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Supporting Multiple Repository Access Methods

You've seen how a repository can be accessed in many different ways. But is it possible—or safe—for your repository to be accessed by multiple methods simultaneously? The answer is yes, provided you use a bit of foresight.

At any given time, these processes may require read and write access to your repository:

The most common problem administrators run into is repository ownership and permissions. Does every process (or user) in the preceding list have the rights to read and write the repository's underlying data files? Assuming you have a Unix-like operating system, a straightforward approach might be to place every potential repository user into a new svn group, and make the repository wholly owned by that group. But even that's not enough, because a process may write to the database files using an unfriendly umask—one that prevents access by other users.

So the next step beyond setting up a common group for repository users is to force every repository-accessing process to use a sane umask. For users accessing the repository directly, you can make the svn program into a wrapper script that first runs umask 002 and then runs the real svn client program. You can write a similar wrapper script for the svnserve program, and add a umask 002 command to Apache's own startup script, apachectl. For example:

$ cat /usr/bin/svn


umask 002
/usr/bin/svn-real "$@"

Another common problem is often encountered on Unix-like systems. If your repository is backed by Berkeley DB, for example, it occasionally creates new log files to journal its actions. Even if the Berkeley DB repository is wholly owned by the svn group, these newly created log files won't necessarily be owned by that same group, which then creates more permissions problems for your users. A good workaround is to set the group SUID bit on the repository's db directory. This causes all newly created log files to have the same group owner as the parent directory.

Once you've jumped through these hoops, your repository should be accessible by all the necessary processes. It may seem a bit messy and complicated, but the problems of having multiple users sharing write access to common files are classic ones that are not often elegantly solved.

Fortunately, most repository administrators will never need to have such a complex configuration. Users who wish to access repositories that live on the same machine are not limited to using file:// access URLs—they can typically contact the Apache HTTP server or svnserve using localhost for the server name in their http:// or svn:// URL. And maintaining multiple server processes for your Subversion repositories is likely to be more of a headache than necessary. We recommend that you choose a single server that best meets your needs and stick with it!