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.
When you reset the value dynamically in your onconfig file by running the onmode -wf command.
When you reset the value in memory by running the onmode -wm command.