User Data is a special key in the metadata service which holds a file that cloud aware applications within the guest instance can access. For example the cloudinit system is an open source package from Ubuntu that handles early initialization of a cloud instance that makes use of this user data. This user-data can be put in a file on your local system and then passed in at instance creation with the flag --user-data <user-data-file> for example: $ nova boot --image ubuntu-cloudimage --flavor 1 --user-data mydata.file