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>"