To install mbstring in Ubuntu/Debian, run the following command:
sudo apt-get install php-mbstring
In CentOS like this:
sudo yum install php-mbstring
You can activate/deactivate the module like this:
sudo phpenmod mbstring sudo phpdismod mbstring
Restart Apache2 to apply the changes:
sudo service apache2 restart
Let’s see if mbstring is activated:
php -i | grep -i mbstring