ubuntu，mysql更改datadir

Question

我刚刚在新的ubuntu发行版16上安装了Mysql 5.7。 我试图将Mysql Datadir移动到特定的磁盘。我跟着

但是当试图启动mysql时它失败了

mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: inactive (dead) (Result: exit-code) since mer. 2016-08-17 21:08:09 CEST; 10s ago
  Process: 4735 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=1/FAILURE)

août 17 21:08:09 getesa systemd[1]: mysql.service: Unit entered failed state.
août 17 21:08:09 getesa systemd[1]: mysql.service: Failed with result 'exit-code'.
août 17 21:08:09 getesa systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
août 17 21:08:09 getesa systemd[1]: Stopped MySQL Community Server.
août 17 21:08:09 getesa systemd[1]: mysql.service: Start request repeated too quickly.
août 17 21:08:09 getesa systemd[1]: Failed to start MySQL Community Server.

请帮帮我。