For PHP 7 and Ubuntu 14.04 the procedure is follows. Since PHP 7 is not in the official Ubuntu PPAs you likely installed it through Ondřej Surý’s PPA (sudo add-apt-repository ppa:ondrej/php). Go to /etc/php/7.0/ edit php.ini, uncomment to following line:
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extension=php_xmlrpc.dll
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Then simply install php7.0-xml:
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sudo apt-get install php7.0-xml
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And restart Apache:
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sudo /etc/init.d/apache restart
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