[olug] CVS

Fri Sep 12 19:48:04 UTC 2003

At Fri, 12 Sep 03, Unidentified Flying Banana Craig Wolf, said:

> Ok, pardon my ignorance.  What is CVS, where do I get it (freshmeat?),
> what does it do for me?  Tracks changes in files I tell it to watch??
> I am trying to understand.  I am still standing on the edge of this
> ocean and I am only up to my ankles so far in crossing it.  

CVS is the software package, the Concurrent Versions System[1].  It is
built on top of the concepts from Revision Control System (RCS), and it
is a type of Source Configuration (or Control) Management (SCM)
software.

Basically, every time you make a change to a file, you 'check in' the
changes, and they are recorded.  In this way, any changes you make can
be reversed and tracked.  The most common use for these types of systems
is in software development and programming.  By keeping your source code
in something like CVS, you can make it *much* easier for multiple people
to each be working on the same software.  

Here's a quick and dirty example. . . say I'm writing a program called
'foo'.  The first thing I do, is take any source code files (and other
related development files) and put them into my CVS system.  I do that
by creating a CVS repository and importing everything I currently have.

Then, every time I make changes to any file, I check in the changes, and
the changes are recorded in the CVS repository (as a diff, basically).

Additionally, since CVS is network transparent, and can be used as a
client-server system, I don't have to work on it at a single location.
Once my changes have been checked into the CVS repository, I could then
go to another computer, check out the entire source code set, and work
on it there.  If I then make changes, and check them in, I could later
go back to my original computer and update my local code to match the
'current' code that is in the CVS repository.

Through this way, by having a central repository that tracks all the
changes, but having multiple "working" copies checked out, many people
can all be working on the same code.

You can also tag sets of files and versions as a set.  For example, if
I'm working on foo, as mentioned above, and we hit version 1.0, I could
tag the CVS repository to foo_release_1_0.  Then, even if we work on the
program for two more years, if I get a sudden desire to see how the code
looked at version one, I could retrieve it by simply getting all the
files that have that tag, at the version tagged.

And, as you can probably imagine, the software works great for any files
that change frequently.  I keep all of /etc in CVS, and every time I
make any changes, I check in those changes.  If I make really big
changes, for example, moving from Apache 1.x to 2.x, I even tag the
httpd.conf, since there are major changes to it, as
apache_1_last_config.  Then, if six months from now I decide to suddenly
go back to Apache 1.x, I can easily retrieve that specific version of
the file.

If you ever change a conf file, and accidentally make a change that
breaks it, and the program won't start, you could be in a bad spot.
Especially if you made a lot of changes, and don't know where it's
broken at.  In this case, it would be easiest to just pull out the last
checked in version of the file, and use that, while you play with the
new one.  Same thing if you accidentally delete a conf file.  You can
simply pull the last checked in version from CVS.

I'm not sure if I'm doing a very good job explaining this. . . I've been
using CVS intensely for so long that I may not be the best person for
this.  However, there are a number of great resources available for it.

  * There's the Cederqvist manual[2], which was written by Per
    Cederqvist et al, and is the "official" CVS manual.
  * There's the CVS FAQ-O-Matic[3], which contains a lot of great Q&A for
    CVS.
  * There's the book, "Open Source Development with CVS", by Karl Fogel
    and Moshe Bar.
    - The first edition[4] is almost entirely freely available, and can
      be found online.
    - The newer Second edition[5] is also available, but only in PDF
      format.  If you don't mind PDF, I'd suggest it, as it has a little
      more information in it.

My suggestion would be to start with the Second Edition of the CVS book
(the PDF), but any of those should be able to provide you with more
information.

As for getting CVS, most distributions include it either by default, or
as part of their "development tools", if you install that.  On Debian,
it's as easy as 'apt-get install cvs'. ;-)

If you can't find it as part of your distribution, you can get it from
their homepage, which is referenced in this e-mail.

> Thanx to any and all for replies!

Hope this helps. ;-)

If you have any other questions, or would like a better explanation of
how I set up /etc in CVS, let me know.

> Craig Wolf

 [1] http://www.cvshome.org/
 [2] http://www.cvshome.org/docs/manual/
 [3] http://ccvs.cvshome.org/fom//cache/1.html
 [4] http://cvsbook.red-bean.com/cvsbook.html
 [5] http://cvsbook.red-bean.com/OpenSourceDevWithCVS_2E.tar.gz

-- 
| Christopher
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| A: No.                                         |
| Q: Should I include quotations after my reply? |
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