Concurrent Versions System (CVS, or Concurrent Versioning System) is a
version control system originally developed by
Dick Grune in July 1986.
Design
CVS operates as a
front end to
Revision Control System (RCS), an older version control system that manages individual files but not whole projects. It expands upon RCS by adding support for repository-level change tracking, and a client-server model.
Files are tracked using the same history format as in RCS, with a
hidden directory containing a corresponding history file for each file in the repository.
CVS uses
delta compression for efficient storage of different versions of the same file. This works well with large text files with few changes from one version to the next. This is usually the case for source code files. On the other hand, when CVS is told to store a file as binary, it will keep each individual version on the server. This is typically used for non-text files such as executable images where it is difficult to create compact deltas between versions.
CVS excludes
symbolic link
In computing, a symbolic link (also symlink or soft link) is a file whose purpose is to point to a file or directory (called the "target") by specifying a path thereto.
Symbolic links are supported by POSIX and by most Unix-like operating syste ...
s because when they are stored in a version control system they can pose a security risk. For instance, a symbolic link to a sensitive file can be stored in the repository, making the sensitive file accessible even when it is not checked in. In place of symbolic links, scripts that require certain privileges and conscious intervention to execute may be checked into CVS.
Operation
CVS labels a single project (set of related files) that it manages as a ''
module''. A CVS server stores the modules it manages in its ''
repository''. Programmers acquire copies of modules by ''checking out''. The checked-out files serve as a ''working copy'', ''sandbox'' or ''workspace''. Changes to the working copy are reflected in the repository by ''
committing'' them. To ''update'' is to acquire or ''
merge'' the changes in the repository with the working copy.
CVS uses a
client–server architecture: a server stores the current version(s) of a
project
A project is a type of assignment, typically involving research or design, that is carefully planned to achieve a specific objective.
An alternative view sees a project managerially as a sequence of events: a "set of interrelated tasks to be ...
and its history, and clients connect to the server in order to "check out" a complete copy of the project, work on this copy and then later "check in" their changes. CVS servers can allow "anonymous read access",
wherein 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. Several developers may work on the same project concurrently, each one editing files within their own "working copy" of the project, and sending (or ''checking in'') their modifications to the server. To avoid conflicts, the server only accepts changes made to the most recent version of a file. Developers are therefore expected to keep their working copy up-to-date by incorporating other people's changes on a regular basis. This task is mostly handled automatically by the CVS client, requiring manual intervention only when an
edit conflict arises between a checked-in modification and the yet-unchecked local version of a file. Clients can also use the "update" command to bring their local copies up-to-date with the newest version on the server. Clients can also compare versions, request a complete history of changes, or check out a historical snapshot of the project (e.g.: based on a given date). If the check-in operation succeeds, then the version numbers of all files involved automatically increment, and the server writes a user-supplied description line, the date and the author's name to its
log files. CVS can also run external, user-specified log processing scripts following each commit. These scripts are installed by an entry in CVS's
loginfo
file, which can trigger email notification or convert the log data into a Web-based format.
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, can form a separate branch. CVS assumes that the majority of work takes place on the trunk, and that branches should generally be short-lived or historical. When used as designed, branches are easily managed and branch operations are efficient and fast.
Portability
The server software normally runs on
Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
(although at least the
CVSNT server also supports various flavors of
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
), while CVS clients may run on any major
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
platform.
History
Grune recalled:
Grune publicly released the code on June 23, 1986.
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 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.
On November 19, 1990, CVS version 1.0 was submitted to the
Free Software Foundation
The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985. The organisation supports the free software movement, with the organization's preference for software being distributed ...
for development and distribution.
The latest version was released on 8 May 2008.
Adoption and successors
Over time, developers have created new version control systems based on CVS in order to add features, alter the operational model, and improve developers' productivity. CVS replacement projects include
CVSNT and
Subversion
Subversion () refers to a process by which the values and principles of a system in place are contradicted or reversed in an attempt to sabotage the established social order and its structures of Power (philosophy), power, authority, tradition, h ...
.
See also
*
Comparison of version-control software
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Cervisia
*
OpenGrok
*
TortoiseCVS
*
ViewVC
Notes
References
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External links
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{{Authority control
1990 software
Free software programmed in C
Free version control software
Software using the GNU General Public License
Unix archivers and compression-related utilities