Thank you very much for your help.
First, I upgraded the version of MariaDB. I followed that tutorial where that is pretty well explained : http://www.tecmint.com/upgrade-mariadb-5-5-to-10-centos-rhel-debian-ubuntu/
Then, I installed again these packages :
# yum install php-mysql
# yum install php-pdo
Finally, I followed your advice. I edited the /etc/my.cnf file and I added what you just wrote down.
For the TimeZone issue, I changed the /etc/php.ini file. You normally have :
; Defines the default timezone used by the date functions
That part was empty for me. I uncommented the line ";date.timezone = " and changed it :
date.timezone = Europe/Paris
Now I have to find out how to populate that Timezone.
Thank you very much for your time, hope that will help some people