How to add PHP extensions in CentOS 7. Search and then install.
https://stackoverflow.com/questions/28739892/centos-7-cant-install-php-mbstring-extension/51432841
cat /etc/redhat-release && php -v && yum search mbstring ========================================================================= N/S matched: mbstring ========================================================================== ea-php54-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php55-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php56-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php70-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php71-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php72-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling ea-php73-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling
Then install. Don’t forget to change to your version and module.
sudo yum install ea-php71-php-mbstring