Centos – `GLIBCXX_3.4.20′ not found Centos7

Dlls (Dynamic Loadable Library) is being used only in Windows. For Linux (and BSD and probably most of unix-like OS'es) you have .so (shared object) instead. You probably need to change .dll to .so in php.ini or one of files included in it (it may be something like /etc/php.d/mbstring.ini or something similar).

Also, you can find path of .so file by running rpm -ql php-mbstring - it will list all files belonging to package.

The two repos, remi and mysql56-community, cannot be used together because they are using incompatible package naming schemes. yum info mysql will not show anything from the MySQL community repo because none of the packages is named mysql under the new naming scheme. Try yum info mysql\* instead.

Consequently, you cannot update MySQL directly from Remi to the MySQL community repo. Instead, you need to follow MySQL's instructions for replacing a third party distribution of MySQL, specifically the section on "Nonnative Third-Party Distributions". This involves uninstalling the Remi packages and then installing the MySQL community packages by their new names.

If you need to keep the Remi repo for other packages you should make sure that yum won't use its MySQL packages anymore by adding either exclude=mysql* or an appropriate includepkgs line to the repo definition.