Debian and Ubuntu

1RUN set -eu;\
2    useradd --user-group --create-home --comment="$comment" "$username";\
3    yes "$password" | passwd "$username"

Alpine

1RUN yes "$password" | adduser --gecos "$comment" "$username"

Variables

• $username — username;
• $password — password (can be equal to username for convenience);
• $comment — comment (GECOS field).

Documentation

• useradd(8) — Debian Bullseye
• useradd(8) — Ubutnu 20.04 LTS (Focal Fossa)
• useradd(8) — Ubutnu 22.04 LTS (Jammy Jellyfish)
• Setting up a new user — Alpine Linux