建了一个新的测试库，启动监听时报了如下错误：
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
TNS-12547: TNS:lost contact
 TNS-12560: TNS:protocol adapter error
  TNS-00517: Lost contact
   Linux Error: 104: Connection reset by peer


   感觉是hostname所致，于是查询当前主机的hostname：
[oracle@o2o-T-DB ~]$ hostname
o2o-T-DB

   再查询hosts文件：
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1               o2o-T-DB
::1             localhost6.localdomain6 localhost6

   172.0.0.1是我手动改过的，怀疑和这里有关，于是又把默认值加回去：

# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1         localhost.localdomain   localhost
127.0.0.1               o2o-T-DB
::1             localhost6.localdomain6 localhost6

    再重新启动监听，成功了。看来修改hosts，除了添加新的hostname，默认数值也一定要保留。