Установка

The socket functions described here are part of an extension to PHP which must be enabled at compile time by giving the --enable-sockets option to configure.

Замечание: Поддержка IPv6 была добавлена в PHP 5.0.0.

Коментарии

At the time of writing, most Linux distributions ship their PHP versions with sockets enabled by default. 
Tested distros/versions: 

CentOS 7, PHP 5.4: Enabled;
CentOS 7, Remi repo, PHP 7.1.1: Enabled;
CentOS 7, DirectAdmin Custombuild, PHP 7.0.9: Enabled;
CentOS 7, DirectAdmin Custombuild, PHP 5.6.24: Enabled;
Debian Jessie, PHP 5.6.30-0+deb8u1: Enabled;
Gentoo Linux ~amd64, PHP 7.1.1: Enabled (USE-flag "sockets" is enabled by default)

Alpine Linux: PHP 5.6.30: Disabled, however this can simply be enabled by installing php5-sockets

I haven't tested other distros/versions, but as far as compatibility goes most systems seem to support sockets out of the box.
2017-02-17 15:05:25
http://php5.kiev.ua/manual/ru/sockets.installation.html

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