MySQL - Administration
1) Running and Shutting down MySQL Server
First check if your MySQL server is running or not. You can use the following command to check it −
ps -ef | grep mysqld
If your MySql is running, then you will see mysqld process listed out in your result. If server is not running, then you can start it by using the following command −
root@host# cd /usr/bin
./safe_mysqld &
Now, if you want to shut down an already running MySQL server, then you can do it by using the following command −
root@host# cd /usr/bin
./mysqladmin -u root -p shutdown
Enter password: ******
2) Setting Up a MySQL User Account
For adding a new user to MySQL, you just need to add a new entry to the user table in the database mysql.
The following program is an example of adding a new user guest with SELECT, INSERT and UPDATE privileges with the password guest123; the SQL query is −
root@host# mysql -u root -pEnter password:*******
mysql> use mysql;Database changed
mysql> INSERT INTO user
(host, user, password,
select_priv, insert_priv, update_priv)
VALUES ('localhost', 'guest',
PASSWORD('guest123'), 'Y', 'Y', 'Y');Query OK, 1 row affected (0.20 sec)
mysql> FLUSH PRIVILEGES;Query OK, 1 row affected (0.01 sec)
mysql> SELECT host, user, password FROM user WHERE user = 'guest';+-----------+---------+------------------+| host | user | password |+-----------+---------+------------------+| localhost | guest | 6f8c114b58f2ce9e |+-----------+---------+------------------+1 row in set (0.00 sec)When adding a new user, remember to encrypt the new password using PASSWORD() function provided by MySQL. As you can see in the above example, the password mypass is encrypted to 6f8c114b58f2ce9e.
Notice the FLUSH PRIVILEGES statement. This tells the server to reload the grant tables. If you don't use it, then you won't be able to connect to MySQL using the new user account at least until the server is rebooted.
You can also specify other privileges to a new user by setting the values of following columns in user table to 'Y' when executing the INSERT query or you can update them later using UPDATE query.
Select_priv
Insert_priv
Update_priv
Delete_priv
Create_priv
Drop_priv
Reload_priv
Shutdown_priv
Process_priv
File_priv
Grant_priv
References_priv
Index_priv
Alter_priv
Another way of adding user account is by using GRANT SQL command. The following example will add user zara with password zara123 for a particular database, which is named as TUTORIALS.
root@host# mysql -u root -p password;Enter password:*******
mysql> use mysql;Database changed
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
-> ON TUTORIALS.*-> TO 'zara'@'localhost'-> IDENTIFIED BY 'zara123';This will also create an entry in the MySQL database table called as user.
NOTE − MySQL does not terminate a command until you give a semi colon (;) at the end of the SQL command.
The /etc/my.cnf File Configuration
In most of the cases, you should not touch this file. By default, it will have the following entries −
[mysqld]
datadir = /var/lib/mysql
socket = /var/lib/mysql/mysql.sock
[mysql.server]
user = mysql
basedir = /var/lib
[safe_mysqld]
err-log = /var/log/mysqld.log
pid-file = /var/run/mysqld/mysqld.pidHere, you can specify a different directory for the error log, otherwise you should not change any entry in this table.
3) Basic Administrative MySQL Command
Here is the list of the important MySQL commands, which you will use time to time to work with MySQL database −
USE Databasename − This will be used to select a database in the MySQL workarea.
SHOW DATABASES − Lists out the databases that are accessible by the MySQL DBMS.
SHOW TABLES − Shows the tables in the database once a database has been selected with the use command.
SHOW COLUMNS FROM tablename: Shows the attributes, types of attributes, key information, whether NULL is permitted, defaults, and other information for a table.
SHOW INDEX FROM tablename − Presents the details of all indexes on the table, including the PRIMARY KEY.
SHOW TABLE STATUS LIKE tablename\G − Reports details of the MySQL DBMS performance and statistics.
4) Important Mysqladmin Commands for Database Administration in Linux
1. How to change the MySQL root user password?
# mysqladmin -u root -ptmppassword password 'newpassword'
# mysql -u root -pnewpassword
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.1.25-rc-community MySQL Community Server (GPL)
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql>2. How to check whether MySQL Server is up and running?
# mysqladmin -u root -p ping
Enter password:
mysqld is alive3. How do I find out what version of MySQL I am running?
Apart from giving the ‘Server version’, this command also displays the current status of the mysql server.
# mysqladmin -u root -ptmppassword version
mysqladmin Ver 8.42 Distrib 5.1.25-rc, for redhat-linux-gnu on i686
Copyright (C) 2000-2006 MySQL AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license
Server version 5.1.25-rc-community
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /var/lib/mysql/mysql.sock
Uptime: 107 days 6 hours 11 min 44 sec
Threads: 1 Questions: 231976 Slow queries: 0 Opens: 17067
Flush tables: 1 Open tables: 64 Queries per second avg: 0.254. What is the current status of MySQL server?
# mysqladmin -u root -ptmppassword status
Uptime: 9267148
Threads: 1 Questions: 231977 Slow queries: 0 Opens: 17067
Flush tables: 1 Open tables: 64 Queries per second avg: 0.25The status command displays the following information:
Uptime: Uptime of the mysql server in seconds
Threads: Total number of clients connected to the server.
Questions: Total number of queries the server has executed since the startup.
Slow queries: Total number of queries whose execution time waas more than long_query_time variable’s value.
Opens: Total number of tables opened by the server.
Flush tables: How many times the tables were flushed.
Open tables: Total number of open tables in the database.
5. How to view all the MySQL Server status variable and it’s current value?
# mysqladmin -u root -ptmppassword extended-status
+-----------------------------------+-----------+
| Variable_name | Value |
+-----------------------------------+-----------+
| Aborted_clients | 579 |
| Aborted_connects | 8 |
| Binlog_cache_disk_use | 0 |
| Binlog_cache_use | 0 |
| Bytes_received | 41387238 |
| Bytes_sent | 308401407 |
| Com_admin_commands | 3524 |
| Com_assign_to_keycache | 0 |
| Com_alter_db | 0 |
| Com_alter_db_upgrade | 0 |6. How to display all MySQL server system variables and the values?
# mysqladmin -u root -ptmppassword variables
+---------------------------------+---------------------------------+
| Variable_name | Value |
+---------------------------------+---------------------------------+
| auto_increment_increment | 1 |
| basedir | / |
| big_tables | OFF |
| binlog_format | MIXED |
| bulk_insert_buffer_size | 8388608 |
| character_set_client | latin1 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
skip.....
| time_format | %H:%i:%s |
| time_zone | SYSTEM |
| timed_mutexes | OFF |
| tmpdir | /tmp |
| tx_isolation | REPEATABLE-READ |
| unique_checks | ON |
| updatable_views_with_limit | YES |
| version | 5.1.25-rc-community |
| version_comment | MySQL Community Server (GPL) |
| version_compile_machine | i686 |
| version_compile_os | redhat-linux-gnu |
| wait_timeout | 28800 |
+---------------------------------+---------------------------------+7. How to display all the running process/queries in the mysql database?
# mysqladmin -u root -ptmppassword processlist
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 20 | root | localhost | | Sleep | 36 | | |
| 23 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+You can use this command effectively to debug any performance issue and identify the query that is causing problems, by running the command automatically every 1 second as shown below.
# mysqladmin -u root -ptmppassword -i 1 processlist
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 20 | root | localhost | | Sleep | 36 | | |
| 23 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 24 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+8. How to create a MySQL Database?
# mysqladmin -u root -ptmppassword create testdb
# mysql -u root -ptmppassword
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 705
Server version: 5.1.25-rc-community MySQL Community Server (GPL)
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| sugarcrm |
| testdb |
+--------------------+
4 rows in set (0.00 sec)Note: To display all tables in a database, total number of columns, row, column types, indexes etc., use the mysqlshow command that we discussed in our previous articles.
9. How to Delete/Drop an existing MySQL database?
# mysqladmin -u root -ptmppassword drop testdb
Dropping the database is potentially a very bad thing to do.
Any data stored in the database will be destroyed.
Do you really want to drop the 'testdb' database [y/N] y
Database "testdb" dropped
# mysql -u root -ptmppassword
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 707
Server version: 5.1.25-rc-community MySQL Community Server (GPL)
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| sugarcrm |
+--------------------+
3 rows in set (0.00 sec)10. How to reload/refresh the privilege or the grants tables?
# mysqladmin -u root -ptmppassword reload;Refresh command will flush all the tables and close/open log files.
# mysqladmin -u root -ptmppassword refresh11. What is the safe method to shutdown the MySQL server?
# mysqladmin -u root -ptmppassword shutdown
# mysql -u root -ptmppassword
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/lib/mysql/mysql.sock'Note: You can also use “/etc/rc.d/init.d/mysqld stop” to shutdown the server. To start the server, execute “/etc/rc.d/init.d/mysql start”
12. List of all mysqladmin flush commands.
# mysqladmin -u root -ptmppassword flush-hosts
# mysqladmin -u root -ptmppassword flush-logs
# mysqladmin -u root -ptmppassword flush-privileges
# mysqladmin -u root -ptmppassword flush-status
# mysqladmin -u root -ptmppassword flush-tables
# mysqladmin -u root -ptmppassword flush-threadsflush-hosts: Flush all information in the host cache.
flush-privileges: Reload the grant tables (same as reload).
flush-status: Clear status variables.
flush-threads: Flush the thread cache.
13. How to kill a hanging MySQL Client Process?
First identify the hanging MySQL client process using the processlist command.
# mysqladmin -u root -ptmppassword processlist
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 20 | root | localhost | | Sleep | 64 | | |
| 24 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+Now, use the kill command and pass the process_id as shown below. To kill multiple process you can pass comma separated process id’s.
# mysqladmin -u root -ptmppassword kill 20
# mysqladmin -u root -ptmppassword processlist
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 26 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+14. How to start and stop MySQL replication on a slave server?
# mysqladmin -u root -ptmppassword stop-slave
Slave stopped
# mysqladmin -u root -ptmppassword start-slave
mysqladmin: Error starting slave: The server is not configured as slave;
fix in config file or with CHANGE MASTER TO15. How to combine multiple mysqladmin commands together?
In the example below, you can combine process-list, status and version command to get all the output together as shown below.
# mysqladmin -u root -ptmppassword process status version
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+----+---------+------+-------+------------------+
| 43 | root | localhost | | Query | 0 | | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+
Uptime: 3135
Threads: 1 Questions: 80 Slow queries: 0 Opens: 15 Flush tables: 3
Open tables: 0 Queries per second avg: 0.25
mysqladmin Ver 8.42 Distrib 5.1.25-rc, for redhat-linux-gnu on i686
Copyright (C) 2000-2006 MySQL AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license
Server version 5.1.25-rc-community
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /var/lib/mysql/mysql.sock
Uptime: 52 min 15 secYou can also use the short form as shown below:
# mysqladmin -u root -ptmppassword pro stat verUse the option -h, to connect to a remote MySQL server and execute the mysqladmin commands as shown below.
# mysqladmin -h 192.168.1.112 -u root -ptmppassword pro stat ver
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