Server Configuration

write permissions appropriately. If you know which user(s) svnserve will run as, restrict read access to the user file as necessary.

Set access controls

There are two more variables to set in the svnserve.conf file: they determine what unauthenticated (anonymous) and authenticated users are allowed to do. The variables anon-access and auth-access can be set to the values none, read, or write. Setting the value to none restricts all access of any kind; read allows read-only access to the repository, and write allows complete read/write access to the repository. For example:

[general]

password-db = userfile realm = example realm

#anonymous users can only read the repository anon-access = read

#authenticated users can both read and write auth-access = write

The example settings are, in fact, the default values of the variables, should you forget to define them. If you want to be even more conservative, you can block anonymous access completely:

[general]

password-db = userfile realm = example realm

#anonymous users aren't allowed anon-access = none

#authenticated users can both read and write auth-access = write

Notice that svnserve only understands “blanket” access control. A user either has universal read/write access, universal read access, or no access. There is no detailed control over access to specific paths within the repository. For many projects and sites, this level of access control is more than adequate. However, if you need per-directory access control, you'll need to use either use Apache with mod_authz_svn (see the section called “Per-Directory Ac- cess Control”) or use a pre-commit hook script to control write access (see the section called “Hook Scripts”). The Subversion distribution comes with commit-access-control.pl and the more sophisticated svnperms.py scripts for use in pre-commit scripts.

SSH authentication and authorization

svnserve's built-in authentication can be very handy, because it avoids the need to create real system accounts. On the other hand, some administrators already have well-established SSH authentication frameworks in place. In these situations, all of the project's users already have system accounts and the ability to “SSH into” the server machine.

It's easy to use SSH in conjunction with svnserve. The client simply uses the svn+ssh:// URL schema to connect:

$ whoami harry

$ svn list svn+ssh://host.example.com/repos/project harry@host.example.com's password: *****

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Server Configuration

foo bar baz

…

In this example, the Subversion client is invoking a local ssh process, connecting to host.example.com, authenticating as the user harry, then spawning a private svnserve process on the remote machine running as the user harry. The svnserve command is being invoked in tunnel mode (-t) and its network protocol is being tun- “neled” over the encrypted connection by ssh, the tunnel-agent. svnserve is aware that it's running as the user harry, and if the client performs a commit, the authenticated username will be attributed as the author of the new revision.

The important thing to understand here is that the Subversion client is not connecting to a running svnserve daemon. This method of access doesn't require a daemon, nor does it notice one if present. It relies wholly on the ability of ssh to spawn a temporary svnserve process, which then terminates when the network connection is closed.

When using svn+ssh:// URLs to access a repository, remember that it's the ssh program prompting for authentication, and not the svn client program. That means there's no automatic password caching going on (see the section called “Client Credentials Caching”). The Subversion client often makes multiple connections to the repository, though users don't normally notice this due to the password caching feature. When using svn+ssh:// URLs, however, users may be annoyed by ssh repeatedly asking for a password for every outbound connection. The solution is to use a separate SSH password-caching tool like ssh-agent on a Unix-like system, or pageant on Windows.

When running over a tunnel, authorization is primarily controlled by operating system permissions to the repository's database files; it's very much the same as if Harry were accessing the repository directly via a file:/// URL. If multiple system users are going to be accessing the repository directly, you may want to place them into a common group, and you'll need to be careful about umasks. (Be sure to read the section called “Supporting Multiple Repository Access Methods”.) But even in the case of tunneling, the svnserve.conf file can still be used to block access, by simply setting auth-access = read or auth-access = none.

You'd think that the story of SSH tunneling would end here, but it doesn't. Subversion allows you to create custom tunnel behaviors in your run-time config file (see the section called “Runtime Configuration Area”.) For example, suppose you want to use RSH instead of SSH. In the [tunnels] section of your config file, simply define it like this:

[tunnels] rsh = rsh

And now, you can use this new tunnel definition by using a URL schema that matches the name of your new variable: svn+rsh://host/path. When using the new URL schema, the Subversion client will actually be running the command rsh host svnserve -t behind the scenes. If you include a username in the URL (for example, svn+rsh://username@host/path) the client will also include that in its command (rsh username@host svnserve -t.) But you can define new tunneling schemes to be much more clever than that:

[tunnels]

joessh = $JOESSH /opt/alternate/ssh -p 29934

This example demonstrates a couple of things. First, it shows how to make the Subversion client launch a very specific tunneling binary (the one located at /opt/alternate/ssh) with specific options. In this case, accessing a svn+joessh:// URL would invoke the particular SSH binary with -p 29934 as arguments—useful if you want the tunnel program to connect to a non-standard port.

Second, it shows how to define a custom environment variable that can override the name of the tunneling program. Setting the SVN_SSH environment variable is a convenient way to override the default SSH tunnel agent. But if you need to have several different overrides for different servers, each perhaps contacting a different port or passing a different set of options to SSH, you can use the mechanism demonstrated in this example. Now if we were to set the

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