QEMU Internals (2021)

FWIW, if you're comfortable with command-line, here's a way to use QEMU with `virt-builder`[a] and libvirt (the virtualization API):

(1) Download a Fedora image (or any one of the images that `virt-builder` supports: `virt-builder --list | less`)

    $> virt-builder fedora-36 --format qcow2 \
       -o vm1.qcow2 --root-password secret

(2) Import the image to libvirt:

    $> sudo virt-install --name vm1 --ram 4096 \
       --disk path=/var/lib/libvirt/images/vm1.qcow2,format=qcow2 \
       --nographics --os-variant fedora-36 --import

Then you can do various operations via `virsh` (the shell tool). Start a VM, and see the boot process on the serial console:

    $ sudo virsh start --console

Create a snapshot:

    $ sudo virsh snapshot-create-as vm1 snap1 "Clean Fedora 1"

With this kind of snapshot (called "internal snapshots"), the original and its delta, i.e. the snapshot, are stored in a single disk image file; this is convenient for moving it across machines. This only works with QCOW2 images. To revert to the snapshot:

    $ sudo virsh snapshot-revert vm1 snap1

And so on[b].

[a] https://libguestfs.org/virt-builder.1.html

[b] https://developer.fedoraproject.org/tools/virt-builder/about...

Now I tried Debian as well. It boots fine, but the username & password mentioned are incorrect. There's some way to go until this thing is usable I would say.

Does it work on Macs?

I like Virtual Machine Manager too. It's been a trusty workhorse for years. It had tried Vagrant and Docker and both didn't work out too well. With Docker being a container engine for instance, systemd doesn't work, so installing packages which start services and manage systemd units fails. There are some hacks and workaround but VMM just works as expected.