启动数据库：
pg_ctl start -D $PGDATA

关闭数据库：
pg_ctl stop -D $PGDATA [-m mode]

mode有三种模式：

	1. smart ：等待所有的连接终止后，关闭数据库。如果客户端连接不终止，则无法关闭数据库。看起来是Oracle的normal。
	2. fast：快速关闭数据库，断开客户端的连接，让已有的事务回滚，然后正常关闭数据库，看起来是Oracle的immediate。
	3. immediate：立即关闭数据库，相当于数据库进程立即停止，直接退出，下次启动数据库需要回复。看起来是Oracle的abort。


[postgres@single ~]$ pg_ctl start -D $PGDATA
server starting
[postgres@single ~]$ LOG: could not bind IPv6 socket: Address already in use
HINT: Is another postmaster already running on port 5432? If not,wait a few seconds and retry.
LOG: could not bind IPv4 socket: Address already in use
HINT: Is another postmaster already running on port 5432? If not,wait a few seconds and retry.
WARNING: could not create listen socket for "localhost"
FATAL: could not create any TCP/IP sockets
LOG: database system is shut down


发现是因为前面已经启动了-D /usr/pg/postgresql-9.6.1/data/
先停掉：
[postgres@single ~]$ pg_ctl stop -D /usr/pg/postgresql-9.6.1/data/
waiting for server to shut down.... done
server stopped

然后起：
[postgres@single ~]$ pg_ctl start -D $PGDATA
server starting
[postgres@single ~]$ LOG: database system was shut down at 2016-11-17 08:55:51 CST
LOG: MultiXact member wraparound protections are now enabled
LOG: database system is ready to accept connections
LOG: autovacuum launcher started

可以了。