In the past, I’ve described how one could build multiarch (64 bit and 32 bit) versions of R on a 64 bit Ubuntu machine. The method based on this thread no longer works as of R 2.13 or 2.14 I believe. I received advice from someone on #R over on freenode (forgot who) a few months ago that suggested the chroot route (see this also). I recently tried it and wanted to document the procedures. Although the solution isn’t as nice as the previous multiarch route, it will suffice for now. With the chroot method, first compile the 64 bit version of R the usual way. For the 32 bit version of R, do:

#### change my.username to your username, or modify path per your taste
### create chroot jail
sudo apt-get install dchroot debootstrap
sudo mkdir ~/chroot-R32
sudo emacs -q -nw /etc/schroot/schroot.conf
## paste the following in the file: (no quotes)
"
[natty]
description=Ubuntu Natty
location=/home/my.username/chroot-R32
priority=3
users=my.username
groups=sbuild
root-groups=root
"

## build a basic Ubuntu system in the chroot jail
sudo debootstrap --variant=buildd --arch i386 natty /home/my.username/chroot-R32 http://ubuntu.cs.utah.edu/ubuntu/ ## pick a mirror from https://launchpad.net/ubuntu/+archivemirrors

## copy my source locations for apt
sudo cp /etc/apt/sources.list /var/chroot/etc/apt/sources.list ## edit this new file if to reflect only the needed source

### do following steps whenever you need to access 32 bit R
## access to proc and dns
sudo mount -o bind /proc /home/my.username/chroot-R32/proc
sudo cp /etc/resolv.conf /home/my.username/chroot-R32/etc/resolv.conf
## go into jail; do this whenever you want
sudo chroot /home/my.username/chroot-R32
dpkg-architecture ## make sure system is i386
### now the root / location should reflect the jail

### following happens in jail
## tools needed to build R
apt-get install gcc g++ gfortran libreadline-dev libx11-dev xorg-dev
## get svn to get latest r source code
apt-get install git-core subversion

## compile 32 bit R
cd home/
mkdir R32
cd R32
svn checkout https://svn.r-project.org/R/trunk/ r-devel
cd r-devel/
apt-get install rsync
./tools/rsync-recommended 
./configure
make
make install
R

How big is my /home/my.username/chroot-R32 folder? It is at 791 MB after the above steps. Let me know if you have suggestions for having both 32 bit or 64 concurrently on Linux. I believe Windows and Mac ships and compiles both 32 bit and 64 bit versions of R. I’m surprised this isn’t the case for Linux.