我无法在Centos 7上安装mbstring。运行命令yum install php-mbstring时出错。
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.cogentco.com
* epel: mirror.symnds.com
* extras: mirror.ash.fastserv.com
* remi-safe: mirrors.mediatemple.net
* updates: mirror.vtti.vt.edu
No package php-mbstring available.
Error: Nothing to do