通常，MySQL将错误日志输出在hostname.err文件中，但MySQL5.7可以将错误日志打印到操作系统日志中，具体操作如下：
MySQL服务器启动的时候，mysqld_safe加 --syslog参数，如下：
启动MySQL服务：
[root@mysql log]# /usr/local/mysql/bin/mysqld_safe --defaults-file=/etc/my.cnf --syslog --user=mysql &
[1] 17994
[root@mysql log]# 2017-07-21T04:05:12.802731Z mysqld_safe Logging to syslog.
2017-07-21T04:05:12.807548Z mysqld_safe Logging to '/var/log/mysqld.log'.
2017-07-21T04:05:12.828189Z mysqld_safe Starting mysqld daemon with databases from /mysql/data
[root@mysql log]#

查看系统日志：
[root@mysql log]# tail -f /var/log/messages
Jul 21 12:05:14 mysql mysqld[18451]: Server hostname (bind-address): '*'; port: 3306
Jul 21 12:05:14 mysql mysqld[18451]: IPv6 is available.
Jul 21 12:05:14 mysql mysqld[18451]:- '::' resolves to '::';
Jul 21 12:05:14 mysql mysqld[18451]: Server socket created on IP: '::'.
Jul 21 12:05:14 mysql mysqld[18451]: Event Scheduler: Loaded 0 events
Jul 21 12:05:14 mysql mysqld[18451]: /usr/local/mysql/bin/mysqld: ready for connections.#012Version: '5.7.18-log' socket: '/tmp/mysqld.sock' port: 3306 Source distribution
Jul 21 12:05:14 mysql mysqld[18451]: Executing 'SELECT * FROM INFORMATION_SCHEMA.TABLES;' to get a list of tables using the deprecated partition engine. You may use the startup option '--disable-partition-engine-check' to skip this check.
Jul 21 12:05:14 mysql mysqld[18451]: Beginning of list of non-natively partitioned tables
Jul 21 12:05:14 mysql mysqld[18451]: End of list of non-natively partitioned tables
Jul 21 12:05:14 mysql mysqld[18451]: InnoDB: Buffer pool(s) load completed at 170721 12:05:14