Dodge:
First, tbstat is obsolete after version 5.x of Informix Online.
Next, check that the INFORMIXDIR shell variable is set to the informix home directory.
Also, check that $INFORMIXDIR/bin exists in the PATH variable.
Last, onstat should exist in $INFORMIXDIR/bin with this ownership and permissions:
-rwxr-sr-x 1 informix informix 3551232 Sep 29 2002 /usr/informix/bin/onstat
Regards,
Ed