The previous article
covered a basic MariaDB® server setup on CentOS Linux, including setting the root
password, creating a database, and creating a user for the database. Now
let's look at MariaDB in a little more detail to tweak its
configuration and be ready in case something goes wrong.
By default, you'll find MariaDB's configuration file at the following location:
If it's not there you can use
mysqld to look for the configuration
file by running the following command:
/usr/libexec/mysqld --help --verbose
You'll get a lot of text back. The first part describes the options
that you can send to the server when you launch it. The second part is all
of the configuration information that was set when the server was compiled.
Near the start of the output, find a couple lines that look similar to the following lines:
Default options are read from the following files in the given order: /etc/mysql/my.cnf /etc/my.cnf ~/.my.cnf
The server works down the list until it finds a configuration file.
Open the my.cnf file and have a look inside.
Any lines starting with
# are comments, and they mostly document what
the different settings are for. You'll find details like the location of log files and where the database files
There are lines in the config file that just contain a word in square
brackets, like [client] or [mysqld]. Those are config groups
and they tell the programs that read the configuration file which parts
they should pay attention to.
MariaDB is technically a collection of tools that includes the server (mysqld), the client (mysql), and some other tools. Programs look in my.cnf to see how they should behave.
Basically, the mysql configuration section controls the client, and the mysqld section controls the server.
If something goes wrong, the best place to start troubleshooting any
program is its logs. By default MariaDB stores its log files in the
Note: You might need to use
sudo to get a listing of the files in that
If you don't find the logs in the default directory, you need to
check MariaDB's configuration. Look in the my.cnf file and look for a
log_error line, as in:
log_error = /var/log/mariadb/mariadb.log
If you don't see a line like that, create one in the mysqld section so that
MariaDB will use its own error log. We recommend using the location in the
example and creating the /var/log/mariadb directory if it doesn't already
exist. Apply the change by restarting MariaDB with the following command:
systemctl restart mariadb
Make sure that the log directory you choose can be written to by the user
controlling the MariaDB process.
There might be a port setting under both the client and server configuration
sections. The port under the server section controls the port that the
server listens to. By default, it is 3306, but you can change it to
anything you'd like.
The port in the client section tells the client the port to connect to
by default. You generally want the two port settings to match up.
If you don't see the port entries in the configuration file, that means
the ports are using the default. If you want to change the port, add
the lines in the appropriate categories, as shown in the following example:
[client] port = 3306 [mysqld] port = 3306
The other network setting to look for is the bind-address value. It
usually is set to the address for localhost, 127.0.0.1. By binding to
localhost, the server makes sure no one can connect to it from outside of
the local machine.
If you're running your MariaDB server on a different machine from your
application you want to bind to a remotely accessible address instead
of localhost. Change the bind-address setting to match your public IP
address (or, even better, to a backend IP address on a network that fewer
machines can access).
If you don't see a bind-address entry, you should put one into the
mysqld category to help control access to the server, similar to the following example:
[mysqld] bind-address = 127.0.0.1
Remember to account for the client's hostname when you set up your
database users and to configure your firewall if you're running
Behind the scenes there are actually two versions of the MariaDB server,
mysqld and mysqld_safe. Both read the same configuration sections. The
main difference is that mysqld_safe launches with a few safety
features enabled to make it easier to recover from a crash or other
Both mysqld and mysqld_safe will read config entries in the mysqld
section. If you include a mysqld_safe section, then only mysqld_safe
reads those values.
By default the mysql service launches mysqld_safe. You should only change this if you are really sure about what you're doing.
The mysqladmin tool enables you to perform some administrative functions from the command line. This tool is not covered in this article because this article covers the basics to get you up and running.
You can look at this tool in more depth later to see what it can do,
particularly if you need to build scripts that perform functions like
checking the status of the server or creating and dropping databases.
When it comes to making backups of your databases
(apart from the approach to back up the entire machine), you have a few
options. The main options
are copying the database files and using mysqldump.
By default, MariaDB creates a directory for each database in its data
directory that looks similar to the following example:
After you've found the data directory, don't make a copy of it immediately. When the database server is active, it might be writing new
values to tables at any time. If it writes to a table halfway
through your copy, some files will change and lead to a corrupt backup.
If you're trying to plan for disaster recovery, this is not a good thing.
To make sure the database files are copied cleanly, shut the
MariaDB server down entirely before the copy. That's safe but isn't always
Another approach you can take is to lock the database as read-only for
the duration of the copy. Then when you're done, release the lock. This
way your applications can still read data while you're backing up files.
Lock the databases to read-only by running the following command from the command line:
mysql -u root -p -e "FLUSH TABLES WITH READ LOCK;"
To unlock the database when you're done, run this command:
mysql -u root -p -e "UNLOCK TABLES;"
The options -e with the mysql client tells the client to run
the query in quotes as if it were entered in with the mysql shell.
If you're setting these commands up in a script, you can put
the password in quotes right after -p with no space between the two,
as in the following example:
mysql -u root -p"password" -e "FLUSH TABLES WITH READ LOCK;" mysql -u root -p"password" -e "UNLOCK TABLES;"
Note: Make sure that you set the permissions on that file to restrict read
access to protect the password.
Another approach to backing up your database is to use the mysqldump
tool. Rather than copying the database files directly, mysqldump
generates a text file that represents the database. By default, the text
file contains a list of SQL statements that you would use to recreate the
database, but you can also export the database in another format like
CSV or XML. You can read the mysqldump man page to see all its
The statements generated by mysqldump go to standard output.
You want to specify a file to redirect the output to when you run it.
mysqldump -u root -p demodb > dbbackup.sql
That command tells mysqldump to recreate the demodb database in
SQL statements and to write them to the file dbbackup.sql. Note that
the username and password options function the same as the mysql client,
so you can include the password directly after -p in a script.
Restoring a database copied with mysqldump looks similar to what was used to create it, but you use mysql instead of mysqldump, as shown
in the following command:
mysql -u root -p demodb < dbbackup.sql
You also change from using a greater-than to a less-than sign, which switches
the command from redirecting its output to telling it to read its input
from the existing file. The input is sent to the mysql command
and causes the instructions in the copy made with mysqldump to recreate the database.
By default, the SQL statements that are generated add to
existing database tables without overwriting them. If you're restoring a
backup over an existing database, you should drop the database's tables
first, or drop and recreate the database itself. You can change that
behavior by using the --add-drop-table option with the command that
creates the mysqldump. Doing so causes mysqldump to add a command to the
backup files that it writes that drops tables before recreating them.
The last concept to cover in this article is the database engine.
The engine is the process that's churning away behind the scenes,
writing to and reading from files. You won't usually need to know
anything other than that it's there, but sometimes you want to run an
application that's been optimized for a particular database engine.
The engine type is set when a table is created. Tables are usually
created by the application that's going to use them.
To see the engine used by your database's tables, you can run the
following command in the MariaDB shell, changing demodb to the name
of your database:
SHOW TABLE STATUS FROM demodb;
Ideally you won't need to choose an engine. If you're not very familiar
with MariaDB, that's the safest way to go. Let the application
handle this, and if you're writing the application, use the default
engine until you're more comfortable with your options.
The database engines used most often with MariaDB are MyISAM and
Because MyISAM has been the default in MySQL for a while, it's the most
compatible with MariaDB. Certain types of searches
perform better on MyISAM than InnoDB. Just because it's the older of the
two doesn't mean that it can't be the best for a given application type.
InnoDB is more fault-tolerant than MyISAM and handles crashes and
recovery with a much smaller chance of database corruption. This is a
However, for best performance, InnoDB requires a lot of tweaking for your environment and access patterns. If you have a
DBA, this work might not be a problem. But if you're a developer who wants a
database up and running for a test server, you probably won't want to
deal with tuning InnoDB.
At this point, you should have a good understanding of MariaDB. For more information, see the MariaDB documentation site.
Updated 18 days ago