su
AccountsPackage: util-linux
Opens a shell as another identity, asking for that account's password — not yours. On a server where root has no password, su fails and sudo -i is the intended route.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
su -c- Hands one command to the target's shell instead of opening an interactive session:
su - postgres -c psqlruns psql, then returns. su --login- The long form of the dash in
su -: a full login session — environment cleared except TERM, PATH rebuilt, profiles read, starting in the target's home directory.