The sbuild man page mentions a default chroot-mode in a few places: * In the description of the --chroot-mode argument: "Select the desired chroot mode. Four values are possible: schroot (the default)", [...] * In the CHROOT MODES section's introductory paragraph: "The default backend (or chroot mode) is schroot which is an suid binary that allows regular users to enter a chroot environment." * In the CHROOT MODES section's description of unshare: "The default and recommended chroot mode." Given the other context available, I believe that unshare is indeed the default, and the other instances should be changed to match.