Glossary of Terms
=================

.. glossary::
   :sorted:

   Channel

     Channels are the key component of the ZeroVM I/O subsystem. On
     the host system side, channels are backed by the file system
     using regular files, pipes, character devices, or TCP sockets. On
     the guest side, each channel is a device file, which can either
     be used as a character or block device.

     Channels are the only way for ZeroVM to communicate with the
     "outside world", i.e., the host file system, other ZeroVM nodes,
     etc. Before a ZeroVM instance starts, channels must be declared
     in the :term:`manifest`.

   Daemon mode

     ZeroVM can be started in daemon mode to reduce startup of
     instances/nodes in a multi-node job. Although ZeroVM startup time
     is ~5ms, user programs, for example, running on :term:`zpython`,
     will incur an additional startup penalty. Daemon mode allows a
     multi-node computation to "pre-warm" an instance and fork
     additional copies for each unit of computation, thereby paying
     the additional startup time penalty only once.

   Manifest

     A text file which must be provided to ZeroVM in order to run a
     :term:`NaCL` application. Manifest files must include the
     following *mandatory* fields:

     - ``Version``: Manifest format version.
     - ``Program``: Full path to a :term:`NaCL` application to be
       validated and run.
     - ``Timeout``: Timeout, in seconds. ZeroVM will stop the user
       program and exit after the specified time has elapsed. Valid
       values are 1..2147483647.
     - ``Memory``: Memory space in bytes available for the user
       program.
     - ``Channel``: Mapping for I/O between a ZeroVM instance and the
       host system. Multiple channels be specified in a manifest.

     Manifests can also contain the following *optional* fields:

     - ``Nameserver``: Address of a nameserver which resolves network
       channel definitions.
     - ``Node``: Node ID number of a given ZeroVM instance in a
       cluster of VMs. Manditory if ``NameServer`` is specified.
     - ``Job``: Path to a Unix socket. Used for receiving
       commands/manifests and to send reports in :term:`daemon mode`.

   .. TODO(larsbutler): Add a more detailed `manifest` page and link
   .. it here. It would be nice to basically link to a detailed page
   .. containing all of this:
   .. https://github.com/zerovm/zerovm/blob/master/doc/manifest.txt

   Native Client
   NaCl

     See http://en.wikipedia.org/wiki/Google_Native_Client.

   NVRAM (configuration file)

     `INI-style <http://en.wikipedia.org/wiki/INI_file>`_
     configuration file used by ZeroVM and the :term:`ZRT`. Includes
     the following:

     - ``[fstab]`` section: Channel definitions for ``tar`` images to
       be mounted as directory/file hierarchies in the in-memory file
       system.
     - ``[env]`` section: Environment variable definitions.
     - ``[mapping]`` section: Channel definitions for stdin, stdout,
       stderr, and other devices not included in ``[fstab]``.
     - ``[debug]`` section: Optional. Debug verbosity level
       configuration.
     - ``[time]`` section: Optional. Defines the starting time for the
       ZeroVM clock. With this you can define the number of seconds
       since Jan 1, 1970. (See `Unix time
       <http://en.wikipedia.org/wiki/Unix_time>`_.)

   .. TODO(larsbutler): Linked more detailed docs page here, with a
   .. full description of the NVRAM file and all of its fields.

   System Map

     The system map is the JSON configuration file that is passed to
     the ZeroCloud middleware when executing a job within ZeroCloud.
   
   Trusted

     ZeroVM and the :term:`ZRT`. Provides a secure sandbox for running
     :term:`untrusted` code.

   Untrusted

     User code run inside the ZeroVM :term:`NaCL`-based sandbox.
     Untrusted code is `validated
     <https://github.com/zerovm/validator>`_ before it is run.

   .. TODO(larsbutler): This description needs expansion/improvement.

   ZeroVM Application
   zapp

     An archive file (typically created by :term:`zpm`) containing a
     ``zapp.yml`` configuration file and user application code.

   ZeroCloud

     Middleware for `OpenStack Swift
     <https://wiki.openstack.org/wiki/Swift>`_ which provides the
     capability to run ZeroVM applications on object storage nodes.
     Can be used to initiate map/reduce-style jobs on collections of
     Swift objects.

     See https://github.com/zerovm/zerocloud.

   Zebra

     Custom-configured deployment of :term:`ZeroCloud`, hosted by
     `Rackspace <https://rackspace.com>`_. :term:`Zebra` is an
     alpha-testing service and playground for :term:`ZeroCloud`.

   ZeroVM Package Manager
   zpm

     Command-line utility which helps to create, bundle, deploy (to
     :term:`ZeroCloud`), and execute (on :term:`ZeroCloud`) ZeroVM
     user applications.

     See https://github.com/zerovm/zpm.

   zpython

     ZeroVM ports of CPython interpreters. There are ongoing efforts
     to port both `Python 2.7.3 <https://github.com/zerovm/zpython2>`_
     and `Python 3.2.2 <https://github.com/zerovm/zpython>`_ to run
     inside ZeroVM.

   ZeroVM Runtime
   ZRT

     Provides a POSIX-like environment and in-memory file system for
     use by :term:`untrusted` user programs.

   ZeroVM Shell
   zvsh

     Utility program which makes ZeroVM easy to use by providing rich
     command-line options for running and debugging ZeroVM instances.
     Also includes manifest/NVRAM configuration file generation
     functionality (so you don't have to write all of your
     configuration files by hand).

     See https://github.com/zerovm/zerovm-cli.

   Zwift

     Deprecated synonym for :term:`ZeroCloud`.