There are a couple of ways to shutdown a voltdb server or cluster without ctrl-c or kill -9. The enterprise edition has a tool called Volt Enterprise Manager that can gracefully close a cluster. You can also do it in a somewhat more manual way depending on whether you want to save the data you've been working with.
The manual method to first start sqlcmd and exec @Shutdown;
This will shutdown the VoltDB node that sqlcmd is connected to at the time.
If you want to save your data then run these two commands:
exec @SnapshotSave ;
That will save a snapshot and shutdown VoltDB.
Finally, you can connect to the admin port with sqlcmd and run these commands:
@Pause will pause the db and block new transactions. @SnapshotSave will save the state of the database. @Shutdown will close VoltDB.
Look at http://community.voltdb.com/docs/UsingVoltDB/AppSysProc
for sysproc information
Look at http://community.voltdb.com/docs/UsingVoltDB/ChapAppRun
for more detailed information on saving and restoring a cluster. These also talk about how to connect to the admin port.