今天在linux下部署一個 JavaEE項目的時候總是連接不到Mysql數據庫，檢查之後發現連接池的配置確定是對的，進入linux服務器之後以mysql -uname -ppassword連接總是報Access denied for user ‘root‘@‘localhost‘ (using password: YES”)，最終解決掉這個問題之後還是連接不上(參考:http://www.cnblogs.com/qlqwjy/p/8315802.html)。

　　解決掉之後通過在本地的sqlyog連接都報錯，可是在linux服務器上可以運行，用下面語句授權之後還是連接不上，並且Java程序也是連接不上

授權:

  mysql> grant all privileges on *.* to ‘root‘@‘%‘ identified by ‘admin‘;  

mysql> grant all privileges on *.* to ‘root‘@‘localhost‘ identified by ‘admin‘;  

mysql> flush privileges;  

查看登錄用戶信息:

mysql> select user,host,password  from mysql.user;

此時用service myqld stop發現不起作用，也就是關不掉mysql服務，用service mysqld start啟動報錯:

Starting mysqld (via systemctl):  Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.

最終通過查看mysql的錯誤日誌發現mysql服務一直開啟著:

mysql> show variables like ‘error_log‘;
Empty set (0.00 sec)

mysql
 
> show variables like ‘log_error‘;
+---------------+---------------------+
| Variable_name | Value               |
+---------------+---------------------+
| log_error     | /var/log/mysqld.log |
+---------------+---------------------+
1 row in set (0.00 sec)

mysql> quit
Bye
[root@iz2ze46xi6pjjj69ailg9lz logs]# cat /var/log/mysqld.log

錯誤日誌:

180119 10:01:35 mysqld_safe Logging to ‘/var/log/mysqld.log‘.
180119 10:01:35 mysqld_safe A mysqld process already exists
180119 10:01:37 mysqld_safe Logging to ‘/var/log/mysqld.log‘.
180119 10:01:37 mysqld_safe A mysqld process already exists
180119 10:01:38 mysqld_safe Logging to ‘/var/log/mysqld.log‘.
180119 10:01:38 mysqld_safe A mysqld process already exists

解決辦法:最後是通過查看mysql相關的pid然後殺死進程之後重新啟動mysql解決的:

[root@iz2ze46xi6pjjj69ailg9lz logs]# ps -ef|grep mysql
mysql    24359     1  0 10:31 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe --basedir=/usr
mysql    24541 24359  0 10:31 ?        00:00:01 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock
root     25420 25023  0 11:17 pts/2    00:00:00 grep --color=auto mysql
[root@iz2ze46xi6pjjj69ailg9lz logs]# kill -9 24541
[root@iz2ze46xi6pjjj69ailg9lz logs]# kill -9 24359

通過上面命令查看到mysql相關的進程id之後殺掉進程，重啟mysql服務發現一切正常。

[root@iz2ze46xi6pjjj69ailg9lz logs]# service mysqld start

linux下程序JDBC連接不到mysql數據庫