Create users and groups in Linux

# create linux group
groupadd groupname

# add user to group (primary)
useradd -g groupname kyfoo

# add user to group (secondary)
useradd -G groupname kyfoo

# modify user group (primary)
usermod -g groupname kyfoo

# modify user group (secondary)
usermod -G groupname kyfoo

# add password to user account
passwd kyfoo