is Hard Links on Steroids. Guests can 'share' common files (usually binaries and libraries) in a secure way, by creating hard links with special properties (immutable but unlinkable (removable)). The tool to identify common files and to unify them is called vunify.

Q: What is vhashify?

A: the successor of vunify, a tool which does unification based on hash values (which allows to find common files in arbitrary pathes)

Q: How do I manage a multi-guest setup with vhashify?

A: -> Enrico ;)

Q: With which VS version should I begin?

A: If you are new to VServer I recommend to try 2.0. Take "aplha utils" Version 0.30.208 and the additional patches for them. In Debian Sid this version is provided as package (but without vhashify as the time).

Q: is there a way to implement "user/group quota" per VServer?

A: Yes, but not on a shared partition for now. You need to put the guest on a separate partition, setup a vroot device (to make the quota access secure), copy that into the guest, and adjust the mtab line inside the guest.

Q: what about "Quota" for a context?

A: context quotas are now called Disk Limits (so that we can tell them apart from the user/group quotas :). they are supported out of the box (with vs2.0) for all major filesystems (ext2/3, reiserfs, xfs, jfs)

Q: Does it support IPv6?

A: Currently not. Some developer has to move his ... to reimplement this functionality from the V4 code (I read that on the ML ;)). Will probably be superseded by the ngnet (next generation networking) soon.

Q: I can't do all I want with the network interfaces inside the guest?

A: For now the networking is 'Host Business'. You can set the capability icmp_raw in the context of the guest, or even the capability CAP_NET_RAW (which would even allow to sniff interfaces of other guests!). Likely to change with ngnet.

'''Q: Is there a web-based interface for vserver? that will allow creation/deletion/configuration etc. of vserver guests?

A. No.

'''Q: What is old-style and new-style config?

A. Old-style config refers to a single text-file that contains all the config. With new-style config the config is split into several directories and files. You should probably go for new-style config if you are asking.

'''Q: What is the "great flower page"?

A. Well, this page contains all config options for vserver in version > 1.9 (I think .. I joined linux-vserver in version 2, so I don't know for sure). The name of the page is derivived from the stylesheet(s) it contains: It displays background pictures of a very great flower, so regard it as highly optimized. It was designed by a non-designer, who asks us to create a better one. I played with the thought of creating a complete theme about [Hommingberger-Gepardenforelle] for that page - but actually we all got used to the name "great flower page", so we stick to it. If you are unable to read it clearly, feel invited to joim the IRC channel #vserver, we may tell you how to ;)

'''Q: How do I add may IPs to a vserver?

A: First of all a guest only supports up to 16 IP (There is a 64-IP patch available, which is in "derjohn's kernel", you need extra util-vserver anyway).

Here is a little helper-script that adds a list of IPs defined in a text file, one per line.

#!/bin/bash
j=1
for i in `cat myiplist`; do
        j=$(($j+1))
        mkdir $j
        echo $i > $j/ip
        echo $i > $j/ip-old
        echo "24" > $j/prefix
done

'''Q: If my host has only one public IP, can I use RFC1918 IP (e.g. 192.168.foo.bar) for the guests?

A: Yes, use iptables with SNAT to masquerade it. The parameters are: -j SNAT --to <public-ip>.

Example command lines - explained:

$ foo
bar ....