I opened some some ini files like mysqli.ini , mysql.ini , pdo_mysql.ini. Inside those files there is an .so extension added for those files. I want to know where these .so files are stored.
Inside mysqli.ini file
; configuration for php MySQL module
; priority=20
extension=mysqli.so
Inside mysql.ini file
; configuration for php MySQL module
; priority=20
extension=mysql.so
Inside pdo_mysql.ini file
; configuration for php MySQL module
; priority=20
extension=pdo_mysql.so
The .so files should be located inside your php extension directory.
You can use phpinfo() function to find the location of your php extension directory or you can use php -i from the command line.
Example
root@73fa7795de48:/# php -i | grep extension_dir
extension_dir => /usr/lib/php/20160303 => /usr/lib/php/20160303