Vesta Control Panel, PHP 5.3 Downgrade işlemi aşağıdaki gibi yapabilirsiniz.

service httpd stop
yum -y remove php*
yum -y install php php-bcmath php-cli php-common php-gd php-imap php-mbstring php-mcrypt php-mysql php-pdo php-soap php-tidy php-xml php-xmlrpc php-pecl-apc phpMyAdmin roundcubemail
mv -f /etc/php.ini.rpmsave /etc/php.ini
mv -f /etc/roundcubemail/db.inc.php.rpmsave /etc/roundcubemail/db.inc.php
mv -f /etc/roundcubemail/main.inc.php.rpmsave /etc/roundcubemail/main.inc.php
mv -f /etc/phpMyAdmin/config.inc.php.rpmsave /etc/phpMyAdmin/config.inc.php
mv -f /etc/httpd/conf.d/roundcubemail.conf.rpmsave /etc/httpd/conf.d/roundcubemail.conf
mv -f /etc/httpd/conf.d/phpMyAdmin.conf.rpmsave /etc/httpd/conf.d/phpMyAdmin.conf
service httpd start

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