User Management
From Briki
To add a new user, run:
sudo adduser userid
To add a system user suitable for running daemon processes, run:
sudo adduser --system --no-create-home --group userid
See man adduser for more options. NB. Maximum username length is 8 chars - although this script won't enforce it, it will stop many processes/tools from displaying the username properly.
To add a user to an existing group:
sudo adduser user group
To add a picture for a user (which will be displayed in the login screen, select System->Preferences->About Me