访问主页
突然出现问题：
Safari无法访问
试了试chrome可以
以及是翻墙的原因，结果全局翻墙，Safari还是无法访问：
Safari 浏览器无法打开页面 “https://www.crifan.com/”。 错误是：“FetchEvent.respondWith received an error: Returned response is null.” (WebKitServiceWorker:0)
然后去Chrome中打开某个具体页面，发现有问题：
无法打开：
想要进入后台，结果显示
建立数据库连接时出错 这意味着您在wp-config.php文件中指定的用户名和密码信息不正确，或我们未能在localhost联系到数据库服务器。这可能意味着您主机的数据库服务器未在运行。 * 您确定用户名和密码正确吗？ * 您确定输入的主机名正确吗？ * 您确定数据库服务器在运行吗？
如果您不明白这些意味着什么，您应该联系您的主机提供商。如果您仍需要帮助，请访问WordPress支持论坛。
感觉像是服务器中mysql数据库挂了？
去看看
Last failed login: Thu Oct 17 10:39:31 CST 2019 from 61.28.227.133 on ssh:notty There were 134679 failed login attempts since the last successful login. Last login: Wed Jul 31 10:31:54 2019 from 222.92.130.218 [root@crifan ~]#
登录后台
centos check mysql
HowTo: Find out If MySQL Is Running On Linux Or Not – nixCraft
mysqladmin -u root -p status
结果：
[root@crifan ~]# mysqladmin -u root -p status Enter password: mysqladmin: connect to server at 'localhost' failed error: 'Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)' Check that mysqld is running and that the socket: '/tmp/mysql.sock' exists!
Show (List) MySQL Databases on Linux via Command Line | Liquid Web
[root@crifan ~]# mysql -u root -p Enter password: ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
How do You Know if MySQL is Running on CentOS 7?
[root@crifan ~]# top | grep mysql
[root@crifan ~]#
另外：
[root@crifan ~]# systemctl status mysqld ● mysqld.service - LSB: start and stop MySQL Loaded: loaded (/etc/rc.d/init.d/mysqld; bad; vendor preset: disabled) Active: active (exited) since Wed 2019-07-31 10:30:10 CST; 2 months 17 days ago Docs: man:systemd-sysv-generator(8) Process: 2999 ExecStart=/etc/rc.d/init.d/mysqld start (code=exited, status=0/SUCCESS)
Oct 16 05:20:26 crifan.com mysqld[2999]: /usr/local/mysql/bin/mysqld_safe: line 199: 4057 Killed nohup /usr/local/mysql/bin/mysqld –basedir=/usr/l…
Oct 16 05:43:06 crifan.com mysqld[2999]: /usr/local/mysql/bin/mysqld_safe: line 199: 13049 Killed nohup /usr/local/mysql/bin/mysqld –basedir=/usr/l…
Oct 16 05:43:31 crifan.com mysqld[2999]: /usr/local/mysql/bin/mysqld_safe: line 199: 13452 Killed nohup /usr/local/mysql/bin/mysqld –basedir=/usr/l…
Hint: Some lines were ellipsized, use -l to show in full.
感觉是：
已经退出了。
那强制关闭再启动
[root@crifan ~]# systemctl stop mysqld [root@crifan ~]# systemctl start mysqld [root@crifan ~]# systemctl status mysqld ● mysqld.service - LSB: start and stop MySQL Loaded: loaded (/etc/rc.d/init.d/mysqld; bad; vendor preset: disabled) Active: active (running) since Thu 2019-10-17 10:45:36 CST; 3s ago Docs: man:systemd-sysv-generator(8) Process: 405 ExecStop=/etc/rc.d/init.d/mysqld stop (code=exited, status=0/SUCCESS) Process: 442 ExecStart=/etc/rc.d/init.d/mysqld start (code=exited, status=0/SUCCESS) CGroup: /system.slice/mysqld.service ├─ 455 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/data/mysql --pid-file=/data/mysql/mysql.pid └─1306 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/data/mysql --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/dat...
Oct 17 10:45:34 crifan.com systemd[1]: Starting LSB: start and stop MySQL…
Oct 17 10:45:36 crifan.com mysqld[442]: Starting MySQL..[ OK ]
Oct 17 10:45:36 crifan.com systemd[1]: Started LSB: start and stop MySQL.
再去访问访问看看
就正常了：
【总结】
此处访问crifan.com的WordPress网站出现
建立数据库连接时出错
原因是：
mysql数据库（异常）退出了
但是什么原因导致退出的，不知道。
解决办法：
重新启动
systemctl stop mysqld systemctl start mysqld
然后通过：
systemctl status mysqld
确认状态是：
active (running)
即可。
另外：
systemctl status mysqld <p>...</p><p> Active: active (exited) since Wed 2019-07-31 10:30:10 CST; 2 months 17 days ago</p>
看到是：
之前异常状态
active (exited) = 有效但是却退出了的
难道是 2个多月之前就出现了？
那最近网站貌似没什么问题的，只是这几天出现问题的。
难道是是 mysql状态是 active (exited)，也都可以正常运行（很长时间）？
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