mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0,00 sec)

magento setup:install --base-url=http://127.0.0.1/magento2/
--db-host=localhost --db-name=magento --db-user=magento --db-password=magento
--admin-firstname=Magento --admin-lastname=User --admin-email=user@example.com
--admin-user=admin --admin-password=admin123 --language=en_US
--currency=USD --timezone=America/Chicago --use-rewrites=1

root@vegan:/var/www/html/magento2/bin# ./magento setup:install --base-url=http://127.0.0.1/magento2/ --db-host=localhost --db-name=magento --db-user=magento --db-password=magento --admin-firstname=Magento --admin-lastname=User --admin-email=user@example.com --admin-user=admin --admin-password=admin123 --language=en_US --currency=USD --timezone=America/Chicago --use-rewrites=1
SQLSTATE[HY000] [1045] Access denied for user 'magento'@'localhost' (using password: YES)



  [InvalidArgumentException]
  Parameter validation failed

setup:install [--backend-frontname="..."] [--key="..."] [--session-save="..."] [--definition-format="..."] [--db-host="..."]

--db-user

User name of the Magento database instance owner.

Default is root.

root@vegan:/var/www/html/magento2/bin# ./magento setup:install --base-url=http://127.0.0.1/magento/ --db-host=localhost --db-name=magentodb --db-user=root --db-password= root --admin-user=admin --admin-password=admin123 --language=en_US --currency=USD --timezone=America/Chicago --cleanup-database help



  [RuntimeException]
  Too many arguments.

root@vegan:/var/www/html/magento2/bin# ./magento setup:install --base-url=http://127.0.0.1/magento/ --db-host=localhost --db-name=magentodb --db-user=root --db-password= root



  [RuntimeException]
  Too many arguments.

/var/www/html/magento2/bin

root@vegan:/var/www/html/magento2/bin# ./magento setup:install admin-user="root"



  [RuntimeException]
  Too many arguments.