Is there a graceful way to stop svnserve -d

The recommended way is to do it is by using the kill command which will allow subversion to shut down properly. I don't think there is any better way to do it.

you can use the command : ps aux | grep svnserve to get the svnserve process ID
then : kill -9 [ID_of_svnserve_process]

You can use the start-stop-daemon program to do it :

/sbin/start-stop-daemon --stop --exec /usr/bin/svnserve

To start it :

 /sbin/start-stop-daemon --start --chuid svn:svn --exec /usr/bin/svnserve -- -d -r /var/svn

Of course you can adapt user and group (svn:svn), and the SVN root path (/var/svn)

These scripts are part of another one located in /etc/init.d/svnserve that I use on all my SVN servers to manage the daemon. See this Ubuntu doc for more explanations.