useradd
AccountsPackage: passwd
Creates an account with exactly what you specify and nothing more: without -m no home directory, without -s the shell is /bin/sh. It is the low-level tool scripts call; for a person, adduser asks the right questions.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
useradd --system- Creates a system account: the identifier comes from the
SYS_UID_MIN–SYS_UID_MAXrange in/etc/login.defs,/etc/shadowgets no aging information, and no home directory is created — regardless ofCREATE_HOME.
Lessons that teach it
No lesson names it among its useful commands; it appears inside other lessons' command lines.