If you get an error of the following type for some queries, it means that MySQL cannot create a temporary file for the result set in the temporary directory:

Can't create/write to file '\\sqla3fe_0.ism'.

The preceding error is a typical message for Windows; the Unix message is similar.

One fix is to start mysqld with the --tmpdir option or to add the option to the [mysqld] section of your option file. For example, to specify a directory of C:\temp, use these lines:

[mysqld]
tmpdir=C:/temp

The C:\temp directory must exist and have sufficient space for the MySQL server to write to. See Section 4.2.3.3, “Using Option Files”.

Another cause of this error can be permissions issues. Make sure that the MySQL server can write to the tmpdir directory.

Check also the error code that you get with perror. One reason the server cannot write to a table is that the file system is full:

shell> perror 28
OS error code  28:  No space left on device

If you get an error of the following type during startup, it indicates that the file system or directory used for storing data files is write protected. Providing the write error is to a test file, This error is not serious and can be safely ignored.

Can't create test file /usr/local/mysql/data/master.lower-test