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<chapter id="libpq">

<title><application>libpq</application> - C Library</title>

<para>

This option determines whether or with what priority a

<acronym>SSL</> TCP/IP connection will be negotiated with the

server. There are four modes: <literal>disable</> will attempt

only an unencrypted <acronym>SSL</> connection;

<literal>allow</> will negotiate, trying first a

non-<acronym>SSL</> connection, then if that fails, trying an

<acronym>SSL</> connection; <literal>prefer</> (the default)

will negotiate, trying first an <acronym>SSL</> connection,

then if that fails, trying a regular non-<acronym>SSL</>

connection; <literal>require</> will try only an

<acronym>SSL</> connection. <literal>sslmode</> is ignored

for Unix domain socket communication.

</para>

server. There are four modes:

<table id="libpq-connect-sslmode-options">

<title><literal>sslmode</literal> options</title>

<tgroup cols="2">

<thead>

<row>

<entry>Option</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><literal>disable</></entry>

<entry>only try a non-<acronym>SSL</> connection

</row>

<row>

<entry><literal>allow</></entry>

<entry>first try a non-<acronym>SSL</>

connection; if that fails, try an <acronym>SSL</>

connection</entry>

</row>

<row>

<entry><literal>prefer</> (default)</entry>

<entry>first try an <acronym>SSL</> connection; if

that fails, try a non-<acronym>SSL</>

connection</entry>

</row>

<row>

<entry><literal>require</></entry>

<entry>only try an <acronym>SSL</> connection</entry>

</row>

</tbody>

</tgroup>

</table>

<para>

<literal>sslmode</> is ignored for Unix domain socket

communication.

If <productname>PostgreSQL</> is compiled without SSL support,

using option <literal>require</> will cause an error, while

options <literal>allow</> and <literal>prefer</> will be

accepted but <application>libpq</> will notin fact attempt

accepted but <application>libpq</> will notactually attempt

an <acronym>SSL</>

connection.<indexterm><primary>SSL</><secondary

sortas="libpq">with libpq</></indexterm>