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 * [[https://k1024.org/posts/2023/2023-10-31-raspberry-pi-upgrade-crossgrade/|Raspberry PI OS: upgrading and cross-grading]]

Translation(s): Français

Cross-grading a Debian System

This page is meant to document the procedure for cross-grading a Debian install using Multiarch.

ToDo: the crossgrader package entered Debian in 2020, using it should be documented on this page. See https://salsa.debian.org/crossgrading-team/debian-crossgrading/-/blob/master/INSTRUCTIONS.md.


The first Debian release to feature Multiarch was Wheezy, so you may need to upgrade before attempting the procedure described here.

A full backup is also strongly recommended as this procedure is still very much work in progress. Reinstalling is still the safer option. You have been warned!

Run the upgrade commands from a text mode console, not from within a graphical terminal. Run the commands locally, or at least within a tmux or screen session.


These are the steps for converting an i386 install to amd64, but they should be applicable for any other architecture pairs if your machine can run both (e.g. armel and armhf). You can use arch-test to determine which Debian architectures your system can run. You can install qemu-user-static to add support for more Debian architectures.

Add the new architecture

# dpkg --print-architecture
# dpkg --add-architecture amd64
# dpkg --print-foreign-architectures
# apt update

Install a kernel that supports both architectures in userland

# apt install linux-image-amd64:amd64
# reboot

Make sure you are actually running the new kernel before proceeding with the next steps (uname -a).

Make sure all packages are in sync between architectures

You need to upgrade first, or otherwise check all the versions of packages to be crossgraded in this step, to make sure all amd64/i386 packages are in version-sync, otherwise the cross-grade will break.

# apt clean
# apt upgrade

Crossgrade dpkg, tar and apt

Get all the packages needed to replace dpkg, tar and apt, then install them for the new architecture. It is changing dpkg that actually 'counts' for changing the default architecture.

/!\ tar (and other dependencies of apt and dpkg) must be replaced at the same time as dpkg and apt. The dependencies seem to be different in different Debian releases:

  • For buster: add just tar:amd64

  • For bullseye: add tar:amd64 apt-utils:amd64 perl-base:amd64

  • For ~2020-10 sid: add tar:amd64 apt:amd64 apt-utils:amd64 perl-base:amd64 libsystemd0:amd64

  • For bookworm: ??

To install packages together, first download them with apt and then install all of them with dpkg.

Run apt clean to be sure /var/cache/apt/archives/ is empty and then in following steps you can glob-install everything in that directory.

# apt --download-only install dpkg:amd64 tar:amd64 apt:amd64
## on bullseye, you will need the following packages in addition
# apt --download-only install apt-utils:amd64 perl-base:amd64
## 2020-10 Debian sid: apt --download-only install dpkg:amd64 tar:amd64 apt:amd64 libsystemd0:amd64
## due to pre-dependencies you may have to run this command more than once to unpack and configure all packages
# dpkg --install /var/cache/apt/archives/*_amd64.deb
# dpkg --print-architecture
# dpkg --print-foreign-architectures
# apt update
# apt upgrade
# apt full-upgrade

Notes 2020-10 Debian sid: the download step also needs libsystemd0:amd64. If get errors about a missing libsystemd0 and can no longer run apt, you can still directly download libsystemd0 and put the .deb in /var/cache/apt/archives/. Then run dpkg --install /var/cache/apt/archives/*_amd64.deb again. After that apt upgrade still did not work but apt install -f worked without needing to type the 'Yes, do as I say'.

Crossgrade all other architecture-dependent packages

If you got this far you are now effectively running amd64, but with mostly i386 packages.

Before a mass replacement from old to new architectures, if you have packages without installation candidates (from old releases), you may want to first try removing those with

# apt purge '?obsolete'

You can try to replace them with the corresponding amd64 packages. It should be possible to remove the i386 package and install the amd64 version instead. Not all libraries will necessarily support Multiarch, so they may not have a direct replacement.

Preserving the "auto" mark

Also note that manually upgrading packages will clear the "automatically installed" flag (for those packages that were automatically installed on i386).

If it works for you, the best way to do the swap that preserves all of dpkg and apt state regarding manual vs automatic package selection is

# apt-mark showauto | sed -n -e's/:i386$//p' > auto-package-list
# apt install $(dpkg -l | awk '$1 ~ /^.i/ && $2 ~ /:i386$/ { sub(":i386", ""); print $2 }')
# xargs apt-mark auto < auto-package-list

You will have to type in 'Yes, do as I say' to get apt to do this, so make sure each package in the warning is actually going to get installed with the new architecture.

This method also has the advantage that if you have packages installed that are only available on i386, they will be kept installed rather than throwing an error about unavailable packages.

Notes 2020-10: I needed to edit the list to remove the pae kernel references and then use that edited list from a file for apt install. You will experience various errors regardless. I needed to for example manually dpkg -i bash and dash, symlink /bin/sh to the existing one a couple of times, and try again and again. Do not expect not needing to do a lot of apt install -f, dpkg --configure -a, and manual dpkg -i from /var/cache/apt/archives/ and apt autoremove --purge (to remove replaced :i386 binaries). However using above and these notes I ended up with a functional system and there were big portions that just ran without interruptions.

Bulk crossgrade of all remaining i386 packages

Another more brutal way to do the swap is

# dpkg --get-selections | grep '\binstall$' | grep :i386 | sed -e s/:i386/:amd64/ | dpkg --set-selections
# apt -f install

You will have to type in 'Yes, do as I say' to get apt to do this.

Once the swap is complete, you can remove all the redundant libraries and drop the old architecture with

# apt purge $(dpkg -l | grep '^.i.*:i386' | awk '{print $2}')
# dpkg --remove-architecture i386
# apt update

Caveats and Known Problems

Caution with systemd

systemd may not like being cross-graded, possibly it is safer to cross-grade it from a liveCD. Make sure to cross-grade udev at the same time, otherwise various units will fail.

APT dependency resolver wants to revert apt itself

If the system had packages that depend on apt like apt-utils, it's possible run into a situation where apt -f install wants to revert apt itself to i386. Aborting and doing another operation apt autoremove will illustrate the reason better:

The following packages have unmet dependencies:
 apt-utils:i386 : Depends: apt:i386 (= 1.4.8) but it is not installed

In such a case, the solution is to temporarily remove apt-utils:i386 from the system, and install apt-utils afterwards. Note: this new apt-utils will be amd64, but once you switch apt to amd64, using the :amd64 suffix will not work.

Apt dependency resolver generates broken solutions

It might happen that apt's resolver emits an unworkable solution:

E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
E: Unable to correct dependencies

In this case you can inspect what packages are marked as Broken and decide what to do:

# apt -o Debug::pkgProblemResolver=1 -f install


The KDE desktop environment creates the file ~/.config/Trolltech.conf which contains locations of shared libararies and, more problematic, their architecture. This causes panel widgets to crash. The file can apparently be safely removed or renamed to fix these problems.

iamerican (and possibly others/similar)

Similar to KDE, some package(s) (e.g. iamerican on at least Debian 7.5) may have saved caches/hashes that need updating. E.g. encountered:

$ echo foo | spell
/usr/bin/ispell: Illegal format hash table

corrected with:

# (cd / && umask 022 && dpkg-reconfigure iamerican)

which then caused updating of: /var/lib/ispell/american.hash

Sample cross-grade script

Here is a script to essentially do the above for you. It could do with some work to put in a lot more error checking, but it works OK on a build-essential basic chroot - you may have problems on a more fully-configured real system. Use at your own risk!

# scary script to crossgrade your debian machine between arches.
# usage crossgrade <final-architecture>
set -e

if [ -z "$1" ]; then
  echo "Usage: crossgrade <architecture>  (debian architecture to convert to)"
  exit 1

#validate arch
if ! TO=$(dpkg-architecture -qDEB_HOST_ARCH -a$1); then
    echo "$1 is not a recognised architecture name"
    exit 1
FROM=$(dpkg --print-architecture)
echo "Crossgrading from $FROM to $TO"

#check for a compatible kernel
# should check $FROM and $TO harder
# allow for switching kernel over too to minimal one if requested?
case $TO in

dpkg --add-architecture $TO
# check that dpkg --print-foreign-architectures is $TO
apt update
apt upgrade

# Install a kernel capable to run the new architecture with the old
# architecture in userspace

KERNEL=$(uname -m)
echo "Current kernel arch is $KERNEL"
if [ "$KERNEL" != "$TO_KERN" ]; then
    if apt install linux-image-$TO:$TO; then
        echo "There should be a reboot here"
        exit 1
        echo "kernel updating to linux-image-$TO:$TO failed"

echo Crossgrading dpkg and apt
apt clean
apt --download-only install dpkg:$TO apt:$TO tar:$TO

#check ever package to be installed is available in same version for amd64 if installed (multiarch sync is needed)
#for pkg in /var/cache/apt/archives/*_$TO.deb
#    file=$(basename $pkg)
#    pkgname= ${file%%_.*}
#    version= ${file##*._}
#    if dpkg -l $($pkgname)
#in practice this needs to run twice (do it more? is there a better way?)
if ! dpkg --install /var/cache/apt/archives/*_$TO.deb; then
    dpkg --install /var/cache/apt/archives/*_$TO.deb

test $(dpkg --print-architecture) = $TO
test $(dpkg --print-foreign-architectures | grep $FROM) = $FROM

echo "Yay! dpkg and apt crossgrade completed successfully"

echo "Updating core packages"
apt upgrade
apt full-upgrade

echo "Removing obsolete packages"
apt install aptitude:$TO
aptitude purge '?obsolete'

echo "Mass reinstalling $TO packages -- double check installed packages match warned-about packages"
apt install $(dpkg -l | grep '^.i.*:'"$FROM" | grep ":$FROM" | sed -e "s/:$FROM/:$TO/" | awk '{print $2}')

echo "Removing redundant libraries"
apt purge $(dpkg -l | grep '^.i.*:'"$FROM" | awk '{print $2}')

echo "Removing $FROM"
dpkg --remove-architecture "$FROM"
apt update