d-i manual: 3 "jessie" remain in current guide
these should be updated as this is for stretch :)
Under the SysV init system <command>halt</command> had the same
effect as <command>poweroff</command>, but with systemd as init
system (the default in jessie) their effects are different.
the default since jessie
the default in stretch
no idea if these are still valid also for stretch;
The graphical installer is not enabled on the arm64 &d-i; images
for jessie so the serial console is used.
... Also USB is not supported in the jessie kernel so
installing from a USB stick does not work. ...
no need to CC me :-)