Features/Migration/Troubleshooting

You're probably looking at this page because migration has just failed; sorry about that, but hopefully this page will give you some idea of how to figure out why and importantly what to include in any bug report.

Basics

QEMU's migration is like lifting the state out of one machine and dumping it into another - the (emulated) hardware of the two machines have to match pretty much exactly for this to succeed.

Note that QEMU supports migrating forward between QEMU versions but in general not backwards, although some distros support this on their packages QEMU versions.

Machine types

QEMU's machine types (the parameter to -M or --machine) is a definition of the basic shape of the emulated machine; the closest analogy is to the model of motherboard in a system. Migration requires you to have the same machine type on the source and destination machines. Architectures tend to have a variety of machine types (e.g. on x86 there is the 'pc' and the 'q35' family) that correspond to different generations of system. In addition some architectures version the machine types - e.g. pc-i440fx-2.5, pc-i440fx-2.6. Newer QEMUs normally keep (most of) the older machine types around so that you can migrate. So for example, a 2.6 release of QEMU should be able to migrate from a 2.5 release using the pc-i440fx-2.5 or pc-i440fx-2.4 machine types; Note it's not heavily tested!