mySQL Error 28

[Amar Shah]

We have a really old app that is running mySQL 3.2 on a linux box.
The app is the the process of getting replaced over the next 3 months.

All of a sudden we started getting these errors with any sql query running with DISTINCT:

select distinct category_name, category_desc, trt_category.category_id from trt_category, bsjoin, trt_article
WHERE trt_article.category_id = trt_category.category_id
AND trt_article.story_id = bsjoin.story_id
AND trt_article.category_id != '1' AND trt_category.category_name != 'Upcoming Meeting'
AND bsjoin.board_id = ".$_GET['board_id']

If I remove the word DISTINCT the query seems to run fine (not with the results I want).
We tried rebooting the server and clearing the tmp folder and that resolved the issue for a day, but it happened again.
We have enough drive space.

[Err] 1 - Can't create/write to file '/tmp/#sql46f_13b_5.MYI' (Errcode: 28)

Any ideas on what can be going on?

------------
from the log file:
Cannot initialize InnoDB as 'innodb_data_file_path' is not set.
If you do not want to use transactional InnoDB tables, add a line
skip-innodb
to the [mysqld] section of init parameters in your my.cnf
or my.ini. If you want to use InnoDB tables, add to the [mysqld]
section, for example,
innodb_data_file_path = ibdata1:10M:autoextend
But to get good performance you should adjust for your hardware
the InnoDB startup options listed in section 2 at
301 Moved Permanently
/usr/libexec/mysqld: ready for connections
160224 13:04:27 /usr/libexec/mysqld: Normal shutdown

-------
this is my disk space:
[root@systemdb root]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 16G 12G 3.3G 78% /
/dev/sda1 99M 9.2M 85M 10% /boot
none 251M 0 251M 0% /dev/shm