на ubuntu 18.04 предлагают использовать sudo bash nextcloud_install_production.sh
я успешно установил nextcloud , но остался вопрос , где же логин и пароль администратора?
Afaik the nextcloud_install_production.sh script calls the adduser.sh script which installs everything under the current user, except you’ve used “ncadmin” as a user. See line 15ff in that script.
You can try to use the occ command line tool (./occ user:list) to check if a user has been created and the same tool can be used to set a new password (./occ user:resetpassword).