linux下程序JDBC连接不到mysql数据库

　　今天在linux下部署一个 JavaEE项目的时候总是连接不到Mysql数据库，检查之后发现连接池的配置确定是对的，进入linux服务器之后以mysql -uname -ppassword连接总是报Access denied for user 'root'@'localhost' (using password: YES”)，最终解决掉这个问题之后还是连接不上(参考:http://www.cnblogs.com/qlqwjy/p/8315802.html)。

　　解决掉之后通过在本地的sqlyog连接都报错，可是在linux服务器上可以运行，用下面语句授权之后还是连接不上，并且Java程序也是连接不上

授权:

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

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

mysql> flush privileges;  

 查看登录用户信息:

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

此时用service myqld stop发现不起作用，也就是关不掉mysql服务，用service mysqld start启动报错:

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.

最终通过查看mysql的错误日志发现mysql服务一直开启着:

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

错误日志:

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

解决办法:最后是通过查看mysql相关的pid然后杀死进程之后重新启动mysql解决的:

[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

通过上面命令查看到mysql相关的进程id之后杀掉进程，重启mysql服务发现一切正常。

[root@iz2ze46xi6pjjj69ailg9lz logs]# service mysqld start