Since Ubuntu 11.04 and Debian wheezy (7.0), Debian and Ubuntu have multiarch support: you can mix x86_32 (i386) and x86_64 (amd64) packages on the same system in a straightforward way. This is known as multiarch support.
In older releases, Debian and Ubuntu ship with a number of 32-bit libraries on amd64. Install the
ia32-libs package to have a basic set of 32-bit libraries, and possibly other packages that depend on this one. Your 32-bit executables should simply run if you have all the required libraries. For development, install
gcc-multilib , and again possibly other packages that depend on it such as
g++-multilib. You may find
binutils-multiarch useful as well, and
ia32-libs-dev on Debian. Pass the
-m32 option to gcc to compile for ix86.
uname -m will still show
x64_64 if you're running a 64-bit kernel, regardless of what 32-bit user mode components you have installed. Schroot described below takes care of this.
This section is a guide to installing a Debian-like distribution “inside” another Linux distribution. It is worded in terms of installing a 32-bit Ubuntu inside a 64-bit Ubuntu, but should apply with minor modifications to other situations, such as installing Debian unstable inside Debian stable or vice versa.
The idea is to install an alternate distribution in a subtree and run from that. You can install a 32-bit system on a 64-bit system that way, or a different release of your distribution, or a testing environment with different sets of packages installed.
chroot command and system call starts a process with a view of the filesystem that's restricted to a subtree of the directory tree. Debian and Ubuntu ship schroot, a utility that wraps around this feature to create a more usable sub-environment.
Set up schroot
This example describes how to set up a 32-bit Ubuntu 10.04LTS (lucid lynx) alternate environment. A similar setup should work with other releases of Debian and Ubuntu. Create a file
/etc/schroot/chroot.d/lucid32 with the following contents:
[lucid32] description=Ubuntu 10.04LTS 32-bit directory=/32 type=directory personality=linux32 users=yourusername groups=users,admin
directory=/32 tells schroot where we'll put the files of the 32-bit installation. The line
username=yourusername says the user
yourusername will be allowed to use the schroot. The line
groups=users,admin says that users in either group will be allowed to use the schroot; you can also put a
Install the new distribution
Create the directory and start populating it with debootstrap. Debootstrap downloads and installs a core set of packages for the specified distribution and architecture.
mkdir /32 debootstrap --arch i386 lucid /32 http://archive.ubuntu.com/ubuntu
You almost have a working system already; what follows is minor enhancements. Schroot automatically overwrites several files in
/32/etc when you run it, in particular the DNS configuration in
/etc/resolv.conf and the user database in
/etc/passwd and other files (this can be overridden, see the documentation). There are a few more files you may want to copy manually once and for all:
cp -p /etc/apt/apt.conf /32/etc/apt/ # for proxy settings cp -p /etc/apt/sources.list /32/etc/apt/ # for universe, security, etc cp -p /etc/environment /32/etc/ # for proxy and locale settings cp -p /etc/sudoers /32/etc/ # for custom sudo settings
There won't be a file
/etc/fstab in the chroot. I don't recommend using the
mount command manually in the chroot, do it from outside. But do create a good-enough
/etc/mtab to make commands such as
df work reasonably.
ln -s /proc/mounts /32/etc/mtab
directory type, schroot will perform bind mounts of a number of directories, i.e. those directories will be shared with the parent installation:
Services in the chroot
As described here, a schroot is not suitable for running daemons. Programs in the schroot will be killed when you exit the schroot. Use a “plain” schroot instead of a “directory” schroot if you want it to be more permanent, and set up permanent bind mounts in
/etc/fstab on the parent installation.
On Debian and Ubuntu, services start automatically on installation. To avoid this (which could disrupt the services running outside the chroot, in particular because network ports are shared), establish a policy of not running services in the chroot. Put the following script as
/32/usr/sbin/policy-rc.d and make it executable (
chmod a+rx /32/usr/sbin/policy-rc.d).
#!/bin/sh ## Don't start any service if running in a chroot. ## See /usr/share/doc/sysv-rc/README.policy-rc.d.gz if [ "$(stat -c %d:%i /)" != "$(stat -c %d:%i /proc/1/root/.)" ]; then exit 101 fi
Populate the new system
Now we can start using the chroot. You'll want to install a few more packages at this point.
schroot -c lucid32 sudo apt-get update apt-get install lsb-core nano ...
You may need to generate a few locales, e.g.
locale-gen en_US en_US.utf8
If the schroot is for an older release of Ubuntu such as 8.04 (hardy), note that the package ubuntu-standard pulls in an MTA. Select
nullmailer instead of the default
postfix (you may want your chroot to send mail but you definitely don't want it to receive any).
Until nex time!
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