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<refentry id="systemd-socket-proxyd"
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-socket-proxyd</title>
    <productname>systemd</productname>
  </refentryinfo>
  <refmeta>
    <refentrytitle>systemd-socket-proxyd</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>
  <refnamediv>
    <refname>systemd-socket-proxyd</refname>
    <refpurpose>Bidirectionally proxy local sockets to another (possibly remote) socket.</refpurpose>
  </refnamediv>
  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-socket-proxyd</command>
      <arg choice="opt" rep="repeat"><replaceable>OPTIONS</replaceable></arg>
      <arg choice="plain"><replaceable>HOST</replaceable>:<replaceable>PORT</replaceable></arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>systemd-socket-proxyd</command>
      <arg choice="opt" rep="repeat"><replaceable>OPTIONS</replaceable></arg>
      <arg choice="plain"><replaceable>UNIX-DOMAIN-SOCKET-PATH</replaceable>
      </arg>
    </cmdsynopsis>
  </refsynopsisdiv>
  <refsect1>
    <title>Description</title>
    <para>
    <command>systemd-socket-proxyd</command> is a generic
    socket-activated network socket forwarder proxy daemon for IPv4,
    IPv6 and UNIX stream sockets. It may be used to bi-directionally
    forward traffic from a local listening socket to a local or remote
    destination socket.</para>

    <para>One use of this tool is to provide socket activation support
    for services that do not natively support socket activation. On
    behalf of the service to activate, the proxy inherits the socket
    from systemd, accepts each client connection, opens a connection
    to a configured server for each client, and then bidirectionally
    forwards data between the two.</para>
    <para>This utility's behavior is similar to
    <citerefentry project='die-net'><refentrytitle>socat</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
    The main differences for <command>systemd-socket-proxyd</command>
    are support for socket activation with
    <literal>Accept=false</literal> and an event-driven
    design that scales better with the number of
    connections.</para>
  </refsect1>
  <refsect1>
    <title>Options</title>
    <para>The following options are understood:</para>
    <variablelist>
      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
      <varlistentry>
        <term><option>--connections-max=</option></term>
        <term><option>-c</option></term>

        <listitem><para>Sets the maximum number of simultaneous connections, defaults to 256.
        If the limit of concurrent connections is reached further connections will be refused.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  <refsect1>
    <title>Exit status</title>
    <para>On success, 0 is returned, a non-zero failure
    code otherwise.</para>
  </refsect1>
  <refsect1>
    <title>Examples</title>
    <refsect2>
      <title>Simple Example</title>
      <para>Use two services with a dependency and no namespace
      isolation.</para>
      <example>
        <title>proxy-to-nginx.socket</title>
        <programlisting><![CDATA[[Socket]
ListenStream=80

[Install]
WantedBy=sockets.target]]></programlisting>
      </example>
      <example>
        <title>proxy-to-nginx.service</title>
        <programlisting><![CDATA[[Unit]
Requires=nginx.service
After=nginx.service
Requires=proxy-to-nginx.socket
After=proxy-to-nginx.socket

[Service]
ExecStart=/usr/lib/systemd/systemd-socket-proxyd /run/nginx/socket
PrivateTmp=yes
PrivateNetwork=yes]]></programlisting>
      </example>
      <example>
        <title>nginx.conf</title>
        <programlisting>
<![CDATA[[…]
server {
    listen       unix:/run/nginx/socket;
    […]]]>
</programlisting>
      </example>
      <example>
        <title>Enabling the proxy</title>
        <programlisting><![CDATA[# systemctl enable --now proxy-to-nginx.socket
$ curl http://localhost:80/]]></programlisting>
      </example>
    </refsect2>
    <refsect2>
      <title>Namespace Example</title>
      <para>Similar as above, but runs the socket proxy and the main
      service in the same private namespace, assuming that
      <filename>nginx.service</filename> has
      <varname>PrivateTmp=</varname> and
      <varname>PrivateNetwork=</varname> set, too.</para>
      <example>
        <title>proxy-to-nginx.socket</title>
        <programlisting><![CDATA[[Socket]
ListenStream=80

[Install]
WantedBy=sockets.target]]></programlisting>
      </example>
      <example>
        <title>proxy-to-nginx.service</title>
        <programlisting><![CDATA[[Unit]
Requires=nginx.service
After=nginx.service
Requires=proxy-to-nginx.socket
After=proxy-to-nginx.socket
JoinsNamespaceOf=nginx.service

[Service]
ExecStart=/usr/lib/systemd/systemd-socket-proxyd 127.0.0.1:8080
PrivateTmp=yes
PrivateNetwork=yes]]></programlisting>
      </example>
      <example>
        <title>nginx.conf</title>
        <programlisting><![CDATA[[…]
server {
    listen       8080;
    […]]]></programlisting>
      </example>
      <example>
        <title>Enabling the proxy</title>
        <programlisting><![CDATA[# systemctl enable --now proxy-to-nginx.socket
$ curl http://localhost:80/]]></programlisting>
      </example>
    </refsect2>
  </refsect1>
  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>socat</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>nginx</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>curl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>