QEMU command-line: behavior of ‘-serial stdio’ vs. ‘-serial mon:stdio’

[Thanks: To Paolo Bonzini for writing the original patch; and to Alexander Graf for mentioning this on IRC some months ago, I had to go and look up the logs.]

I forget to remember: to avoid QEMU being terminated on SIGINT (Ctrl+c), instead of just stdio, supply the special parameter mon:stdio to -serial option (which redirects the virtual serial port to a host character device). The subtle difference between them:

• -serial stdio: Redirects the virtual serial port onto stdio; upon Ctrl+c, QEMU immediately terminates.
• -serial mon:stdio: In this mode, the virtual serial port and QEMU monitor are multiplexed onto stdio. And Ctrl+c is handled, i.e. QEMU won’t be terminated, and the signal will be passed to the guest.

In summary, a working example command-line:

$ qemu-system-x86_64               \
   -display none                   \
   -nodefconfig                    \
   -nodefaults                     \
   -m 2048                         \
   -device virtio-scsi-pci,id=scsi \
   -device virtio-serial-pci       \
   -serial mon:stdio  \
   -drive file=./fedora23.qcow2,format=qcow2,if=virtio

To toggle between QEMU monitor prompt and the serial console, use Ctrl+a, followed by typing ‘c’. To terminate QEMU, while at monitor prompt, (qemu), type ‘quit’.

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