32-bit Chroot

The 1.3-release of Funtoo Linux deprecates support for 32-bit applications and libraries on x86-64bit arch via 'multilib' -- for more information see this forums post. This page provides background for this decision as well as steps that can be used to provide 32-bit support without multilib, namely a 32-bit chroot.

Background

The x86 Instruction Set Architecture includes 64-bit registers which have been implemented in processors from AMD, Intel and others starting in 2003 (AMD Opteron).

Since then most new and existing applications have been written to make use of x86-64bit architecture. Fewer applications require 32-bit support. In the past, x86-64bit arch on Funtoo Linux has provided support for 64 and 32-bit applications and libraries simultaneously -- called 'multilib' -- which is a capability that is part of the GNU C library and dynamic library loader.

However, multilib support makes ebuild maintenance more complex, and we have had 64-bit instructions for 15+ years, and fewer and fewer things truly need 32-bit support. Therefore it makes sense to start to transition to a pure 64-bit non-multilib environment to reduce the complexity of ebuilds, and look at other approaches to solve the 32-bit compatibility problem.

Options

Users needing to run 32-bit programs on x86-64bit hardware have several options:

1. install a second separate instance of Funtoo Linux using x86-32bit arch builds.
2. install an x86-32bit arch instance of Funtoo Linux on an x86-64bit host. Users then chroot into the 32-bit chroot environment using the linux32 (i.e. setarch) command provided by No results. This guide will detail the setup and use of this second scenario.
3. use LXD to set up a 32-bit container.

See Chroot and Containers for a full list of options documented on the wiki.

Installation

This guide describes a 32-bit chroot installed into a new directory on existing storage.

user $ su -
Password:
root # mkdir -p /path/to/chroot/directory
root # cd /path/to/chroot/directory

Similar to a Funtoo installation an appropriate Stage3 tarball must be downloaded and extracted. This will provide the directories, files and links necessary for the 32-bit chroot.

Please refer to the Subarches page for an appropriate 32-bit Stage3. The following x86-32bit builds would be appropriate on an x86-64bit host

Subarch	CPU Family
Generic 32	32-bit Processors (PC-Compatible, Generic)
I686	32-bit Processors (PC-Compatible, Generic)
Atom 32	32-bit Intel Processors
Pentium4	32-bit Intel Processors

You should choose a 32-bit subarch with features and CPU_FLAGS that are compatible with the subarch and CPU of your x86-64bit host. If in doubt, choose 'Generic 32'.

Copy the download link address for the 1.3-release-std build and paste it into your terminal to download using wget.

root # wget https://build.funtoo.org/1.3-release-std/x86-32bit/generic_32/2018-12-13/stage3-generic_32-1.3-release-std-2018-12-13.tar.xz

From within your 32-bit chroot directory, run the following command to extract the Stage3 tarball, preserving permissions:

root # tar -xpf stage3-generic_32-1.3-release-std-2018-12-13.tar.xz

Instead of having duplicate portage trees, this 32-bit chroot will instead use the meta-repo of the 64-bit host. To further eliminate duplicate downloads you can also use the local Portage sourcefile directory on the host inside of the chroot (see 'DISTDIR' in emerge --info). Package source files already fetched by the host will then be available for use by Portage inside of the chroot.

To achieve this you must first create the necessary directories inside of the 32-bit chroot folder. Later the host folders will bind-mount onto these empty directories.

root # mkdir -p var/git/meta-repo
root # mkdir -p var/cache/portage/distfiles

sys-apps/portage and other packages must only see the environment variables of the 32-bit chroot and not those of the 64-bit host. The Gentoo guide requires users to execute env-update each time you enter the 32-bit chroot environment. The following configuration will set this to occur automatically.

Create and edit the file .bash_profile inside of the directory /part/to/chroot/directory/root/ to include the following

root # nano root/.bash_profile

   .bash_profile - /root/.bash_profile inside of /path/to/chroot/directory/

#run env-update on 32-bit chroot login
env-update

As the last step you should configure app-shells/bash to display a modified command prompt while inside of the chroot environment. This will help you to identify when you are issuing commands inside of the 32-bit chroot as opposed to the x86-64bit host.

Add the following line at the end of the file profile inside of the directory /part/to/chroot/directory/etc/

root # nano etc/profile

   profile - /etc/profile inside of /path/to/chroot/directory/

# understand sequences such as \h, don't put anything special in it.
        PS1="${USER:-$(whoami 2>/dev/null)}@$(uname -n 2>/dev/null) \$ "
fi

# ADD THE FOLLOWING LINE TO IDENTIFY YOUR 32-BIT CHROOT ENVIRONMENT
PS1="(32-bit chroot) ${PS1}"

for sh in /etc/profile.d/*.sh ; do
        [ -r "$sh" ] && . "$sh"
done
unset sh

OpenRC Configuration

You can create an sys-apps/openrc service named chroot32 to automatically copy files and mount directories prior to accessing the 32-bit chroot environment. This service will include additional mounts for meta-repo and the Portage DISTDIR.

   Note

The following file mounts Funtoo portage tree /var/git/meta-repo as read-only. The Portage DISTDIR (/var/cache/portage/distfiles) is mounted read-write.

Create and edit the file /etc/init.d/chroot32, setting chroot_dir to equal /path/to/chroot/directory.

root # nano /etc/init.d/chroot32

   chroot32 - /etc/init.d/chroot32 on x86-64bit host

#!/sbin/openrc-run

chroot_dir=/path/to/chroot/directory

depend() {
   need localmount bootmisc
}

start() {
    ebegin "Mounting 32-bit chroot directories"
    mount --rbind /dev "${chroot_dir}/dev" >/dev/null
    mount --rbind /sys "${chroot_dir}/sys" >/dev/null
    mount -t proc none "${chroot_dir}/proc" >/dev/null
    mount -o bind /tmp "${chroot_dir}/tmp" >/dev/null
    mount -o bind,ro /var/git/meta-repo "${chroot_dir}/var/git/meta-repo/" >/dev/null
    mount -o bind /var/cache/portage/distfiles "${chroot_dir}/var/cache/portage/distfiles/" >/dev/null
    mount -t tmpfs -o nosuid,nodev,noexec,mode=755 none "${chroot_dir}/run" > /dev/null
    eend $? "An error occured while attempting to mount 32bit chroot directories"
    ebegin "Copying 32bit chroot files"
    cp -pf /etc/resolv.conf /etc/passwd /etc/shadow /etc/group \
           /etc/gshadow /etc/hosts "${chroot_dir}/etc" >/dev/null
    cp -Ppf /etc/localtime "${chroot_dir}/etc" >/dev/null
    eend $? "An error occured while attempting to copy 32 bits chroot files."
}

stop() {
    ebegin "Unmounting 32-bit chroot directories"
    umount -fR "${chroot_dir}/dev" >/dev/null
    umount -fR "${chroot_dir}/sys" >/dev/null
    umount -f "${chroot_dir}/proc" >/dev/null
    umount -f "${chroot_dir}/tmp" >/dev/null
    umount -f "${chroot_dir}/var/git/meta-repo/" >/dev/null
    umount -f "${chroot_dir}/var/cache/portage/distfiles/" >/dev/null
    umount -f "${chroot_dir}/run"
    eend $? "An error occured while attempting to unmount 32bit chroot directories"
}

Set this file to be executable.

root # chmod +x /etc/init.d/chroot32

Start the chroot32 service to prepare the 32-bit environment.

root # rc-service chroot32 start
 | * Mounting 32-bit chroot directories...                        [ ok ]
 | * Copying 32bit chroot files...                                [ ok ]

   Tip

If you would like this service to run during host startup issue the following command

root # rc-update add chroot32 default
 * service chroot32 added to runlevel default

The 32-bit chroot environment is now ready for access.

Enter 32-bit Chroot

Enter the 32-bit chroot environment with the following commands

user $ su -
Password: *******
root # linux32 chroot /path/to/chroot/directory /bin/bash -l
>>> Regenerating /etc/ld.so.cache...
chroot32 #

   Important

The switch -l tells bash to source /etc/profile within the chroot environment and not from the host. Without this switch you must manually issue the command source /etc/profile each time you enter the 32-bit environment.

Confirm that you are now in a 32-bit environment

chroot32 # uname -m
i686
chroot32 # epro show

=== Enabled Profiles: ===

        arch: x86-32bit
       build: current
     subarch: generic_32
      flavor: core
     mix-ins: (not set)


=== Python kit: ===

      branch: 3.7-release

=== All inherited flavor from core flavor: ===

                         minimal (from core flavor)

Chroot First Steps

If necessary now is a good point to set up Localization. Similarly, changes to /etc/portage/make.conf within the 32-bit environment can be made.

Currently you are the root user inside of the 32-bit environment. To change to the host user account localuser you must first create a home directory for localuser inside the 32-bit environment. (/home/localuser on the host is not mounted inside of this chroot environment.)

chroot32 # cp -r /etc/skel /home/localuser
chroot32 # chown -R localuser:localuser /home/localuser

Switch to 'localuser'

chroot32 # su localuser -l
user $

Updating Funtoo Meta-Repo

   Warning

Please be aware of this.

The 32-bit chroot environment uses the Meta-Repo (/var/git/meta-repo) of the 64bit host. Issuing ego sync is not necessary within the 32-bit chroot environment.

You must update Meta-Repo on the x86-64bit host before entering the 32-bit environment.

Exiting the 32-bit Chroot

(32-bit chroot) localhost / # exit
root ##g##localuser@localhost##!g## ~ $

Emerging Packages

Enter the 32-bit chroot environment and install packages normally.

root ##g##user@localhost##!g## $ su -
root ##i##Password:
root ##r##localhost##!r## # linux32 chroot /path/to/chroot/directory /bin/bash -l
>>> Regenerating /etc/ld.so.cache...
(32-bit chroot) localhost / # emerge -av foobar

   Tip

Depending on your use case it may be beneficial to change flavor and add mix-ins within the 32-bit environment.

Wine (32-bit only)

   Important

Before entering the 32-bit environment run the following command

root ##g##localuser@localhost##!g## $ su -
root ##i##Password:
root ##r##localhost##!r## # xhost local:localhost

This will allow X11 applications inside of the 32-bit environment to display on the host X session.

Install Wine inside of the 32-bit environment (example, No results)

(32-bit chroot) localhost / # emerge -av wine-vanilla

Instead of running wine as the root user, run as localuser. Switch to 'localuser' and configure Wine with winecfg. An X window should display.

(32-bit chroot) localhost / # su localuser -l
(32-bit chroot) localuser@localhost ~ $ winecfg

Acknowledgement

The information published here is based on steps detailed on the Gentoo Linux Wiki: https://wiki.gentoo.org/wiki/Project:AMD64/32-bit_Chroot_Guide (CC BY-SA 3.0).