Magento 2 requires specific permissions on the files and folders within its structure, along with correct ownership properties, to function properly. The owner of the file/folder system should have full control properties on all files and folders, meaning read/write/execute.
Along with those properties, the specific permissions needed can be set using the following commands in the root directory of the Magento 2 installation:
find . -type f -exec chmod 644 {} \;
find . -type d -exec chmod 755 {} \;
chmod u+x bin/magento