Critical Description
HBase init scripts, like all Hadoop init scripts, are killed at the same time (K20-*) in /etc/rc0.d and /etc/rc6.d.
If the HMaster and/or the datanode shuts down before the regionserver, this causes the regionserver to take a long time to actually give up and shut down, effectively blocking system shutdown. This is a big problem on my pseudo-distributed instance on my laptop.
The init script default stops for HBase services should be set to something like:
K17hadoop-hbase-regionserver
K18hadoop-hbase-master
K19hadoop-zookeeper-server
K20hadoop-*