# Version Control System

Version control is the art of managing changes to information. It has long been a critical tool for programmers, who typically spend their time making small changes to software and then undoing those changes the next day. But the usefulness of version control software extends far beyond the bounds of the software development world. Anywhere you can find people using computers to manage information that changes often, there is room for version control.

## Bazaar

Bazaar is a new version control system sponsored by Canonical, the commercial company behind Ubuntu. Unlike Subversion and CVS that only support a central repository model, Bazaar also supports distributed version control, giving people the ability to collaborate more efficiently. In particular, Bazaar is designed to maximize the level of community participation in open source projects.

### Installation

At a terminal prompt, enter the following command to install bzr:

    sudo apt-get install bzr

### Configuration

To introduce yourself to bzr, use the whoami command like this:

    $ bzr whoami 'Joe Doe <joe.doe@gmail.com>'

### Learning Bazaar

Bazaar comes with bundled documentation installed into /usr/share/doc/bzr/html by default. The tutorial is a good place to start. The bzr command also comes with built-in help:

    $ bzr help

To learn more about the foo command:

    $ bzr help foo

### Launchpad Integration

While highly useful as a stand-alone system, Bazaar has good, optional integration with Launchpad, the collaborative development system used by Canonical and the broader open source community to manage and extend Ubuntu itself. For information on how Bazaar can be used with Launchpad to collaborate on open source projects, see http://bazaar-vcs.org/LaunchpadIntegration.

## Subversion

Subversion is an open source version control system. Using Subversion, you can record the history of source files and documents. It manages files and directories over time. A tree of files is placed into a central repository. The repository is much like an ordinary file server, except that it remembers every change ever made to files and directories.

### Installation

To access Subversion repository using the HTTP protocol, you must install and configure a web server. Apache2 is proven to work with Subversion. Please refer to the HTTP subsection in the Apache2 section to install and configure Apache2. To access the Subversion repository using the HTTPS protocol, you must install and configure a digital certificate in your Apache 2 web server. Please refer to the HTTPS subsection in the Apache2 section to install and configure the digital certificate.

To install Subversion, run the following command from a terminal prompt:

    sudo apt-get install subversion libapache2-svn

### Server Configuration

This step assumes you have installed above mentioned packages on your system. This section explains how to create a Subversion repository and access the project.

#### Create Subversion Repository

The Subversion repository can be created using the following command from a terminal prompt:

    svnadmin create /path/to/repos/project

#### Importing Files

Once you create the repository you can import files into the repository. To import a directory, enter the following from a terminal prompt:

    svn import /path/to/import/directory file:///path/to/repos/project

### Access Methods

Subversion repositories can be accessed (checked out) through many different methods --on local disk, or through various network protocols. A repository location, however, is always a URL. The table describes how different URL schemes map to the available access methods.

Access Methods

Schema | Access Method
--- | ---
file:// | direct repository access (on local disk)
http:// | Access via WebDAV protocol to Subversion-aware Apache2 web server
https:// | Same as http://, but with SSL encryption
svn:// | Access via custom protocol to an svnserve server
svn+ssh:// | Same as svn://, but through an SSH tunnel

In this section, we will see how to configure Subversion for all these access methods. Here, we cover the basics. For more advanced usage details, refer to the svn book.

#### Direct repository access (file://)

This is the simplest of all access methods. It does not require any Subversion server process to be running. This access method is used to access Subversion from the same machine. The syntax of the command, entered at a terminal prompt, is as follows:

    svn co file:///path/to/repos/project

or

    svn co file://localhost/path/to/repos/project

If you do not specify the hostname, there are three forward slashes (///) -- two for the protocol (file, in this case) plus the leading slash in the path. If you specify the hostname, you must use two forward slashes (//).

The repository permissions depend on filesystem permissions. If the user has read/write permission, he can checkout from and commit to the repository.

#### Access via WebDAV protocol (http://)

To access the Subversion repository via WebDAV protocol, you must configure your Apache 2 web server. Add the following snippet between the <VirtualHost> and </VirtualHost> elements in `/etc/apache2/sites-available/default`, or another VirtualHost file:

     <Location /svn>
      DAV svn
      SVNPath /home/svn
      AuthType Basic
      AuthName "Your repository name"
      AuthUserFile /etc/subversion/passwd
      Require valid-user
     </Location>

The above configuration snippet assumes that Subversion repositories are created under `/home/svn/` directory using `svnadmin` command. They can be accessible using `http://hostname/svn/repos_name` url.

To import or commit files to your Subversion repository over HTTP, the repository should be owned by the HTTP user. In Ubuntu systems, normally the HTTP user is `www-data`. To change the ownership of the repository files enter the following command from terminal prompt:

    sudo chown -R www-data:www-data /path/to/repos

By changing the ownership of repository as `www-data` you will not be able to import or commit files into the repository by running `svn import file:///` command as any user other than `www-data`.

Next, you must create the `/etc/subversion/passwd` file that will contain user authentication details. To create a file issue the following command at a command prompt (which will create the file and add the first user):

    sudo htpasswd -c /etc/subversion/passwd user_name

To add additional users omit the "-c" option as this option replaces the old file. Instead use this form:

    sudo htpasswd /etc/subversion/password user_name

This command will prompt you to enter the password. Once you enter the password, the user is added. Now, to access the repository you can run the following command:

    svn co http://servername/svn

The password is transmitted as plain text. If you are worried about password snooping, you are advised to use SSL encryption. For details, please refer next section.

#### Access via WebDAV protocol with SSL encryption (https://)

Accessing Subversion repository via WebDAV protocol with SSL encryption (https://) is similar to http:// except that you must install and configure the digital certificate in your Apache2 web server. To use SSL with Subversion add the above Apache2 configuration to `/etc/apache2/sites-available/default-ssl`. For more information on setting up Apache2 with SSL see .

You can install a digital certificate issued by a signing authority. Alternatively, you can install your own self-signed certificate.

This step assumes you have installed and configured a digital certificate in your Apache 2 web server. Now, to access the Subversion repository, please refer to the above section! The access methods are exactly the same, except the protocol. You must use https:// to access the Subversion repository.

#### Access via custom protocol (svn://)

Once the Subversion repository is created, you can configure the access control. You can edit the `/path/to/repos/project/conf/svnserve.conf` file to configure the access control. For example, to set up authentication, you can uncomment the following lines in the configuration file:

    # [general]
    # password-db = passwd

After uncommenting the above lines, you can maintain the user list in the passwd file. So, edit the file `passwd` in the same directory and add the new user. The syntax is as follows:

    username = password

For more details, please refer to the file.

Now, to access Subversion via the svn:// custom protocol, either from the same machine or a different machine, you can run svnserver using svnserve command. The syntax is as follows:

    $ svnserve -d --foreground -r /path/to/repos
    # -d -- daemon mode
    # --foreground -- run in foreground (useful for debugging)
    # -r -- root of directory to serve

    For more usage details, please refer to:
    $ svnserve --help

Once you run this command, Subversion starts listening on default port (3690). To access the project repository, you must run the following command from a terminal prompt:

    svn co svn://hostname/project project --username user_name

Based on server configuration, it prompts for password. Once you are authenticated, it checks out the code from Subversion repository. To synchronize the project repository with the local copy, you can run the `update` sub-command. The syntax of the command, entered at a terminal prompt, is as follows:

    cd project_dir ; svn update

For more details about using each Subversion sub-command, you can refer to the manual. For example, to learn more about the co (checkout) command, please run the following command from a terminal prompt:

    svn co help

#### Access via custom protocol with SSL encryption (svn+ssh://)

The configuration and server process is same as in the svn:// method. For details, please refer to the above section. This step assumes you have followed the above step and started the Subversion server using svnserve command.

It is also assumed that the ssh server is running on that machine and that it is allowing incoming connections. To confirm, please try to login to that machine using ssh. If you can login, everything is perfect. If you cannot login, please address it before continuing further.

The svn+ssh:// protocol is used to access the Subversion repository using SSL encryption. The data transfer is encrypted using this method. To access the project repository (for example with a checkout), you must use the following command syntax:

    svn co svn+ssh://hostname/var/svn/repos/project

You must use the full path (/path/to/repos/project) to access the Subversion repository using this access method.

Based on server configuration, it prompts for password. You must enter the password you use to login via ssh. Once you are authenticated, it checks out the code from the Subversion repository.

## CVS Server

CVS is a version control system. You can use it to record the history of source files.

### Installation

To install CVS, run the following command from a terminal prompt:

    sudo apt-get install cvs

After you install cvs, you should install xinetd to start/stop the cvs server. At the prompt, enter the following command to install xinetd:

    sudo apt-get install xinetd

### Configuration

Once you install cvs, the repository will be automatically initialized. By default, the repository resides under the /var/lib/cvs directory. You can change this path by running following command:

    cvs -d /your/new/cvs/repo init

Once the initial repository is set up, you can configure xinetd to start the CVS server. You can copy the following lines to the `/etc/xinetd.d/cvspserver` file.

    service cvspserver
    {
         port = 2401
         socket_type = stream
         protocol = tcp
         user = root
         wait = no
         type = UNLISTED
         server = /usr/bin/cvs
         server_args = -f --allow-root /var/lib/cvs pserver
         disable = no
    }

Be sure to edit the repository if you have changed the default repository (/var/lib/cvs) directory.

Once you have configured xinetd you can start the cvs server by running following command:

    sudo /etc/init.d/xinetd restart

You can confirm that the CVS server is running by issuing the following command:

    sudo netstat -tap | grep cvs

When you run this command, you should see the following line or something similar:

    tcp        0      0 *:cvspserver            *:* LISTEN

From here you can continue to add users, add new projects, and manage the CVS server.

CVS allows the user to add users independently of the underlying OS installation. Probably the easiest way is to use the Linux Users for CVS, although it has potential security issues. Please refer to the CVS manual for details.

### Add Projects

This section explains how to add new project to the CVS repository. Create the directory and add necessary document and source files to the directory. Now, run the following command to add this project to CVS repository:

    cd your/project
    cvs -d :pserver:username@hostname.com:/var/lib/cvs import -m "Importing my project to CVS repository" . new_project start

You can use the CVSROOT environment variable to store the CVS root directory. Once you export the CVSROOT environment variable, you can avoid using -d option in the above cvs command.

The string new_project is a vendor tag, and start is a release tag. They serve no purpose in this context, but since CVS requires them, they must be present.

When you add a new project, the CVS user you use must have write access to the CVS repository (/var/lib/cvs). By default, the src group has write access to the CVS repository. So, you can add the user to this group, and he can then add and manage projects in the CVS repository.

## References

Bazaar Home Page

Launchpad

Subversion Home Page

Subversion Book

CVS Manual

Easy Bazaar Ubuntu Wiki page

Ubuntu Wiki Subversion page