A SHELL backend command may produce debugging statements which may be logged but otherwise ignored by slapd. Any output line beginning with the characters ``DEBUG:'' will be treated as a debugging statement by slapd.
This feature can be useful when trying to debug a problem with your SHELL backend. If you turn on SHELL debugging in slapd (level 1024), it will log anything it reads from a SHELL backend, allowing you to see your backend's debugging statements easily.