=================
Create an arm* VM
=================

Create a stretch/buster-elts armhf VM, to debug a failing package
build or testsuite. This works from an amd64 host, but isn't very
useful, see limitations below and :doc:`arm-debug` for a more
practical native solution.

.. code:: bash

  sudo apt install arch-test uidmap binfmt-support \
    qemu-system-arm qemu-user-static

  DIST=stretch # or buster, bullseye, etc.
  ARCH=armhf   # or arm64 (>= buster)
  debvm-create -r $DIST -o $DIST-$ARCH.ext4 \
    --size=3G -k ~/.ssh/id_xxx.pub \
    -- \
      --architecture=$ARCH \
      --keyring=/publicly/readable/freexian-archive-key.gpg \
      --include=freexian-archive-keyring \
      --include=linux-image-5.10-XXX \
      http://archive.debian.org/debian/ \
      "deb http://deb.freexian.com/extended-lts $DIST-lts main"
  # Note: the initramfs step may take several minutes

Using an ELTS 5.10 kernel backport may be required to boot, typically
for stretch/armhf or from an amd64 host. Replace XXX by the kernel for
your target architecture (``armmp`` for armhf, ``arm64`` for
arm64). 6.1 backports are also available.

See `<../technical-workflows.html#debvm>`_ for further useful
configuration.

Further customization possible, see ``man debvm-create``.

Now run the VM:

.. code:: bash

  debvm-run -i $DIST-$ARCH.ext4 --sshport 2222 -- -m 2G
  ssh -p 2222 -o StrictHostKeyChecking=no root@localhost

Limitations:

* The VM is not hardware-accelerated and quite slow on amd64 (CPU and
  I/O, 10-20x slower). This increases timeout-related issues. Using
  ``eatmydata`` helps a little, same for ``mount -t tmpfs none
  /mnt/workdir -o size=2G``, but the main bottleneck appears to be the
  CPU more than the disk.

* The VM does not behave exactly like the real buildd hardware,
  different errors may occur.

---------------
Troubleshooting
---------------

* *passwd: Cannot determine your user name.* (bookworm/0.2.10)

Apply https://salsa.debian.org/helmutg/debvm/-/commit/e4ecc7f745c54a765eff8eff59fc2e9a03371f2e

* init fails to mount disk, ``/dev/vda`` not present; or boot just
  stalls

Upgrade to a kernel backport: ``--include=linux-image-5.10-armmp``
(armhf) or ``--include=linux-image-5.10-arm64``.

---------------
Other resources
---------------

Pre-built images, with external kernel and initrd:

* https://people.debian.org/~aurel32/qemu/ (squeeze, wheezy)
* https://people.debian.org/~gio/dqib/ (sid)

Manual install from ISO:

* https://quantum5.ca/2020/12/26/how-to-make-an-arm-virtual-machine-armhf-aarch64/ (external kernel and initrd)
* https://quantum5.ca/2022/03/19/how-to-make-better-arm-virtual-machine-armhf-aarch64-uefi/ (UEFI, text-based Debian installer)