title: Centos7 mysql can not start
body: <p>Now I want to start mysql use <code>service mysqld start</code> on centos7,but I got the follow error:<br>
  OS: centos64 bit</p>
  
  <pre><code>Redirecting to /bin/systemctl start mysqld.service Job for mysqld.service failed.   
  See 'systemctl status mysqld.service andjournalctl -xn for details.
  </code></pre>
  
  <p>the follow had been installed without any error and warning:</p>
  
  <pre><code>mysql-community-bench-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-client-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-common-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-devel-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-embedded-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-embedded-devel-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-libs-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-release-el7-5.noarch.rpm
  mysql-community-server-5.7.5-0.6.m15.el7.x86_64.rpm
  mysql-community-test-5.7.5-0.6.m15.el7.x86_64.rpm
  </code></pre>
  
  <p>systemctl -l status mysqld.service</p>
  
  <pre><code>[root@www mysql]# systemctl -l status mysqld.service
  mysqld.service - MySQL Community Server
     Loaded: loaded (/usr/lib/systemd/system/mysqld.service; disabled)
     Active: activating (start-post) since Sun 2015-02-15 03:25:32 EST; 59s ago
    Process: 29844 ExecStart=/usr/bin/mysqld_safe (code=exited, status=0/SUCCESS)
    Process: 29833 ExecStartPre=/usr/bin/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
   Main PID: 29844 (code=exited, status=0/SUCCESS);         : 29845 (mysql-systemd-s)
     CGroup: /system.slice/mysqld.service
             `-control
               |-29845 /bin/bash /usr/bin/mysql-systemd-start post
               `-30168 sleep 1
  
  Feb 15 03:25:32 www mysqld_safe[29844]: 150215 03:25:32 mysqld_safe Logging to '/var/log/mysqld.log'.
  Feb 15 03:25:32 www mysqld_safe[29844]: 150215 03:25:32 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  Feb 15 03:25:32 www mysqld_safe[29844]: /usr/bin/mysqld_safe: line 164: 29987 Killed                  nohup /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 &lt; /dev/null &gt;&gt; /var/log/mysqld.log 2&gt;&amp;1
  Feb 15 03:25:32 www mysqld_safe[29844]: 150215 03:25:32 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  </code></pre>
  
  <p>journalctl -xn</p>
  
  <pre><code>[root@www mysql]# journalctl -xn
  -- Logs begin at Sat 2015-02-14 22:04:13 EST, end at Sun 2015-02-15 03:46:01 EST. --
  Feb 15 03:45:32 www systemd[1]: mysqld.service holdoff time over, scheduling restart.
  Feb 15 03:45:32 www systemd[1]: Stopping MySQL Community Server...
  -- Subject: Unit mysqld.service has begun shutting down
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit mysqld.service has begun shutting down.
  Feb 15 03:45:32 www systemd[1]: Starting MySQL Community Server...
  -- Subject: Unit mysqld.service has begun with start-up
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit mysqld.service has begun starting up.
  Feb 15 03:45:32 www mysqld_safe[1286]: 150215 03:45:32 mysqld_safe Logging to '/var/log/mysqld.log'.
  Feb 15 03:45:32 www mysqld_safe[1286]: 150215 03:45:32 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  Feb 15 03:45:33 www mysqld_safe[1286]: /usr/bin/mysqld_safe: line 164:  1429 Killed                  nohup /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 &lt; /dev/nu
  Feb 15 03:45:33 www mysqld_safe[1286]: 150215 03:45:33 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  Feb 15 03:46:01 www systemd[1]: Starting Session 2660120 of user root.
  -- Subject: Unit session-2660120.scope has begun with start-up
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit session-2660120.scope has begun starting up.
  Feb 15 03:46:01 www systemd[1]: Started Session 2660120 of user root.
  -- Subject: Unit session-2660120.scope has finished start-up
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit session-2660120.scope has finished starting up.
  -- 
  -- The start-up result is done.
  Feb 15 03:46:01 www CROND[1522]: (root) CMD (run-parts /etc/cron.hourly)
  </code></pre>
  
  <p>cat /var/log/mysqld.log</p>
  
  <pre><code>[root@www mysql]# cat /var/log/mysqld.log
  150213 03:00:56 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  150213 03:00:57 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  150213 03:10:55 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  150213 03:10:56 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  150213 03:20:55 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  150213 03:20:55 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  150213 03:30:55 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
  150213 03:30:55 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
  </code></pre>
  
  <p>Whats wrong?</p>