DUMPDIR configuration parameter

DUMPDIR specifies a directory in which the database server dumps shared memory, gcore files, or messages from a failed assertion.

Because shared memory can be large, set DUMPDIR to a file system with a significant amount of space. The directory to which DUMPDIR is set must exist for the server to start.
onconfig.std values
On UNIX: $INFORMIXDIR/tmp

On Windows: $INFORMIXDIR\tmp

values
Any directory to which user informix has write access
takes effect
After you edit your onconfig file and restart the database server.