Para ativar as extensões, verifique se elas estão ativadas nesses arquivos .ini
arquivos:
/etc/php/5.6/cli/php.ini
/etc/php/5.6/cli/conf.d/10-mysqlnd.ini
/etc/php/5.6/cli/conf.d/10-opcache.ini
/etc/php/5.6/cli/conf.d/10-pdo.ini
/etc/php/5.6/cli/conf.d/20-calendar.ini
/etc/php/5.6/cli/conf.d/20-ctype.ini
/etc/php/5.6/cli/conf.d/20-exif.ini
/etc/php/5.6/cli/conf.d/20-fileinfo.ini
/etc/php/5.6/cli/conf.d/20-ftp.ini
/etc/php/5.6/cli/conf.d/20-gettext.ini
/etc/php/5.6/cli/conf.d/20-iconv.ini
/etc/php/5.6/cli/conf.d/20-json.ini
/etc/php/5.6/cli/conf.d/20-mbstring.ini
/etc/php/5.6/cli/conf.d/20-mysql.ini
/etc/php/5.6/cli/conf.d/20-mysqli.ini
/etc/php/5.6/cli/conf.d/20-pdo_mysql.ini
/etc/php/5.6/cli/conf.d/20-phar.ini
/etc/php/5.6/cli/conf.d/20-posix.ini
/etc/php/5.6/cli/conf.d/20-readline.ini
/etc/php/5.6/cli/conf.d/20-shmop.ini
/etc/php/5.6/cli/conf.d/20-sockets.ini
/etc/php/5.6/cli/conf.d/20-sysvmsg.ini
/etc/php/5.6/cli/conf.d/20-sysvsem.ini
/etc/php/5.6/cli/conf.d/20-sysvshm.ini
/etc/php/5.6/cli/conf.d/20-tokenizer.ini
sudo a2enmode reescrever - algo que eu fiz Agora começou - /etc/php/7.0/cli/php.ini
/etc/php/7.0/cli/conf.d/10-mysqlnd.ini
/etc/php/7.0/cli/conf.d/10-opcache.ini
Como habilitar extensões php5.6..cuidadamente me ajude a resolver ??
isto está vindo quando executar o comando "composer update" na pasta laravel.