I don’t use VMs very often, so there’s no chance I can remember all the dozens
of command line flags for qemu.
I end up using virt-manager most of the time. It’s a GUI for managing
QEMU (and other VM backends) and has dozens of checkboxes and buttons, which
come in handy for really complex virtual hardware configurations where I’d need
to know a dozen obscure command line flags to replicate the same results.
virt-manager is also very handy for VMs with a graphical interface (e.g.: to
test something on Fedora or Ubuntu), but not so much when the only need is a
simple console.
After taking less than half an hour of reading, it turns out qemu is far
easier than I suspected. Should have done this years ago.
Basic VM ¶
The most basic VM simply starts a console with the alpine ISO:
qemu-system-x86_64 -nographic -drive file=alpine-virt-3.15.4-x86_64.iso,format=raw
By default qemu shows output in a separate window. It’s rather annoying because
it hijacks mouse, and doesn’t have the terminal’s regular copy-paste support.
-nographic prevents qemu from showing a separate window for graphic output
and uses the current terminal console instead.
CPU and Memory ¶
By default, the VM has a single CPU core and 128MB of RAM. This can be changed very easily:
qemu-system-x86_64 -m 1G -smp cores=2 -drive file=alpine-virt-3.15.4-x86_64.iso,format=raw
Network ¶
The internet is a kinda useful thing, and it’s nice to be able to use it inside
the VM. There’s the -net and -netdev flags, but those are really
complicated – mostly useful for more advanced configurations. For the most
basic setup (userspace NAT), -nic is the “new” flag which makes things dead
simple1:
qemu-system-x86_64 -nic user -nographic -drive file=alpine-virt-3.15.4-x86_64.iso,format=raw
After booting, network itself needs to be configured in the guest. For alpine, use:
ip link set eth0 up
udhcpc eth0
Putting it all together ¶
The following example defines CPU, memory and network:
qemu-system-x86_64 -nic user -nographic -m 1G -smp cores=2 -drive file=alpine-virt-3.15.4-x86_64.iso,format=raw
Architecture ¶
QEMU supports A LOT of architectures. For ARM64, use qemu-system-aarch64.
Make sure the ISO image’s architecture matches the VM’s architecture.