emu-cli: a small control toolkit for qemu

emu-cli installs the emu tool, which is a CLI program currently aimed at making x86 VM usage easier for Linux desktop users.

See a video of it in action: YouTube

It contains commands to:

• Manage VMs as a system-wide fleet
  • List all VMs in one place, along with their run status
  • Clone and Import VMs from other sources
• Create, Delete, Start, Stop, and Reboot VMs
  • ISOs can be attached
  • You can start VMs with or without graphical screens
  • emu does not have to be running to maintain your VM
• Import and Clone VM images
• Maintain snapshots and save states
• Supervise VMs with systemd
  • Uses the user profile (systemctl --user)
  • Knows about which systemd units its maintaining
    • Deletes them when the VM is deleted
• Manage settings for VMs
  • RAM, CPUs, Video & CPU type
  • Forward Ports to VM networks
• Define a SSH port that stays with the VM and emu ssh to it easily
• Poke and prod at your VMs with emu nc, which opens a TCP socket to the port on the VM
• Play with qemu QMP commands to control your VM externally

Requirements

Linux with systemd and qemu. It places things according to the XDG standards, so that means $HOME/.local will have the VMs, etc.

Most architectures should be supported; emu is used by the author on both x86 and Apple M1 (via Asahi Linux) architectures.

To build the software, you will need a working rust environment. I strongly recommend rustup.

Stability

emu is still undergoing some UI changes. I do use it somewhat regularly, but there may be additional work that needs to be done for a larger goal that changes small things as they stand now.

emu has bugs, particularly nasty ones at times related to your VMs. I would not use emu in a setting where data integrity mattered much.

Installation

cargo install emu-cli

Once installed, you can invoke the software with emu.

Usage

$ emu create myvm 50 # gigabytes of storage

# start the vm with the cdrom set to the ubuntu iso. Press ^C to terminate the vm.
$ emu run myvm --cdrom ubuntu.iso

# make a copy before doing something dumb
$ emu clone myvm myvm.template
$ emu list
myvm (unsupervised) (size: 6.10 GB)
myvm.template (unsupervised) (size: 6.10 GB)

# supervision in systemd
$ emu supervise myvm
$ emu supervised
myvm: not running
$ systemctl --user start myvm.emu # or enable it, if you'd like. it sticks to your login session.
$ emu list
myvm (supervised: running) (size: 6.10 GB)
myvm.template (unsupervised) (size: 6.10 GB)
$ systemctl --user stop myvm.emu # graceful shutdown
$ emu unsupervise myvm

# run detached and without a screen
$ emu run --detach --headless myvm
$ emu list
myvm (pid: 8675309) (size: 6.10 GB)
myvm.template (unsupervised) (size: 6.10 GB)

# ssh support
$ emu config port map myvm 2222 22
$ emu config set myvm ssh-port 2222
$ emu ssh myvm
myvm$ exit

# nc support
$ emu config port map myvm 8000 80
$ emu nc myvm 8000
GET / HTTP/1.1
Host: localhost
HTTP/1.1 403 Forbidden
Connection: close

# cleanup
$ emu shutdown myvm
$ emu remove myvm
$ emu list
myvm.template (unsupervised) (6.10 GB)

Configuration

Configuration is provided currently by injecting values into a file under ~/.local/share/emu/<VM>/config. It is in TOML format.

Configuration Values

[machine] section:

• memory: integer; memory in megabytes. Default is 16384.
• cpus: integer; count of CPU cores. Default is 8.
• vga: string; name of VGA driver to use with qemu -vga. Default is virtio.
• image_interface: string; name of interface to use for talking to images with -drive. Default virtio is recommended.
• cpu_type: string; type of CPU to support. Must be x86 and valid to pass to qemu -cpu. Default host is recommended.
• ssh_port: integer; port to contact for SSH access; used by emu ssh. Default is 2222.

[ports] is just a key/value map of host ports, opened on localhost, to guest ports, opened on 0.0.0.0. No other processing is performed.

Configuration Example

[machine]
cpus = 4
memory = 512

[ports]
2222 = 22

Management Tool

You can control these values with emu config <subcommand> sub-commands. emu config show, emu config set, and emu config port can be used to manage these sections.

The commands for emu config set are the same as the above [machine] section keys, only the underscores (_) are replaced with dashes (-); so that ssh_port is now ssh-port.

$ emu config show myvm
[machine]
cpus = 4
memory = 512

[ports]
2222 = 22

$ emu config port map myvm 2223 23
$ emu config port unmap myvm 2223

$ emu config set myvm ssh-port 2222
$ emu config set myvm cpus 8

$ emu config show myvm
[machine]
cpus = 8
memory = 512
ssh_port = 2222

[ports]
2222 = 22
2223 = 23

License

MIT

Author

Erik Hollensbe github@hollensbe.org