The Distributed Computing Environment (DCE) is a software system developed in the early 1990s by a consortium that included Apollo Computer (later part of Hewlett-Packard), IBM, Digital Equipment Corporation, and others. The DCE supplies a framework and toolkit for developing client/server applications. The framework includes a remote procedure call (RPC) mechanism known as DCE/RPC, a naming (directory) service, a time service, an authentication service (based on Kerberos), an authorization service and a distributed file system (DFS) known as DCE/DFS. DCE/RPC was derived from an earlier RPC system called the Network Computing System (NCS) created at Apollo Computer. The naming service was derived from work done at DEC. DCE DFS was based on the Andrew file system (AFS), originally developed at Carnegie Mellon University, and later extended by Transarc Corporation (which was later merged into IBM). DCE 1.2.2 was released on 12 January 2005 under a free software license (the LGPL) by The Open Group. DCE 1.1 was available much earlier under the OSF BSD license, and resulted in FreeDCE [1] being available since 2000. FreeDCE contains an implementation of DCOM. Apollo Computer, Inc. ... The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... International Business Machines Corporation (IBM, or colloquially, Big Blue) NYSE: IBM (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, NY, USA. The company manufactures and sells computer hardware, software, infrastructure services and consulting services. ... Digital Equipment Corporation was a pioneering company in the American computer industry. ... Client/Server is a network application architecture which separates the client (usually the graphical user interface) from the server. ... A remote procedure call (RPC) is a protocol that allows a computer program running on one computer to cause a subroutine on another computer to be executed without the programmer explicitly coding the details for this interaction. ... DCE/RPC stands for Distributed Computing Environment / Remote Procedure Calls. DCE/RPC was commissioned by The Open Group, aka the Open Software Foundation in a Request for Technology. One of the key companies that contributed was Apollo, who brought in NCA - Network Computing Architecture which became Network Computing System (NCS... Authentication is the act of establishing or confirming something or someone as authentic. ... A Distributed File System (DFS) is a File System, that supports sharing of files and resources in the form of persistent storage over a network. ... The DCE Distributed File System (DCE/DFS) is the remote file access protocol used with the Distributed Computing Environment. ... DCE/RPC stands for Distributed Computing Environment / Remote Procedure Calls. DCE/RPC was commissioned by The Open Group, aka the Open Software Foundation in a Request for Technology. One of the key companies that contributed was Apollo, who brought in NCA - Network Computing Architecture which became Network Computing System (NCS... Network computing system. ... The Andrew file system (AFS) is a distributed networked file system developed by Carnegie Mellon University as part of the Andrew Project. ... Carnegie Mellon University Carnegie Mellon University is a private research university located in Pittsburgh, Pennsylvania. ... January 12 is the 12th day of the year in the Gregorian calendar. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... Generally speaking, free software license is a phrase used by the free software movement to mean any software license that meets the free software definition of the Free Software Foundation (FSF). ... GNU logo The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved free software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. ... The Open Group is a vendor- and technology- neutral industry consortium with a vision of Boundaryless Information Flow that will enable access to integrated information within and between enterprises based on open standards and global interoperability. ...

To understand why DCE is useful, one must look at its closest competitor - Kerberos. Like DCE, Kerberos is a distributed computing application. It provides an authentication system for a network of machines - much like Sun's Network Information Service or LDAP. Kerberos is an authentication system only - it can identify the entity requesting resources to the server, but it cannot do authorization. That has to be implemented at each individual server. If for example, in a system that uses Kerberos authentication, a user A authenticates himself and requests resource R on machine M1, then M1 has to be set up to authorize A to access R on M1. If R is a shared resource that's available on machine M2 also, then M2 has to explicitly authorize A to access resource R. Kerberos does not provide a way to allow one to share authorization settings across its domain. DCE can. It does this by supporting Access Control Lists (ACLs). Kerberos is a computer network authentication protocol which allows individuals communicating over an insecure network to prove their identity to one another in a secure manner. ... The Network Information Service or NIS is Sun Microsystems Yellow Pages (YP) client-server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network. ... In computer networking, the Lightweight Directory Access Protocol, or LDAP, is a networking protocol for querying and modifying directory services running over TCP/IP. An LDAP directory usually follows the X.500 model: It is a tree of entries, each of which consists of a set of named attributes with... The access control list (ACL) is a concept in computer security used to enforce privilege separation. ...

The largest unit of management in DCE is a cell. The highest privileges within a cell are assigned to a role called cell administrator. Typically this privileges are held by a DCE principal called cell_admin. Note that this need not be a real OS-level user. The cell_admin has all privileges over all DCE resources within the cell. Privileges can be awarded to or removed from the following categories : user_obj, group_obj, other_obj, any_other for any given DCE resource. The first three correspond to the owner, group member, and any other DCE principal respectively. The last group contains any non-DCE principal. Multiple cells can be configured to communicate and share resources with each other. All principals from external cells are treated as "foreign" users and privileges can be awarded / removed accordingly. In addition to this, specific users or groups can be assigned privileges on any DCE resource - something which is not possible with the traditional UNIX filesystem.

There are three major components of DCE within every cell: (1) the security server (which is responsible for authentication) (2) The Cell Directory Server (CDS) (which is the respository of resources and ACLs) and (3) The Distributed Time Server which provides an accurate clock for proper functioning of the entire cell. Modern DCE implementations such as IBM's are fully capable of interoperating with Kerberos as the security server, LDAP for the CDS and the Network Time Protocol implementations for the time server. The Network Time Protocol (NTP) is a protocol for synchronising the clocks of computer systems over packet-switched, variable-latency data networks. ...

While it is possible to implement a distributed file system using plain old DCE by defining files to the CDS and defining the appropriate ACLs on them, this is not user-friendly. DCE/DFS (Distributed Filesystem - not to be confused with the Microsoft product called DFS which is NOT interoperable with DCE) is a DCE based application which provides a distributed filesystem on DCE. DCE/DFS can support replicas of a fileset (the DCE/DFS equivalent of a filesystem) on multiple DFS servers - there is one read-write copy and zero or more read only copies. Replication is supported between the read-write and the read-only copies. In addition, DCE/DFS also supports what are called "backup" filesets, which if defined for a fileset are capable of storing a version of the fileset as it was prior to the last replication. The Microsoft Distributed File System, or DFS, is a set of client and server services that allow a large enterprise to organize many distributed file shares into a distributed file system. ...

DCE/DFS is believed to be the world's only distributed filesystem that correctly implements the full POSIX filesystem semantics - including byte range locking. DCE/DFS was sufficiently reliable and stable to be utilised by IBM to run the back-end filesystem for the 1996 Olympics web site, seamlessly and automatically distributed (and edited!) worldwide in different timezones. International Business Machines Corporation (IBM, or colloquially, Big Blue) NYSE: IBM (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, NY, USA. The company manufactures and sells computer hardware, software, infrastructure services and consulting services. ...

External links

• The Open Group's DCE Portal
• DCE description at Carnegie Mellon's Software Engineering Institute