openstack-manuals/doc/user-guide/source/cli_provide_user_data_to_instances.rst

Provide user data to instances

A user data file is a special key in the metadata service that holds a file that cloud-aware applications in the guest instance can access. For example, one application that uses user data is the cloud-init system, which is an open-source package from Ubuntu that is available on various Linux distributions and which handles early initialization of a cloud instance.

You can place user data in a local file and pass it through the --user-data <user-data-file> parameter at instance creation:

$ nova boot --image ubuntu-cloudimage --flavor 1 --user-data mydata.file