# useradd -G developers vivek
useradd -G limit tes
useradd -G limit -s /bin/false tes


Add a existing user to existing group

# usermod -G limit tes

change tony user's primary group to www, enter:
# usermod -g www tony

Add a new user to primary group
# useradd -g developers tony

Removing user from group
#gpasswd -d user groupsname