Run Zope in background. Used for ZEO (Zope Enterprise Objects)
From http://cvs.zope.org/ZODB3/Doc/zdctl.txt :
If you are playing along on your computer, you cannot have missed that some log output has been spewing to your terminal window. While this may give you a warm and fuzzy feeling that something is actually happening, after a whiile it can get quite annoying (especially if clients are actually connecting to the server). This can be avoided by using the -d flag, which enables "daemon mode":
$ zdctl.py -d -p "runzeo.py -a 9999 -f Data.fs" start
Daemon mode does several subtle things; see for example section 13.3 of "Advanced Programming in the UNIX Environment" by Richard Stevens for a good explanation of daemon mode. For now, the most important effect is that the standard input, output and error streams are redirected to /dev/null, and that the process is "detached" from your controlling tty, which implies that it won't receive a SIGHUP signal when you log out.