user admin
add new user
useradd -m -G sudo -p <password> <username>
add new service account
sudo useradd --system --no-create-home ampache
add new user with custom home dir
sudo useradd -m -d /opt/username username
add user to group
sudo usermod -a -G media pi
make a new group with gid
sudo groupadd -g 1010 media
run as another user that has /bin/nologin set
su -m <user> -c "<command>"