Hmm, nice little error when trying to start db2 on solaris 10, stating that it was unable to start up the database and i should check my SHM settings!
prctl reported correct project settings, so tried truss:-
# truss -f db2start truss: cannot trace set-id or unreadable object file: db2start
Cue alarm bells, proven by trusty "ls":
# truss -f db2start -rwsr-xr-x 1 root root 238584 Jul 10 12:28 db2start
Add root to the user.db2inst1 project with a quick projmod -a -U root user.db2inst1 and try again.