Corrigindo o erro: The gmp or bcmath extension must be installed to read this database

Instale o pacote gmp:

sudo apt install php7.0-gmp

Instale o pacote bcmath:

sudo apt install php7.0-bcmath

Reinicie o apache:

sudo service apache2 restart

Fonte:

• https://www.php.net/manual/pt_BR/book.bc.php
• https://www.php.net/manual/pt_BR/book.gmp.php