socket_vmnet: vmnet.framework support for rootless and VDE-less QEMU

socket_vmnet provides vmnet.framework support for QEMU.

socket_vmnet does not require QEMU to run as the root user.

(But socket_vmnet itself has to run as the root, in most cases.)

socket_vmnet was forked from vde_vmnet v0.6.0. Unlike vde_vmnet, socket_vmnet does not depend on VDE.

• Install
  • From Homebrew
  • From MacPorts
  • From source
• Usage
  • QEMU
  • Lima
• Advanced usage
  • Multi VM
  • Bridged mode
• FAQs
  • Why does socket_vmnet require root?
  • Is it possible to run socket_vmnet with SETUID?
  • How is socket_vmnet related to vde_vmnet?
  • How is socket_vmnet related to QEMU-builtin vmnet support?
  • How to use static IP addresses?
  • How to reserve DHCP addresses?
  • IP address is not assigned
• Links
• Troubleshooting

Install

Requires macOS 10.15 or later.

From Homebrew

brew install socket_vmnet

The binaries will be installed onto the following paths:

• ${HOMEBREW_PREFIX}/opt/socket_vmnet/bin/socket_vmnet
• ${HOMEBREW_PREFIX}/opt/socket_vmnet/bin/socket_vmnet_client

The ${HOMEBREW_PREFIX} path defaults to /opt/homebrew on ARM, /usr/local on Intel.

The ${HOMEBREW_PREFIX}/opt/socket_vmnet directory is usually symlinked to ../Cellar/socket_vmnet/${VERSION}.

Run the following command to start the daemon:

mkdir -p ${HOMEBREW_PREFIX}/var/run
sudo ${HOMEBREW_PREFIX}/opt/socket_vmnet/bin/socket_vmnet --vmnet-gateway=192.168.105.1 ${HOMEBREW_PREFIX}/var/run/socket_vmnet

Warning

Typically, the socket_vmnet binary in the ${HOMEBREW_PREFIX} can be replaced by any user in the admin group.

Launchd (optional, not needed for Lima)

To install the launchd service:

brew tap homebrew/services
# sudo is necessary for the next line
sudo ${HOMEBREW_PREFIX}/bin/brew services start socket_vmnet

The launchd unit file will be installed as /Library/LaunchDaemons/homebrew.mxcl.socket_vmnet.plist.

Default configuration:

Config	Value
Socket	${HOMEBREW_PREFIX}/var/run/socket_vmnet
Stdout	${HOMEBREW_PREFIX}/var/log/socket_vmnet/stdout
Stderr	${HOMEBREW_PREFIX}/var/log/socket_vmnet/stderr
Gateway	192.168.105.1

To uninstall the launchd service:

sudo ${HOMEBREW_PREFIX}/bin/brew services stop socket_vmnet

From MacPorts

sudo port install socket_vmnet

The binaries will be installed onto the following paths:

• /opt/local/bin/socket_vmnet
• /opt/local/bin/socket_vmnet_client

Run the following command to start the daemon manually:

sudo /opt/local/bin/socket_vmnet --vmnet-gateway=192.168.105.1  /var/run/socket_vmnet

Launchd (optional, not needed for Lima)

To install the launchd service:

sudo port load socket_vmnet

The launchd unit file will be installed as /Library/LaunchDaemons/org.macports.socket_vmnet.plist.

Default configuration:

Config	Value
Socket	/var/run/socket_vmnet
Stdout	/var/log/socket_vmnet.log
Gateway	192.168.105.1

To uninstall the launchd service:

sudo port unload socket_vmnet

From source

sudo make PREFIX=/opt/socket_vmnet install.bin

The PREFIX dir below does not necessarily need to be /opt/socket_vmnet, however, it is highly recommended to set the prefix to a directory that can be only written by the root.

Note that /usr/local/bin is sometimes chowned for a non-admin user, so /usr/local is not an appropriate prefix.

The binaries will be installed onto the following paths:

• /opt/socket_vmnet/bin/socket_vmnet
• /opt/socket_vmnet/bin/socket_vmnet_client

Run the following command to start the daemon:

sudo /opt/socket_vmnet/bin/socket_vmnet --vmnet-gateway=192.168.105.1 /var/run/socket_vmnet

Launchd (optional, not needed for Lima)

To install the launchd service:

sudo make PREFIX=/opt/socket_vmnet install.launchd

The launchd unit file will be installed as /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.plist.

Default configuration:

Config	Value
Socket	/var/run/socket_vmnet
Stdout	/var/log/socket_vmnet/stdout
Stderr	/var/log/socket_vmnet/stderr
Gateway	192.168.105.1

To uninstall the launchd service:

sudo make PREFIX=/opt/socket_vmnet uninstall.launchd

Usage

QEMU

Make sure that the socket_vmnet daemon is running, and execute QEMU via socket_vmnet_client as follows:

${HOMEBREW_PREFIX}/opt/socket_vmnet/bin/socket_vmnet_client \
  ${HOMEBREW_PREFIX}/var/run/socket_vmnet \
  qemu-system-x86_64 \
  -device virtio-net-pci,netdev=net0 -netdev socket,id=net0,fd=3 \
  -m 4096 -accel hvf -cdrom ubuntu-22.04-desktop-amd64.iso

The guest IP is assigned by the DHCP server provided by macOS.

The guest is accessible to the internet, and the guest IP is accessible from the host.

To confirm, run sudo apt-get update && sudo apt-get install -y apache2 in the guest, and access the guest IP via Safari on the host.

Lima

Lima (since v0.12.0) provides built-in support for socket_vmnet:

$ limactl sudoers | sudo tee /etc/sudoers.d/lima
$ limactl start --name=default template://vmnet

See also https://github.com/lima-vm/lima/blob/master/docs/network.md

Advanced usage

Multi VM

Multiple VMs can be connected to a single socket_vmnet instance.

Make sure to specify unique MAC addresses to VMs: -device virtio-net-pci,netdev=net0,mac=de:ad:be:ef:00:01 .

NOTE: don't confuse MAC addresses of VMs with the MAC address of socket_vmnet itself that is printed as vmnet_mac_address in the debug log. You do not need to configure (and you can't, currently) the MAC address of socket_vmnet itself.

Bridged mode

See ./launchd/io.github.lima-vm.socket_vmnet.bridged.en0.plist.

Install:

BRIDGED=en0
sed -e "s@/opt@${HOMEBREW_PREFIX}/opt@g; s@/var@${HOMEBREW_PREFIX}/var@g; s@en0@${BRIDGED}@g" ./launchd/io.github.lima-vm.socket_vmnet.bridged.en0.plist \
  | sudo tee /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}.plist
sudo launchctl bootstrap system /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}.plist
sudo launchctl enable system/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}
sudo launchctl kickstart -kp system/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}

Use ${HOMEBREW_PREFIX}/var/run/socket_vmnet.bridged.en0 as the socket.

Uninstall:

BRIDGED=en0
sudo launchctl bootout system /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}.plist
sudo rm /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}.plist

FAQs

Why does socket_vmnet require root?

Running socket_vmnet without root could be possible by signing the socket_vmnet binary with com.apple.vm.networking entitlement.

However, signing a binary with com.apple.vm.networking entitlement seems to require some contract with Apple. :disappointed:

This entitlement is restricted to developers of virtualization software. To request this entitlement, contact your Apple representative.

https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_vm_networking

Is it possible to run socket_vmnet with SETUID?

Yes, but discouraged, as it allows non-root users to write arbitrary files, by specifying certain CLI args and environment variables.

Instead, consider using launchd or sudo.

See ./etc_sudoers.d/socket_vmnet to allow running sudo socket_vmnet with reduced set of args and environment variables.

How is socket_vmnet related to vde_vmnet?

socket_vmnet was forked from vde_vmnet v0.6.0. Unlike vde_vmnet, socket_vmnet does not depend on VDE.

How is socket_vmnet related to QEMU-builtin vmnet support?

QEMU 7.1 added the built-in support for vmnet.

However, QEMU-builtin vmnet requires running the entire QEMU process as root.

On the other hand, socket_vmnet does not require the entire QEMU process to run as root, though socket_vmnet has to run as root.

How to use static IP addresses?

When --vmnet-gateway=IP is set to "192.168.105.1", the whole subnet (192.168.105.2-192.168.105.254) is used as the DHCP range.

To use static IP addresses, limit the DHCP range with --vmnet-dhcp-end=IP.

For example, --vmnet-gateway=192.168.105.1 --vmnet-dhcp-end=192.168.105.100 allows using 192.168.105.101-192.168.105.254 as non-DHCP static addresses.

How to reserve DHCP addresses?

• Decide a unique MAC address for the VM, e.g. de:ad:be:ef:00:01.

• Decide a reserved IP address, e.g., "192.168.105.100"

• Create /etc/bootptab like this. Make sure not to drop the "%%" header.

# bootptab
%%
# hostname      hwtype  hwaddr              ipaddr          bootfile
tmp-vm01        1       de:ad:be:ef:00:01   192.168.105.100

• Reload the DHCP daemon.

sudo /bin/launchctl kickstart -kp system/com.apple.bootpd

• Run QEMU with the MAC address: -device virtio-net-pci,netdev=net0,mac=de:ad:be:ef:00:01 .

NOTE: don't confuse MAC addresses of VMs with the MAC address of socket_vmnet itself that is printed as vmnet_mac_address in the debug log. You do not need to configure (and you can't, currently) the MAC address of socket_vmnet itself.

IP address is not assigned

Try the following commands:

/usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/libexec/bootpd
/usr/libexec/ApplicationFirewall/socketfilterfw --unblock /usr/libexec/bootpd

Links

• https://developer.apple.com/documentation/vmnet
• https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_vm_networking
• file:///Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/vmnet.framework/Versions/Current/Headers/vmnet.h

Troubleshooting

• Set environment variable DEBUG=1
• See ${HOMEBREW_PREFIX}/var/log/socket_vmnet/{stdout,stderr} (when using launchd). The path was previously ${HOMEBREW_PREFIX}/var/run/socket_vmnet.{stdout,stderr} until March 2023.