Call to undefined function mb_strlen() on PHP 7 Ubuntu 14.04

Question

I had a Yii installation that was working fine up until today. I installed updates on my machine today after which this error was being thrown on all pages:

PHP Fatal Error – yii\base\ErrorException

Uncaught Error: Call to undefined function yii\web\mb_strlen() in /application/vendor/yiisoft/yii2/web/ErrorHandler.php:404

I ran composer update but the error persists.

I am using yii 2.0.7 on PHP 7 on Ubuntu 14.04. How do I fix this?

Answer 1

The error is a bit of a red herring since mb_strlen() is actually part of the mbstring php extension and not a function in yii2.

In php5 mbstring was part of libapache2-mod-php5.

It seems to be missing from libapache2-mod-php7. To fix this install the php7.x-mbstring package where x is your version:

sudo apt install php7.x-mbstring

You may need to restart Apache after this install.

Answer 2

For PHP7.1

Debian flavours

sudo apt-get install php7.1-mbstring

RedHat flavours

sudo yum install php7.1-mbstring