RHEL 6 Managing Confined Services - 10.4. Configuration Examples

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10.4. Configuration Examples

10.4.1. MySQL Changing Database Location

When using Red Hat Enterprise Linux 6, the default location for MySQL to store its database is /var/lib/mysql. This is where SELinux expects it to be by default, and hence this area is already labeled appropriately for you, using the mysqld_db_t type.

The location where the database is stored can be changed depending on individual environment requirements or preferences, however it is important that SELinux is aware of this new location - that it is labeled accordingly. This example explains how to change the location of a MySQL database and then how to label the new location so that SELinux can still provide its protection mechanisms to the new area based on its contents.

Note that this is an example only and demonstrates how SELinux can affect MySQL. Comprehensive documentation of MySQL is beyond the scope of this document. Refer to the official MySQL documentation for further details. This example assumes that the mysql-server and setroubleshoot-server packages are installed, that the auditd service is running, and that there is a valid database in the default location of /var/lib/mysql.

Run ls -lZ /var/lib/mysql to view the SELinux context of the default database location for mysql:
```
# ls -lZ /var/lib/mysql
drwx------. mysql mysql unconfined_u:object_r:mysqld_db_t:s0 mysql
```
This shows mysqld_db_t which is the default context element for the location of database files. This context will have to be manually applied to the new database location that will be used in this example in order for it to function properly.

Enter mysqlshow -u root -p and enter the mysqld root password to show the available databases:

# mysqlshow -u root -p
Enter password: *******
+--------------------+
|     Databases      |
+--------------------+
| information_schema |
| mysql              |
| test               |
| wikidb             |
+--------------------+

Shut down the mysqld daemon with service mysqld stop as the root user:

# service mysqld stop
Stopping MySQL:                                            [  OK  ]

Create a new directory for the new location of the database(s). In this example, /opt/mysql is used:
```
# mkdir -p /opt/mysql
```
Copy the database files from the old location to the new location:
```
# cp -R /var/lib/mysql/* /opt/mysql/
```
Change the ownership of this location to allow access by the mysql user and group. This sets the traditional Unix permissions which SELinux will still observe.
```
# chown -R mysql:mysql /opt/mysql
```
Run ls -lZ /opt to see the initial context of the new directory:
```
# ls -lZ /opt
drwxr-xr-x. mysql mysql unconfined_u:object_r:usr_t:s0   mysql
```
The context usr_t of this newly created directory is not currently suitable to SELinux as a location for MySQL database files. Once the context has been changed, MySQL will be able to function properly in this area.
Open the main MySQL configuration file /etc/my.cnf with a text editor and modify the datadir option so that it refers to the new location. In this example the value that should be entered is /opt/mysql.
```
[mysqld]
datadir=/opt/mysql
```
Save this file and exit.
Run service mysqld start as the root user to start mysqld. The service should fail to start, and a denial will be logged to /var/log/messages:
```
SELinux is preventing /usr/libexec/mysqld "write" access on /opt/mysql. For complete SELinux messages. run sealert -l b3f01aff-7fa6-4ebe-ad46-abaef6f8ad71
```
The reason for this denial is that /opt/mysql is not labeled correctly for MySQL data files. SELinux is stopping MySQL from having access to the content labeled as usr_t. Perform the following steps to resolve this problem:
Run the semanage command to add a context mapping for /opt/mysql:
```
semanage fcontext -a -t mysqld_db_t "/opt/mysql(/.*)?"
```

This mapping is written to the /etc/selinux/targeted/contexts/files/file_contexts.local file:

# grep -i mysql /etc/selinux/targeted/contexts/files/file_contexts.local

/opt/mysql(/.*)?    system_u:object_r:mysqld_db_t:s0

Now use the restorecon command to apply this context mapping to the running system:
```
restorecon -R -v /opt/mysql
```
Now that the /opt/mysql location has been labeled with the correct context for MySQL, the mysqld daemon starts:
```
# service mysqld start
Starting MySQL:                                            [  OK  ]
```

Confirm the context has changed for /opt/mysql:

ls -lZ /opt
drwxr-xr-x. mysql mysql system_u:object_r:mysqld_db_t:s0 mysql

The location has been changed and labeled, and the mysqld daemon has started successfully. At this point all running services should be tested to confirm normal operation.