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Multiple Architectures

This guide shows how to install packages for more than one CPU architecture into the same rootfs. Some applications need that: Wine and Steam pull 32-bit libraries alongside 64-bit ones, and cross-compilation toolchains may need a second architecture to produce binaries for the target platform. Pass a comma-separated list to --arch and FlatRoot runs the install pipeline once per architecture, dropping each set of libraries into its own architecture-specific path so they do not conflict.

Install for multiple architectures

Pass a comma-separated list to --arch:

flatroot --from debian:bookworm --arch x86_64,i686 install --output ./root wine
Comma-separated, no spaces

The --arch list is split on commas; any whitespace becomes part of the architecture name. --arch x86_64,i686 works; --arch "x86_64, i686" produces an entry i686 (with leading space) that's rejected as an unknown architecture.

FlatRoot runs a separate resolve-download-extract pass for each architecture, all into the same rootfs. Libraries are placed in architecture-specific paths so they don't conflict:

./root/usr/lib/x86_64-linux-gnu/   # x86_64 libraries
./root/usr/lib/i386-linux-gnu/      # i686 libraries
Missing packages abort the install

If a user-requested package doesn't exist for one of the architectures in --arch, flatroot aborts with Package 'X' not found in the index. Architectures are processed sequentially, so later passes are never attempted after a failure, and files extracted by earlier passes remain on disk (no rollback). Before running a multiarch install, confirm the package exists for every target: flatroot --arch <each-arch> search '<pattern>'.

Other use cases

# Cross-compilation targeting aarch64
flatroot --from debian:bookworm --arch x86_64 install --output ./cross gcc-aarch64-linux-gnu libc6-dev

# Pure 32-bit environment
flatroot --from debian:bookworm --arch i686 install --output ./root32 python3

Architecture library paths

Architecture Debian library path
x86_64 /usr/lib/x86_64-linux-gnu/
i686 /usr/lib/i386-linux-gnu/
aarch64 /usr/lib/aarch64-linux-gnu/
armv7l /usr/lib/arm-linux-gnueabihf/
riscv64 /usr/lib/riscv64-linux-gnu/
Picking compatible distributions

Mixing architectures within one rootfs means picking a distribution release whose C library supports all of them. The glibc version table lists which flatroot remotes ship which glibc version and which ABIs each one serves.

Running a cross-arch rootfs

A cross-arch rootfs holds foreign-ELF binaries; the host kernel cannot execute them directly. To run them: (a) register qemu-user handlers with binfmt_misc so the host dispatches foreign binaries through qemu transparently — bwrap and chroot then just work — or (b) invoke binaries explicitly through the user-mode emulator, e.g. qemu-aarch64 ./rootfs/bin/sh with QEMU_LD_PREFIX=./rootfs. See bubblewrap and chroot for the wrapper side.

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