add user to group

# official, cross distribution (tested with suse12, centos7, debian8)
usermod -a -G GROUPNAME USERNAME

# redhat/centos:
usermod -a -G wheel user; # add user „user“ to group „wheel“ in order to allow user to use sudo

# debian:
usermod -a -G sudo user; # allows user bob to run processes with root-privileges temporarily

# debian8 only
adduser username group; # add username to the group
adduser user lpadmin; # adds the user "user" to the group "lpadmin" (if cups installed allows the user to add/delete printers)

User will have to re-login to active changes!

admin