Mysql Job failed to start

I got an error while am up starting the mysql service.

/etc/init.d/mysql start
Rather than invoking init scripts through /etc/init.d, use the service(8)
utility, e.g. service mysql start

Since the script you are attempting to invoke has been converted to an
Upstart job, you may also use the start(8) utility, e.g. start mysql
start: Job failed to start

    First, try to reboot the server (if it doesn't work, follow to the next steps):
       

sudo reboot

    Other steps:
        First, create a backup from you MySQL folder var/lib/mysql/, just to make sure your data will be safe:

        sudo -i
        cp -R /var/lib/mysql/ ~/mysql

    After that, remove/purge MySQL (this will remove: php5-mysql, phpmyadmin and other libraries, so after the procedure, you will have to reinstall again.

        sudo apt-get purge mysql-server-5.1 mysql-common

    Remove the folder /etc/mysql/ and its content:

        sudo rm /etc/mysql/ -R

    Later on, check if the database files are still in the folder /var/lib/mysql/ and if they are not, then copy it back:

        mkdir /var/lib/mysql/
        chown root:root /var/lib/mysql/ -R
        cd ~/mysql/
        cp * /var/lib/mysql/ -R

    Okay, then install o mysql server again

        apt-get install mysql-server

    And finally install phpmyadmin and php5-mysql:

        apt-get install php5-mysql
        apt-get install phpmyadmin

    At last, restart the services and check if the status are okay now:

        service apache2 restart
        service mysql restart

That's it! It should work. I hope it works for you! (don't worry about the old data.That's why we have backup it first)

mysql报错：

ERROR 3009 (HY000): Column count of mysql.user is wrong. Expected 45, found 42. Created with MySQL 50554, now running 50719. Please use mysql_upgrade to fix this error

错误是由于你曾经升级过数据库，升级完后没有使用
mysql_upgrade升级数据结构造成的。
解决办法：
使用mysql_upgrade命令

root@localhost ~]# mysql_upgrade -u root -p 13456