CentOS7安装mysql5.5 启动出错 The server quit without updating PID file……

今天使用CentOS7安装mysql后，启动时出现了一个问题，折腾了一下午才弄好。问题如下：
启动时报错：Starting MySQL. ERROR! The server quit without updating PID file (/data/mysql/localhost.localdomain.pid)。
网上找了很多资料，能试的方式都用了，还是不行，最后自己瞎折腾出来了。解决方法如下：

1.通过安全模式启动mysql
[root@localhost scripts]# /usr/local/mysql/bin/mysqld_safe --user=mysql &
此时应该会报错：

[1] 34419
[root@localhost scripts]# 170730 03:06:58 mysqld_safe WARNING: Found /data/mysql/my.cnf
The data directory is a deprecated location for my.cnf, please move it to
/usr/local/product/mysql5.5.49/my.cnf
170730 03:06:59 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
touch: 无法创建"/var/log/mariadb/mariadb.log": 没有那个文件或目录
chmod: 无法访问"/var/log/mariadb/mariadb.log": 没有那个文件或目录
touch: 无法创建"/var/log/mariadb/mariadb.log": 没有那个文件或目录
chown: 无法访问"/var/log/mariadb/mariadb.log": 没有那个文件或目录
170730 03:06:59 mysqld_safe Starting mysqld daemon with databases from /data/mysql
/usr/local/mysql/bin/mysqld_safe:行128: /var/log/mariadb/mariadb.log: 没有那个文件或目录
/usr/local/mysql/bin/mysqld_safe:行165: /var/log/mariadb/mariadb.log: 没有那个文件或目录
touch: 无法创建"/var/log/mariadb/mariadb.log": 没有那个文件或目录
chown: 无法访问"/var/log/mariadb/mariadb.log": 没有那个文件或目录
chmod: 无法访问"/var/log/mariadb/mariadb.log": 没有那个文件或目录
170730 03:06:59 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended
/usr/local/mysql/bin/mysqld_safe:行128: /var/log/mariadb/mariadb.log: 没有那个文件或目录
^C
[1]+  退出 1                /usr/local/mysql/bin/mysqld_safe --user=mysql

2.手动创建mariadb目录，并再次通过安全模式启动。

[root@localhost scripts]# mkdir /var/log/mariadb
[root@localhost scripts]# /usr/local/mysql/bin/mysqld_safe --user=mysql &
[1] 34743
[root@localhost scripts]# 170730 03:09:28 mysqld_safe WARNING: Found /data/mysql/my.cnf
The data directory is a deprecated location for my.cnf, please move it to
/usr/local/product/mysql5.5.49/my.cnf
170730 03:09:28 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
170730 03:09:28 mysqld_safe Starting mysqld daemon with databases from /data/mysql
170730 03:09:30 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended

[1]+  完成                  /usr/local/mysql/bin/mysqld_safe --user=mysql

3.然后启动mysql

[root@localhost scripts]# /etc/init.d/mysqld start
Starting MySQL... SUCCESS! 

OK！启动成功。为什么要先启动安全模式，我也不知道，我是小菜。有知道的大神麻烦告知一下，谢谢啦！