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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-ssh-proxy"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>systemd-ssh-proxy</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-ssh-proxy</refentrytitle>
<manvolnum>1</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-ssh-proxy</refname>
<refpurpose>SSH client plugin for connecting to <constant>AF_VSOCK</constant> and
<constant>AF_UNIX</constant> sockets</refpurpose>
</refnamediv>
<refsynopsisdiv>
<programlisting>
Host unix/* vsock/* vsock-mux/*
ProxyCommand /usr/lib/systemd/systemd-ssh-proxy %h %p
ProxyUseFdpass yes
</programlisting>
<cmdsynopsis>
<command>/usr/lib/systemd/systemd-ssh-proxy</command> <arg>ADDRESS</arg> <arg>PORT</arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-ssh-proxy</command> is a small "proxy" plugin for the <citerefentry
project="man-pages"><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool that allows connecting to <constant>AF_UNIX</constant> and <constant>AF_VSOCK</constant> sockets. It
implements the interface defined by <filename>ssh</filename>'s <varname>ProxyCommand</varname>
configuration option. It's supposed to be used with an <citerefentry
project="man-pages"><refentrytitle>ssh_config</refentrytitle><manvolnum>5</manvolnum></citerefentry>
configuration fragment like the following:</para>
<programlisting>
Host unix/* vsock/* 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
</programlisting>
<para>A configuration fragment along these lines is by default installed into
<filename>/etc/ssh/ssh_config.d/20-systemd-ssh-proxy.conf</filename>.</para>
<para>With this in place, SSH connections to host string <literal>unix/</literal> followed by an absolute
<constant>AF_UNIX</constant> file system path to a socket will be directed to the specified socket, which
must be of type <constant>SOCK_STREAM</constant>. Similar, SSH connections to <literal>vsock/</literal>
followed by an <constant>AF_VSOCK</constant> CID will result in an SSH connection made to that
CID. <literal>vsock-mux/</literal> followed by an absolute <constant>AF_UNIX</constant> file system
path to a socket is similar but for cloud-hypervisor/firecracker which don't allow
direct <constant>AF_VSOCK</constant> communication between the host and guests, and provide their own
multiplexer over <constant>AF_UNIX</constant> sockets. See
<ulink url="https://github.com/cloud-hypervisor/cloud-hypervisor/blob/main/docs/vsock.md">cloud-hypervisor VSOCK support</ulink>
and <ulink url="https://github.com/firecracker-microvm/firecracker/blob/main/docs/vsock.md">Using the Firecracker Virtio-vsock Device</ulink>.</para>
<para>Moreover connecting to <literal>.host</literal> will connect to the local host via SSH, without
involving networking.</para>
<para>This tool is supposed to be used together with
<citerefentry><refentrytitle>systemd-ssh-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
which when run inside a VM or container will bind SSH to suitable
addresses. <command>systemd-ssh-generator</command> is supposed to run in the container of VM guest, and
<command>systemd-ssh-proxy</command> is run on the host, in order to connect to the container or VM
guest.</para>
</refsect1>
<refsect1>
<title>Exit status</title>
<para>On success, 0 is returned, a non-zero failure code
otherwise.</para>
</refsect1>
<refsect1>
<title>Examples</title>
<example>
<title>Talk to a local VM with CID 4711</title>
<programlisting>ssh vsock/4711</programlisting>
</example>
<example>
<title>Talk to a VM guest hosted with cloud-hypervisor/firecracker</title>
<programlisting>ssh vsock-mux/run/vm-1234.sock</programlisting>
</example>
<example>
<title>Talk to the local host via ssh</title>
<programlisting>ssh .host</programlisting>
<para>or equivalent:</para>
<programlisting>ssh unix/run/ssh-unix-local/socket</programlisting>
</example>
</refsect1>
<refsect1>
<title>See Also</title>
<para><simplelist type="inline">
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-ssh-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry project="man-pages"><refentrytitle>vsock</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
<member><citerefentry project="man-pages"><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
<member><citerefentry project="man-pages"><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry project="man-pages"><refentrytitle>sshd</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
</simplelist></para>
</refsect1>
</refentry>
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