From the log after systemctl restart mariadb.service:
InnoDB: wrong number of columns in SYS_INDEXES record 151124 9:51:40 [Note] InnoDB: Percona XtraDB (http://www.percona.com) 5.6.25-73.1 started; log sequence number 583845802 151124 9:51:40 [Note] Plugin 'FEEDBACK' is disabled. InnoDB: wrong number of columns in SYS_INDEXES record 151124 9:51:40 [Warning] InnoDB: Cannot open table mysql/plugin from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 151124 9:51:40 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it. InnoDB: wrong number of columns in SYS_INDEXES record 151124 9:51:40 [Warning] InnoDB: Cannot open table mysql/servers from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 151124 9:51:40 [ERROR] Can't open and lock privilege tables: Table 'mysql.servers' doesn't exist in engine 151124 9:51:40 [Note] Server socket created on IP: '::'. 151124 9:51:40 [ERROR] Fatal error: mysql.user table is damaged or in unsupported 3.20 format. 151124 09:51:40 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended Trying other things [root@tiger ~]# mysqld_safe -uroot 151124 10:24:03 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'. 151124 10:24:03 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 151124 10:24:03 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended [root@tiger ~]# mysql_upgrade Version check failed. Got the following error when calling the 'mysql' command line client ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2 "No such file or directory") FATAL ERROR: Upgrade failed [root@tiger ~]#