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how to add new group to user linux

usermod -a -G groupname username

add user to group linux

sudo usermod -aG <groups> <username>

command to add a user to a group

sudo usermod -a -G GROUP USER

linux add user to group

sudo groupadd $GROUP 
sudo usermod -aG $GROUP $USER

create new users and add them in group in linux

useradd -mg [groups] [username]