QEMU Guest Agent (qemu-ga) is a daemon intended to be run within virtual
machines. It allows the hypervisor host to perform various operations in
the guest, such as:
- get information from the guest,
- set the guest's system time,
- read/write a file,
- sync and freeze the filesystems,
- suspend the guest,
- reconfigure guest local processors,
- set user's password.

Note that qemu-ga (QEMU Guest Agent) is also part of the standard QEMU
installation. This package is intended for guests only, so that you don't have
to install the complete qemu package there. In general, do not install both
qemu-guest-agent and qemu packages at the same time on the same machine.

Use rc.qemu-ga to launch the daemon at boot and to stop it at shutdown.
You will need to perform host side setup too, to take the advantage of qemu-ga.