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MySQL 5.4 Reference Manual :: 7 Optimization :: 7.6 Disk Issues :: 7.6.1 Using Symbolic Links :: 7.6.1.1 Using Symbolic Links for Databases on Unix
7.6.1.2 Using Symbolic Links for Tables on Unix »
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7.6.1.1. Using Symbolic Links for Databases on Unix

On Unix, the way to symlink a database is first to create a directory on some disk where you have free space and then to create a symlink to it from the MySQL data directory. 

shell> mkdir /dr1/databases/test
shell> ln -s /dr1/databases/test /path/to/datadir

MySQL does not support linking one directory to multiple databases. Replacing a database directory with a symbolic link works as long as you do not make a symbolic link between databases. Suppose that you have a database db1 under the MySQL data directory, and then make a symlink db2 that points to db1: 

shell> cd /path/to/datadir
shell> ln -s db1 db2

The result is that, or any table tbl_a in db1, there also appears to be a table tbl_a in db2. If one client updates db1.tbl_a and another client updates db2.tbl_a, problems are likely to occur.

However, if you really need to do this, it is possible by altering the source file mysys/my_symlink.c, in which you should look for the following statement: 

if (!(MyFlags & MY_RESOLVE_LINK) ||
    (!lstat(filename,&stat_buff) && S_ISLNK(stat_buff.st_mode)))

Change the statement to this: 

if (1)

User Comments

Posted by [name withheld] on March 4 2003 5:25am[Delete] [Edit]

When writing symbolic link files from VB, don't use the Open for Input/Write statements, as that puts quotation marks around the path string, which MySQL rejects. The Open for Binary/Put statements do work.

Posted by [name withheld] on March 4 2003 5:34am[Delete] [Edit]

A clarification, which should be obvious: Open for Output/Write doesn't work for symbolic links. I said Open for Input. It's early.

Posted by Paul Mothersdill on September 8 2003 12:21am[Delete] [Edit]

Just in case anybody else is stupid enough to try reading the above late at night:

Create the directory and symlink (with appropriate permissions) _before_ doing anything in MySQL. All "create database" does is to create the directory -- creating the directory and symlink outside MySQL are the equivalent of a "create database" SQL command.

Posted by Nilesh G on January 26 2008 4:29pm[Delete] [Edit]

If you want quotas for users, setup system quotas for the group in which the user is, then create a separate databases directory in his home directory with permission mysql:usergroup and permission 0755

Then move the databases to that directory and create symbolic links to the original mysql datadir.

Posted by Marcus Bointon on September 8 2008 7:30pm[Delete] [Edit]

If you're symlinking to databases outside /var/lib/mysql and you're getting unexpected "(errno: 13)" (permission denied) errors, check your MySQL settings for AppArmor (particularly on Ubuntu as of 8.04) or SELinux. Specifically, make sure your new path is listed in /etc/apparmor.d/usr.sbin.mysqld then restart apparmor.

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