1.0 Introduction

1.1 About this manual

This manual is an introduction to Legion 1.6.x. It gives instructions for logging in to an active Legion system and a high-level introduction to Legion context space. Users who need to install or start a Legion system should consult the System Administrator Manual. If you need more help please contact us (legion-help@virginia.edu).

There are three additional Legion manuals. The System Administrator Manual has information for Legion system administrators, including installing and running a Legion system, configuring security features, and managing resources. The Developer Manual provides information and documentation for Legion programmers and includes information about languages, libraries, core objects, and implementing new objects. The Reference Manual is a more specialized resource, providing detailed information about specific elements of the Legion system. There are also man pages for all Legion commands, included with the system files, and several on-line tutorials on the Legion web site (http://legion.virginia.edu).

This manual assumes that you are working on a previously installed, compiled, and running system.1 Before going any further, be sure that the system is properly installed and running. Check with your system administrator if you are unsure.

1.2 Style conventions

The manuals at times refer to path names in Unix directory space and in Legion context space. To avoid confusion, the following style conventions are used:

  • Unix, DOS, and local path names appear in normal font
  • Context path names appear in fixed font
  • GUI commands appear in grey helvetica

Functions, method names, parameters, flags, and command-line utilities (such as rm, cp, and legion_ls) also appear in fixed font.

1.3 About Legion

Developed at the University of Virginia, Legion is an integrated software system for distributed parallel computation. While fully supporting existing codes written in MPI and PVM, Legion provides features and services that allow users to take advantage of much larger, more complex resource pools. With Legion, for example, a user can easily run a computation on a supercomputer at a national center while dynamically visualizing the results on a local machine or schedule and run a large parameter space study on several workstation farms simultaneously. Legion permits computational scientists to use cycles wherever they are, allowing bigger jobs to run in shorter times through higher degrees of parallelization.

Key capabilities include the following:

  • Legion eliminates the need to move and install binaries manually on multiple platforms. After Legion schedules a set of tasks over multiple remote machines, it automatically transfers the appropriate binaries to each host. A single job can run on multiple heterogeneous architectures simultaneously; Legion will ensure that the right binaries go to each, and that it only schedules onto architectures for which it has binaries.
  • Legion provides a virtual file system that spans all the machines in a Legion system. Input and output files can be seen by all the parts of a computation, even when the computation is split over multiple machines that don't share a common file system. Different users can also use the virtual file system to collaborate, sharing data files and even accessing the same running computations.
  • Legion's object-based architecture dramatically simplifies building add-on tools for tasks such as visualization, application steering, load monitoring, and job migration.
  • Legion provides optional privacy and integrity of communications for applications distributed over public networks. Multiple users in a Legion system are protected from one another.

These features also make Legion attractive to administrators looking for ways to increase and simplify the use of shared high-performance machines. The Legion implementation emphasizes extensibility, and multiple policies for resource use can be embedded in a single Legion system that spans multiple resources or even administrative domains.


1. It is actually not always necessary to have a Legion system running in order to use Legion: some Legion hosts can run as client hosts in a larger Legion system. A client host does not have the full set of Legion system binaries, but a set of binary executable files that can contact other Legion hosts in its Legion system. For more information on this option, please e-mail us at legion-help@virginia.edu. Back

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