1. What is CVS?

For example, bugs sometimes creep in when software is modified, and you might not detect the bug until a long time after you make the modification. With cvs, you can easily retrieve old versions to see exactly which change caused the bug. This can sometimes be a big help.

You could of course save every version of every file you have ever created. This would however waste an enormous amount of disk space. cvs stores all the versions of a file in a single file in a clever way that only stores the differences between versions.

cvs also helps you if you are part of a group of people working on the same project. It is all too easy to overwrite each others' changes unless you are extremely careful. Some editors, like gnu Emacs, try to make sure that the same file is never modified by two people at the same time. Unfortunately, if someone is using another editor, that safeguard will not work. cvs solves this problem by insulating the different developers from each other. Every developer works in his own directory, and cvs merges the work when each developer is done.

cvs started out as a bunch of shell scripts written by Dick Grune, posted to comp.sources.unix in the volume 6 release of December, 1986. While no actual code from these shell scripts is present in the current version of cvs much of the cvs conflict resolution algorithms come from them.

In April, 1989, Brian Berliner designed and coded cvs. Jeff Polk later helped Brian with the design of the cvs module and vendor branch support.

You can get cvs via anonymous ftp from a number of sites, for instance prep.ai.mit.edu in pub/gnu.

There is a mailing list for cvs where bug reports can be sent, questions can be asked, an FAQ is posted, and discussion about future enhancements to cvs take place. To submit a message to the list, write to <info-cvs@prep.ai.mit.edu>. To subscribe or unsubscribe, write to <info-cvs-request@prep.ai.mit.edu>. Please be specific about your email address.

Work is in progress on creating a newsgroup for cvs-related topics. It will appear somewhere under the `gnu.' hierarchy. Gateways to and from the mailing list will be set up. The ftp site think.com has some cvs material in the /pub/cvs subdirectory. Currently (late summer 1993) it contains an excellent faq (Frequently Asked Questions, with answers), and an improved (but unofficial) version of cvs.

CVS is not...

cvs is not a build system.

Though the structure of your repository and modules file interact with your build system (e.g. Makefiles), they are essentially independent.

cvs does not dictate how you build anything. It merely stores files for retrieval in a tree structure you devise.

cvs does not dictate how to use disk space in the checked out working directories. If you write your Makefiles or scripts in every directory so they have to know the relative positions of everything else, you wind up requiring the entire repository to be checked out. That's simply bad planning.

If you modularize your work, and construct a build system that will share files (via links, mounts, VPATH in Makefiles, etc.), you can arrange your disk usage however you like.

But you have to remember that any such system is a lot of work to construct and maintain. cvs does not address the issues involved. You must use your brain and a collection of other tools to provide a build scheme to match your plans.

Of course, you should place the tools created to support such a build system (scripts, Makefiles, etc) under cvs.

cvs is not a substitute for management.

Your managers and project leaders are expected to talk to you frequently enough to make certain you are aware of schedules, merge points, branch names and release dates. If they don't, cvs can't help.

cvs is an instrument for making sources dance to your tune. But you are the piper and the composer. No instrument plays itself or writes its own music.

cvs is not a substitute for developer communication.

When faced with conflicts within a single file, most developers manage to resolve them without too much effort. But a more general definition of ``conflict'' includes problems too difficult to solve without communication between developers.

cvs cannot determine when simultaneous changes within a single file, or across a whole collection of files, will logically conflict with one another. Its concept of a conflict is purely textual, arising when two changes to the same base file are near enough to spook the merge (i.e. diff3) command.

cvs does not claim to help at all in figuring out non-textual or distributed conflicts in program logic.

For example: Say you change the arguments to function X defined in file A. At the same time, someone edits file B, adding new calls to function X using the old arguments. You are outside the realm of cvs's competence.

Acquire the habit of reading specs and talking to your peers.

cvs is not a configuration management system.

cvs is a source control system. The phrase ``configuration management'' is a marketing term, not an industry-recognized set of functions.

A true ``configuration management system'' would contain elements of the following:

• Source control.
• Dependency tracking.
• Build systems (i.e. What to build and how to find things during a build. What is shared? What is local?)
• Bug tracking.
• Automated Testing procedures.
• Release Engineering documentation and procedures.
• Tape Construction.
• Customer Installation.
• A way for users to run different versions of the same software on the same host at the same time.

cvs provides only the first.