'Where are php's extensions .so files located?

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


Solution 1:[1]

On Linux system

php -i | grep extension_dir  | cut -d " " -f 5

will display you the current php extension dir

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Your Common Sense