环境:

[root@localhost php.d]# cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)
[root@localhost php.d]# php -v
PHP 7.2.10 (cli) (built: Sep 15 2018 07:10:58) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologieswith Xdebug v2.6.0, Copyright (c) 2002-2018, by Derick Rethans

为php安装event扩展，搜索下：yum search php | grep event

[root@localhost php.d]# yum search php | grep event
php-evenement.noarch : Événement is a very simple event dispatching library for
php-ezc-EventLog.noarch : Allows you to log events or audit trails
php-kdyby-events.noarch : Events for Nette Framework
php-pecl-event.x86_64 : Provides interface to libevent library
php-react-event-loop.noarch : Event loop abstraction layer that libraries can: use for evented I/O
php-react-http.noarch : Library for building an evented http server
php-sabre-event.noarch : Lightweight library for event-based programming
php-symfony-event-dispatcher.noarch : Symfony EventDispatcher Component

感觉没有合适的包，改用: pecl search event搜索, 找到了event和libevent包，我选择安装event

安装: pecl install event

安装完成后，将"extension=event.so"加入php.ini文件，但是遇到了标题中描述的错误，如下：

[root@localhost php.d]# php -m
PHP Warning:  PHP Startup: Unable to load dynamic library 'event.so' (tried: /usr/lib64/php/modules/event.so (/usr/lib64/php/modules/event.so: undefined symbol: php_sockets_le_socket), /usr/lib64/php/modules/event.so.so (/usr/lib64/php/modules/event.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
[PHP Modules]

修改：sockets.ini, 如下：

[root@localhost php.d]# cat sockets.ini
; Enable sockets extension module
extension=sockets.so
extension=event.so

问题解决，似乎是加载顺序导致的！因为event.so依赖于sockets.so！