在 DigitalOcean 上升级我的 debian（测试，jessie 到拉伸）服务器后，MariaDB 不会以服务 mariadb start 启动。
我试图清除所有 mariadb-* 和 mysql-* 包，删除配置和数据，然后重新安装它们，但 mariadb-server-10.1.21-5 拒绝配置：
Setting up mariadb-server-10.1 (10.1.21-5) ...
Job for mariadb.service failed because the control process exited with error code.
See "systemctl status mariadb.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
? mariadb.service - MariaDB database server
Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Thu 2017-02-09 21:25:27 CET; 10ms ago
Process: 1696 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION …