The data directory does not exist, and
the web server does not have permission to create it.
Please create a data directory inside
the shimmie folder, and make sure the web server has
permission to write to it.
The 'magick' command (from the imagemagick package) could not be found - PHP-GD can be used instead, but the size of thumbnails will be limited.
Please make sure the database you have chosen exists and is empty.
The username provided must have access to create tables within the database.
SQLite with default settings is fine for tens of users with thousands of images. For thousands of users or millions of images, postgres is recommended.
Drivers can generally be downloaded with your OS package manager; for Debian / Ubuntu you want php-pgsql, php-mysql, or php-sqlite3.