Call to undefined function mb_strlen()

Error location

FILE: /www/ThinkPhp/Application/Common/Common/function.php LINE: 16

at There is no problem running in wnmp environment. This problem occurred when I uploaded the website to the Alibaba Cloud server and the environment was lnmp: centos6.8 nginx mysql5.7 php5.4.

Cause: The display page in the view folder under the thinkphp framework uses the custom function msubstr. This function calls mb_strlen, so this problem occurs.

I removed this function msubstr from the display page and it was fine.

I would like to ask if the extension module is not enabled under the centos system? I have tried all the methods mentioned on the internet but to no avail.