Should you wish to prevent systemd being installed when updating from Debian Wheezy to Jessie create a file like /etc/apt/preferences.d/local-pin-init
containing:
Package: systemd-sysv
Pin: release o=Debian
Pin-Priority: -1
and ensure you uninstall the Gnome desktop and choose another as that has a "requires" dependency on systemd. Do this before changing the wheezy entries in your /etc/apt/sources.list
or the more modern /etc/apt/sources.list.d/*.list
components form to the jessie ones.
That is astounding! :astonished: