ubuntu 14.04 安装 mysql-server 及 可能出现的有关问题（Unknow job: mysql）和解决方法
一、安装mysql
在终端键入如下命令：
(sudo) apt-get install mysql-server
安装过程中，会出现 configuration 界面，提示用户设置 MySQL root user 的密码。
如果安装成功， MySQL server 会自动启动。通过在终端键入如下命令， 查看 MySQL server 是否正在运行
(sudo) netstat -tap | grep mysql
如果 MySQL Server 正在运行，则终端会显式如下内容：
如果 MySQL Server 没有正确运行，在终端键入如下命令：
(sudo) service restart
二、可能出现的问题，如果安装过程中，终端出现如下提示：
initctl：Unknown job：mysql
则安装结束后，将无法启动 mysql。如下图所示：
出现这一问题，跟 mysql 没有直接关系， 而是由于初始守护进程控制工具（The init daemon control tool）没有使 mysql server daemon 从 /etc/init 启动。可以在终端键入如下命令手动恢复：
(sudo) initctl reload-configuration
附：
Configuration
You can edit the /etc/mysql/my.cnf file to configure the basic settings -- log file, port number, etc. For example, to configure MySQL to listen for connections from network hosts, change the bind-address directive to the server's IP address:
bind-address = 192.168.0.5
Replace 192.168.0.5 with the appropriate address.
After making a change to /etc/mysql/my.cnf the MySQL daemon will need to be restarted:
sudo service mysql restart
If you would like to change the MySQL root password, in a terminal enter:
sudo dpkg-reconfigure mysql-server-5.5
The MySQL daemon will be stopped, and you will be prompted to enter a new password.
Database Engines
Whilst the default configuration of MySQL provided by the Ubuntu packages is perfectly functional and performs well there are things you may wish to consider before you proceed.
MySQL is designed to allow data to be stored in different ways. These methods are referred to as either database or storage engines. There are two main engines that you'll be interested in: InnoDB and MyISAM. Storage engines are transparent to the end user. MySQL will handle things differently under the surface, but regardless of which storage engine is in use, you will interact with the database in the same way.
Each engine has its own advantages and disadvantages.
While it is possible, and may be advantageous to mix and match database engines on a table level, doing so reduces the effectiveness of the performance tuning you can do as you'll be splitting the resources between two engines instead of dedicating them to one.
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MyISAM is the older of the two. It can be faster than InnoDB under certain circumstances and favours a read only workload. Some web applications have been tuned around MyISAM (though that's not to imply that they will slow under InnoDB). MyISAM also supports the FULLTEXT data type, which allows very fast searches of large quantities of text data. However MyISAM is only capable of locking an entire table for writing. This means only one process can update a table at a time. As any application that uses the table scales this may prove to be a hindrance. It also lacks journaling, which makes it harder for data to be recovered after a crash. The following link provides some points for consideration about using MyISAM on a production database.
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InnoDB is a more modern database engine, designed to be ACID compliant which guarantees database transactions are processed reliably. Write locking can occur on a row level basis within a table. That means multiple updates can occur on a single table simultaneously. Data caching is also handled in memory within the database engine, allowing caching on a more efficient row level basis rather than file block. To meet ACID compliance all transactions are journaled independently of the main tables. This allows for much more reliable data recovery as data consistency can be checked.
As of MySQL 5.5 InnoDB is the default engine, and is highly recommended over MyISAM unless you have specific need for features unique to the engine.
Advanced configuration
Creating a tuned my.cnf file
There are a number of parameters that can be adjusted within MySQL's configuration file that will allow you to improve the performance of the server over time. For initial set-up you may find Percona's my.cnf generating tool useful. This tool will help generate a my.cnf file that will be much more optimised for your specific server capabilities and your requirements.
Do not replace your existing my.cnf file with Percona's one if you have already loaded data into the database. Some of the changes that will be in the file will be incompatible as they alter how data is stored on the hard disk and you'll be unable to start MySQL. If you do wish to use it and you have existing data, you will need to carry out a mysqldump and reload:
mysqldump --all-databases --routines -u root -p > ~/fulldump.sql
Once the dump has been completed, shut down MySQL:
sudo service mysql stop
sudo cp /etc/mysql/my.cnf /etc/mysql/my.cnf.backup sudo cp /path/to/new/my.cnf /etc/mysql/my.cnf
sudo rm -rf /var/lib/mysql/* sudo mysql_install_db sudo chown -R mysql: /var/lib/mysql sudo service mysql start
sudo apt-get install pv pv ~/fulldump.sql | mysql
This is not necessary for all my.cnf changes. Most of the variables you may wish to change to improve performance are adjustable even whilst the server is running. As with anything, make sure to have a good backup copy of config files and data before making changes.
MySQL Tuner
MySQL Tuner is a useful tool that will connect to a running MySQL instance and offer suggestions for how it can be best configured for your workload. The longer the server has been running for, the better the advice mysqltuner can provide. In a production environment, consider waiting for at least 24 hours before running the tool. You can get install mysqltuner from the Ubuntu repositories:
sudo apt-get install mysqltuner
mysqltuner
-------- Recommendations -----------------------------------------------------
General recommendations:
Run OPTIMIZE TABLE to defragment tables for better performance
Increase table_cache gradually to avoid file descriptor limits
Variables to adjust:
key_buffer_size (> 1.4G)
query_cache_size (> 32M)
table_cache (> 64)
innodb_buffer_pool_size (>= 22G)
One final comment on tuning databases: Whilst we can broadly say that certain settings are the best, performance can vary from application to application. For example, what works best for Wordpress might not be the best for Drupal, Joomla or proprietary applications. Performance is dependent on the types of queries, use of indexes, how efficient the database design is and so on. You may find it useful to spend some time searching for database tuning tips based on what applications you're using it for. Once you get past a certain point any adjustments you make will only result in minor improvements, and you'll be better off either improving the application, or looking at scaling up your database environment through either using more powerful hardware or by adding slave servers.