SYSTEMD-SSH-PROXY(1)

NAME
systemd-ssh-proxy - SSH client plugin for connecting to AF_VSOCK and AF_UNIX sockets

SYNOPSIS

Host unix/* unix%* vsock/* vsock%* vsock-mux/* vsock-mux%*
    ProxyCommand /usr/lib/systemd/systemd-ssh-proxy %h %p
    ProxyUseFdpass yes

/usr/lib/systemd/systemd-ssh-proxy [ADDRESS] [PORT]

DESCRIPTION

systemd-ssh-proxy is a small "proxy" plugin for the ssh(1) tool that allows connecting to AF_UNIX and AF_VSOCK sockets. It implements the interface defined by ssh's ProxyCommand configuration option. It's supposed to be used with an ssh_config(5) configuration fragment like the following:

    Host unix/* unix%* vsock/* vsock%* vsock-mux/* vsock-mux%*
        ProxyCommand /usr/lib/systemd/systemd-ssh-proxy %h %p
        ProxyUseFdpass yes
        CheckHostIP no
    Host .host
        ProxyCommand /usr/lib/systemd/systemd-ssh-proxy unix/run/ssh-unix-local/socket %p
        ProxyUseFdpass yes
        CheckHostIP no

A configuration fragment along these lines is by default installed into /etc/ssh/ssh_config.d/20-systemd-ssh-proxy.conf.

With this in place, SSH connections to host string "unix/" followed by an absolute AF_UNIX file system path to a socket will be directed to the specified socket, which must be of type SOCK_STREAM. Similar, SSH connections to "vsock/" followed by an AF_VSOCK CID will result in an SSH connection made to that CID. "vsock-mux/" followed by an absolute AF_UNIX file system path to a socket is similar but for cloud-hypervisor/firecracker which do not allow direct AF_VSOCK communication between the host and guests, and provide their own multiplexer over AF_UNIX sockets. See cloud-hypervisor VSOCK support[1] and Using the Firecracker Virtio-vsock Device[2]. Note that "%" can be used as a separator instead of "/" to be compatible with tools like "scp" and "rsync".

Moreover, connecting to ".host" will connect to the local host via SSH, without involving networking.

This tool is supposed to be used together with systemd-ssh-generator(8) which when run inside a VM or container will bind SSH to suitable addresses. systemd-ssh-generator is supposed to run in the container or VM guest, and systemd-ssh-proxy is run on the host, in order to connect to the container or VM guest.

EXIT STATUS

On success, 0 is returned, a non-zero failure code otherwise.

EXAMPLES

Example 1. Talk to a local VM with CID 4711

    ssh vsock/4711

Example 2. Talk to a VM guest hosted with cloud-hypervisor/firecracker

    ssh vsock-mux/run/vm-1234.sock

Example 3. Talk to the local host via ssh

    ssh .host

or equivalent:

    ssh unix/run/ssh-unix-local/socket

Example 4. Copy local 'foo' file to a local VM with CID 1348

    scp foo vsock%1348:

SEE ALSO

systemd(1), systemd-ssh-generator(8), vsock(7), unix(7), ssh(1), sshd(8)

NOTES

1.  cloud-hypervisor VSOCK support
    https://github.com/cloud-hypervisor/cloud-hypervisor/blob/main/docs/vsock.md

2.  Using the Firecracker Virtio-vsock Device
    https://github.com/firecracker-microvm/firecracker/blob/main/docs/vsock.md