Startup: Unable to load dynamic library '/usr/lib/php/20151012/php_mbstring.dll

When I run the command

php -v

this error comes up in ubuntu terminall:

PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/lib/php/20151012/php_mbstring.dll' - /usr/lib/php/20151012/php_mbstring.dll: cannot open shared object file: No such file or directory in Unknown on line 0

Your configuration is wrong. You (or some software you have installed) have enabled something like:

extension=php_mbstring.dll

in the PHP configuration file, and this is wrong as php_mbstring.dll is an extension compiled for Windows operating system.

The correct way is to install php-mbstring package and let it enable the mbstring extension automatically:

sudo apt-get install php-mbstring

You can then disable/enable the extension by using phpenmod/phpdismod commands:

sudo phpdismod mbstring # disable mbstring extension
sudo phpenmod mbstring # enable mbstring extension again

I am Running Ubuntu 16.04 with PHP5.X - PHP7

when I installed php7 i started to get this error with /usr/lib/php/sessionclean

to fix this I had to comment out in /etc/php/7.0/apache2/php.ini the offending extensions line, which by default were .dll

extension=mbstring.dll

to

;extension=php_mbstring.dll