debvm-run1

Usage

Overview

debvm-run is essentially a thin wrapper around qemu for running a virtual machine image created by debvm-create or something compatible. The virtual machine image is expected to be a raw ext4 image with a non-empty file system label. The architecture of the machine is detected from the contained /bin/true. It must contain a symbolic link pointing to a kernel image at one of (|/boot)/vmlinu[xz] a symbolic link pointing to an initrd image at initrd.img in the same directory as the kernel image. Both are extracted and passed to qemu. A net interface configured for user mode is added automatically.

Options

--append=cmdline

While the kernel command line can be modified by passing -append to qemu directly, doing that always replaces the entire command line and thus removes important values passed by debvm-run. This variant instead appends given command line arguments to the automatic ones. Repeated use also causes appending rather than replacement.

-g, --graphical

By default, the option -nographic is passed to qemu and one interacts with the serial console of the machine. This configuration is skipped in the presence of this option. Note that debvm-create defaults to installing a cloud kernel if available, so you may have to pass "--include=linux-image-generic" during image construction to get graphics drivers.

-i image, --image=image

This option specifies the location of the virtual machine image file. By default rootfs.ext4 in the working directory is used.

--netopt=option

debvm-run sets up a user mode network by default. It therefore passes a -netdev option to qemu. Using this option, you can customize the value of that -netdev option. For instance, you can set up additional port forwards by passing e.g. "--netopt hostfwd=:127.0.0.1:8080-:80". It can be used multiple times.

--skip=task

Skip a particular task or feature. The option may be specified multiple times or list multiple tasks to be skipped by separating them with a comma. By default, no tasks are skipped. The following tasks may be skipped.

network

Do not configure a network card. Use this if you want to configure network on your own. This should also be passed in addition to passing "-nic none" when you want to disable networking.

rngdev

Do not pass a random number generator device.

root

Skip all of the following tasks matching "root/*". If either of these is present, the VM will not boot unless a suitable replacement is added in another way.

root/cmd

Since debvm-run uses qemu as bootloader it normally passes the label of the root block device via the kernel command line. This passing can be inhibited to supply a different location.

root/dev

A block device for the root filesystem is no longer passed. This can be used to customize the block device.

--transport=transport

When debvm adds devices to qemu, it has to select a transport and it most often guesses pci. When specifying a different machine such as -machine microvm, a different transport such as device may be needed.

-s sshport, --sshport=sshport

If given, qemu is configured to pass connections to 127.0.0.1:sshport to port 22 of the virtual machine. You can connect to your virtual machine without updating your known hosts like this:

    ssh -o NoHostAuthenticationForLocalhost=yes -p $sshport [email protected]

The option is a shorthand for "--netopt hostfwd=tcp:127.0.0.1:sshport-:22".

-- qemu options

All options beyond a double dash are passed to qemu. This can be used to configure additional hardware components. One possible use of this method is passing -snapshot to avoid modifying the virtual machine image.

Examples

Run a virtual machine stored in the image rootfs.ext4 (the default) with local port 8022 routed to port 22 of the virtual machine. The -snapshot argument is passed to QEMU and prevents any permanent changes to rootfs.ext4, resulting in an ephemeral run.

    debvm-run -s 8022 -i rootfs.ext4 -- -snapshot

Faq

The debvm-run console renders wrong.

Make sure $TERM is set to a value known inside the VM. You may need to install ncurses-term for more definitions. The serial console will miss events of resizing the terminal emulator. You may run "setterm --resize" in that case.

How can I kill debvm-run?

The wrapped qemu can be terminated by pressing Ctrl-a x. Refer to the qemu manual page for more escape sequences.

Limitations

Due to the way kernel and bootloader are being extracted before running qemu, one cannot upgrade a kernel and then just reboot. Attempting to do so, will still use the old kernel. Instead, qemu must be terminated and debvm-run should be launched again to pick up the new kernel. In order to avoid accidental reboots, one may pass -no-reboot to qemu.

For 32bit arm, highmem is actively disabled, because the default kernel flavour fails to boot. If you want to pass more ram, please also pass -machine virt and install a lpae kernel. Alternatively, use an arm64 kernel.