3proxy/doc/html/man8/3proxy.8.html
Vladimir Dubrovin 3520e6e7cf Hand listening sockets over on a reload
A service's TCP listening socket is kept as a listener: when a reload
commits, before the old services are told to stop, each new service
takes over the listener of an older configuration's service on the same
address, port, network namespace and device with the same -ol options.
It skips socket() and bind(), calling only listen() again for its own
backlog, and logs "Accepting connections, taken over". The old service
stops accepting at its next poll and lets go of the socket; whoever
lets go last closes it, unlinking a Unix socket's path.

So a service staying where it was no longer leaves a gap: before, the
old one closed its socket and the new one opened another, and a
connection queued on the old socket was reset. UDP services, whose
clients read from the service's socket, and two services of the same
configuration on one address keep their own sockets as before.

A test case makes requests nonstop through three reloads and wants none
refused or reset; against the build before this, connections were
reset. The reload case no longer waits out the switch. SIGUSR1 in
3proxy(8) describes how a reload behaves now.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-14 22:14:04 +03:00

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<h1 align="center">3proxy</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#SIGNALS">SIGNALS</a><br>
<a href="#FILES">FILES</a><br>
<a href="#BUGS">BUGS</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#AUTHORS">AUTHORS</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em"><b>3proxy</b> -
3[APA3A] tiny proxy server, or trivial proxy server, or free
proxy server</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em"><b>3proxy</b>
[<i>config_file</i>] <b><br>
3proxy</b> [<i>--install</i>] <b><br>
3proxy</b> [<i>--remove</i>]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em"><b>3proxy</b> is
a universal proxy server. It can be used to provide internal
users with fully controllable access to external resources
or to provide external users with access to internal
resources. 3proxy is not developed to replace
<b>squid</b>(8), but it can extend the functionality of an
existing caching proxy. It can be used to route requests
between different types of clients and proxy servers. Think
about it as application level gateway with configuration
like hardware router has for network layer. It can establish
multiple gateways with HTTP and HTTPS proxy with FTP over
HTTP support, SOCKS v4, v4.5 and v5, POP3 proxy, UDP and TCP
portmappers. Each gateway is started from the configuration
file like an independent service <b>proxy</b>(8)
<b>socks</b>(8) <b>pop3p</b>(8) <b>imapp</b>(8)
<b>tcppm</b>(8) <b>udppm</b>(8) <b>ftppr</b>(8) <b>dnspr</b>
but <b>3proxy</b> is not a kind of wrapper or superserver
for these daemons. It just has the same code compiled in,
but provides much more functionality. SOCKSv5 implementation
allows you to use 3proxy with any UDP or TCP based client
applications designed without proxy support (with
<i>SocksCAP</i>, <i>FreeCAP</i> or another client-side
redirector under Windows or with a socksification library
under Unix). So you can play your favourite games, listen to
music, exchange files and messages and even accept incoming
connections behind a proxy server.</p>
<p style="margin-left:9%; margin-top: 1em"><i>dnspr</i>
does not exist as an independent service. It&rsquo;s a DNS
caching proxy (it requires <i>nscache</i> and <i>nserver</i>
to be set in the configuration. Only A-records are cached.
Please note that this caching is mostly a &rsquo;hack&rsquo;
and has nothing to do with a real DNS server, but it works
perfectly for SOHO networks.</p>
<p style="margin-left:9%; margin-top: 1em">3proxy supports
access control lists (ACL) like network router. Source and
destination networks and destination port can be specified.
In addition, usernames and gateway action (for example GET
or POST) can be used in ACLs. In order to filter request on
username basis user must be authenticated somehow. There are
few authentication types including password authentication
and authentication by NetBIOS name for Windows clients
(it&acute;s very like ident authentication). Depending on
ACL action request can be allowed, denied or redirected to
another host or to another proxy server or even to a chain
of proxy servers.</p>
<p style="margin-left:9%; margin-top: 1em">It supports
different types of logging: to logfiles, <b>syslog</b>(3)
(only under Unix) or to an ODBC database. Logging format is
tunable to provide compatibility with existing log file
parsers. It makes it possible to use 3proxy with IIS, ISA,
Apache or Squid log parsers.</p>
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em"><b>config_file</b></p>
<p style="margin-left:18%;">Name of config file. See
<b>3proxy.cfg</b>(3) for configuration file format. Under
Windows, if config_file is not specified, <b>3proxy</b>
looks for a file named <i>3proxy.cfg</i> in the default
location (in the same directory as the executable file and
in the current directory). Under Unix, if no config file is
specified, 3proxy reads configuration from stdin. It makes
it possible to use the 3proxy.cfg file as an executable
script just by setting +x mode and adding <br>
#!/usr/local/3proxy/3proxy <br>
as a first line in 3proxy.cfg</p>
<p style="margin-left:9%;"><b>--install</b></p>
<p style="margin-left:18%;">(Windows NT family only)
install <b>3proxy</b> as a system service</p>
<p style="margin-left:9%;"><b>--remove</b></p>
<p style="margin-left:18%;">(Windows NT family only) remove
<b>3proxy</b> from system services</p>
<h2>SIGNALS
<a name="SIGNALS"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em">Under Unix there
are a few signals <b>3proxy</b> catches. See <b>kill</b>(1).
<b><br>
SIGTERM</b></p>
<p style="margin-left:18%;">clean up connections and
exit</p>
<p style="margin-left:9%;"><b>SIGPAUSE</b></p>
<p style="margin-left:18%;">stop accepting new connections,
on second signal - start and re-read configuration</p>
<p style="margin-left:9%;"><b>SIGCONT</b></p>
<p style="margin-left:18%;">start to accept new
connections</p>
<p style="margin-left:9%;"><b>SIGUSR1</b></p>
<p style="margin-left:18%;">reload configuration. The file is read whole before anything changes: if
it has an error, the configuration in force stays as it is, its services
running. Otherwise the new services start and the old ones stop accepting
within a second; connections already open finish under the old
configuration. A new service listening on the same address and port, in
the same network namespace and on the same device, with the same <b>-ol</b>
options, takes over the old service's TCP listening socket, so no
connection is refused or lost meanwhile; any other listening socket is
closed by the old service and opened by the new one. Settings left out of
the new file go back to their defaults.</p>
<p style="margin-left:9%; margin-top: 1em">Under Windows,
if <b>3proxy</b> is installed as a service you can use
standard service management to start, stop, pause and
continue the 3proxy service, for example: <b><br>
net start 3proxy <br>
net stop 3proxy <br>
net pause 3proxy <br>
net continue 3proxy</b></p>
<p style="margin-left:9%; margin-top: 1em">Web admin
service can also be used to reload configuration. Use wget
to automate this task.</p>
<h2>FILES
<a name="FILES"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em"><i>/usr/local/3proxy/3proxy.cfg
(3proxy.cfg)</i></p>
<p style="margin-left:18%;"><b>3proxy</b> configuration
file</p>
<h2>BUGS
<a name="BUGS"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em">Report all bugs
to <b>3proxy@3proxy.org</b></p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em">3proxy.cfg(5),
proxy(8), ftppr(8), socks(8), pop3p(8), imapp(8), tcppm(8),
udppm(8), kill(1), syslogd(8), <br>
https://3proxy.org/</p>
<h2>AUTHORS
<a name="AUTHORS"></a>
</h2>
<p style="margin-left:9%; margin-top: 1em">3proxy is
designed by Vladimir Dubrovin &lt;vlad@3proxy.org&gt;</p>
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