esegui locate initdb dovrebbe darti la lista da scegliere. come:
MacBook-Air:~ vao$ locate initdb
/usr/local/Cellar/postgresql/9.5.3/bin/initdb
/usr/local/Cellar/postgresql/9.5.3/share/doc/postgresql/html/app-initdb.html
/usr/local/Cellar/postgresql/9.5.3/share/man/man1/initdb.1
/usr/local/Cellar/postgresql/9.6.1/bin/initdb
/usr/local/Cellar/postgresql/9.6.1/share/doc/postgresql/html/app-initdb.html
/usr/local/Cellar/postgresql/9.6.1/share/man/man1/initdb.1
/usr/local/bin/initdb
/usr/local/share/man/man1/initdb.1
Quindi nel mio caso voglio correre
/usr/local/Cellar/postgresql/9.6.1/bin/initdb
Se non hai installato mlocate, installalo o usa
sudo find / -name initdb
