Debian: create a new user without home directory

How do I create a new user in Debian without home directory?

Not really sure if you can create a user which doesn't have a home directory specified. That being said, the specified home directory doesn't have to exists. You can call the adduser with the option --no-create-home.

adduser --no-create-home foo

(adduser is usually the preferred higher level tool if called interactively.)

According to the man page of useradd(8) you either want to add the parameter -M to your useradd call or you want to set CREATE_HOME=no in /etc/default/useradd.

-M
Do no create the user's home directory,
even if the system wide setting from
/etc/login.defs (CREATE_HOME) is set to yes.

On Debian based systems typically the adduser command is used to create new accounts instead of directly calling useradd.

The adduser option to skip creating a home directory is --no-create-home.