今天使用CentOS7安裝mysql後，啟動時出現了一個問題，折騰了一下午才弄好。問題如下：
啟動時報錯：Starting MySQL. ERROR! The server quit without updating PID file (/data/mysql/localhost.localdomain.pid)。
網上找了很多資料，能試的方式都用了，還是不行，最後自己瞎折騰出來了。解決方法如下：

1.通過安全模式啟動mysql
[[email protected] scripts]# /usr/local/mysql/bin/mysqld_safe --user=mysql &
此時應該會報錯：
 

[1] 34419
[[email protected] 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: 無法建立"/var/log/mariadb/mariadb.log"
 
: 沒有那個檔案或目錄
chmod: 無法訪問"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
touch: 無法建立"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
chown: 無法訪問"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
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: 沒有那個檔案或目錄
/usr/local
 
/mysql/bin/mysqld_safe:行165: /var/log/mariadb/mariadb.log: 沒有那個檔案或目錄
touch: 無法建立"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
chown: 無法訪問"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
chmod: 無法訪問"/var/log/mariadb/mariadb.log": 沒有那個檔案或目錄
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: 沒有那個檔案或目錄
^C
[1]+  退出 1                /usr/local/mysql/bin/mysqld_safe --user=mysql

2.手動建立mariadb目錄，並再次通過安全模式啟動。

[[email protected] scripts]# mkdir /var/log/mariadb
[[email protected] scripts]# /usr/local/mysql/bin/mysqld_safe --user=mysql &
[1] 34743
[[email protected] 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.然後啟動mysql

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

OK！啟動成功。為什麼要先啟動安全模式，我也不知道，我是小菜。有知道的大神麻煩告知一下，謝謝啦！