Concurrent Versions System |
The Concurrent Versions System (CVS), also known as the Concurrent Versioning System, implements a .
= Features =
CVS utilizes a platform.
Several clients may edit copies of the project concurrently. When they later check-in their changes, the server attempts to merge them. If this fails, for instance because two clients attempted to change the same line in a certain file, then the server denies the second check-in operation and informs the client about the conflict, which the user will need to resolve by hand. If the check-in operation succeeds, then the version numbers of all files involved automatically increment, and the CVS server writes a user-supplied description line, the date and the author s name to its data logging files.
Clients can also compare different versions of files, request a complete history of changes, or check-out a historical snapshot of the project as of a given date or as of a revision number. Many open source projects allow anonymous read access, a feature that was pioneered by OpenBSD. This means that clients may check-out and compare versions with either a blank or simple published password (e.g anoncvs ); only the check-in of changes requires a personal account and password in these scenarios.
Clients can also use the update command in order to bring their local copies up-to-date with the newest version on the server. This eliminates the need for repeated downloading of the whole project.
CVS can also maintain different branches of a project. For instance, a released version of the software project may form one branch, used for bug fixes, while a version under current development, with major changes and new features, forms a separate branch.
CVS uses delta compression for efficient storage of different versions of the same file.
= Terminology =
CVS terminology dubs a single project (set of related files) managed by CVS as a module . A CVS server can manage several modules; it stores all the modules it manages in its Repository . The copy of a module that a client can check out serves as a working copy and reflects recent changes other clients Commit_(data_management) to the module . Update is the process of acquiring latest changes from Repository to the working copy .
= History and status =
CVS developed from an earlier versioning system called Revision Control System (RCS), still in use, which manages individual files but not whole projects. Dick Grune has provided some [http://www.cs.vu.nl/~dick/CVS.html#History brief historical notes] about CVS on his site. To quote:
The code was publicly released to mod.sources on .
The code that eventually evolved into the current version of CVS started with Brian Berliner in April 1989, with later input from Jeff Polk and many other contributors. Brian Berliner wrote [http://citeseer.ist.psu.edu/berliner90cvs.html a paper introducing his improvements to the CVS program] which describes how the tool was extended and used internally by Prisma, a third party developer working on the SunOS kernel, and was released for the benefit of the community under the GPL.
Nowadays, a group of volunteers maintains the CVS code. Notably, the development of the Microsoft Windows version of CVS has split off into a separate project named CVSNT and has been more active in extending the feature set of the system, even porting the changes back to the UNIX platform under the name CVSNT.
Historically, the relationship between CVS and the GNU project could appear somewhat ambiguous: the GNU website distributed the program, labelling it GNU package on one page and other GPL-licensed project on another. This was recently clarified when CVS development moved from cvshome.org to savannah.nongnu.org, with CVS officially assigned to the non-gnu category. On the FTP site, the program has traditionally and still does reside in the /non-gnu/ directory.
=Limitations=
Users unhappy with these limitations began the development of CVSNT and released the first version in 1999 replacing CVS. Linux and Unix support was re-added in early 2002, rename, Unicode and change management support was added in 2004.
A number of key developers who have worked on CVS are now responsible for Subversion (software) (SVN), released in early 2004, which aims to replace CVS by addressing some of its limitations.
=See also=
=External links=
=Literature=
*March Hare Software: All About CVS: How to Design and Build an Effective CM solution using TortoiseCVS, WinCVS, Bugzilla on Windows and Linux (2005), [http://www.march-hare.com/cvsnt/features/book/ purchase eBook online] *David A. Thomas (Software), Andrew Hunt: Pragmatic Version Control Using CVS (The Pragmatic Programmers, 2003), ISBN 0-9745140-0-4 *Jennifer Vesperman: Essential CVS (O Reilly, 2003), ISBN 0-596-00459-1 *Per Cederqvist et al: Version Management with CVS , ISBN 0-9541617-1-8, [http://www.network-theory.co.uk/cvs/manual/ Official reference manual] *Karl Franz Fogel, Moshe Bar: Open Source Development with CVS , ISBN 1-932111-81-6, [http://cvsbook.red-bean.com/ online]|
|