standby shutdown

I need to do OS maintenance on a system running a standby in recovery
using pg_standby. I've gotten mixed results with doing the stop/start
with pg_ctl. Sometimes the standby is not recoverable. What should
the shutdown script look like if the standby is to be usable on the
other side? The log seems to indicate that interuption of recovery
is bad. What should the script look for to avoid that?

"-m i" left it in this state:

2009-05-01 00:42:15 EDT,0, LOG: database system was interrupted while in recovery at log time 2009-05-01 00:34:06 EDT
2009-05-01 00:42:15 EDT,0, HINT: If this has occurred more than once some data might be corrupted and you might need to choose an earlier recovery target.
2009-05-01 00:42:15 EDT,0, LOG: could not open file "pg_xlog/00000001000000000000000A" (log file 0, segment 10): No such file or directory
2009-05-01 00:42:15 EDT,0, LOG: invalid primary checkpoint record
2009-05-01 00:42:15 EDT,0, LOG: could not open file "pg_xlog/000000010000000000000009" (log file 0, segment 9): No such file or directory
2009-05-01 00:42:15 EDT,0, LOG: invalid secondary checkpoint record
2009-05-01 00:42:15 EDT,0, PANIC: could not locate a valid checkpoint record
2009-05-01 00:42:14 EDT,0, LOG: startup process (PID 25121) was terminated by signal 6: Aborted
2009-05-01 00:42:14 EDT,0, LOG: aborting startup due to startup process failure