注释掉/etc/hosts中127.0.0.1一行，启动oracle侦听程序可能报错，如下：

[root@n2 ~]# su - oracle
[oracle@n2 ~]$ lsnrctl start


LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 25-MAY-2016 09:42:25


Copyright (c) 1991, 2013, Oracle.  All rights reserved.


Starting /oracle/db/ora11g/bin/tnslsnr: please wait...


TNS-12537: TNS:connection closed
 TNS-12560: TNS:protocol adapter error
  TNS-00507: Connection closed
   Linux Error: 29: Illegal seek
[oracle@n2 ~]$ cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
#127.0.0.1      localhost


192.168.56.201 n1
192.168.56.202 n2
10.0.3.201     n1
10.0.3.202     n2
[oracle@n2 ~]$ exit
logout


[root@n2 ~]# vi /etc/hosts
[root@n2 ~]# su - oracle
[oracle@n2 ~]$ cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1      localhost


192.168.56.201 n1
192.168.56.202 n2
10.0.3.201     n1
10.0.3.202     n2
[oracle@n2 ~]$ lsnrctl start


LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 25-MAY-2016 09:43:33


Copyright (c) 1991, 2013, Oracle.  All rights reserved.


Starting /oracle/db/ora11g/bin/tnslsnr: please wait...


TNSLSNR for Linux: Version 11.2.0.4.0 - Production
System parameter file is /oracle/db/ora11g/network/admin/listener.ora
Log messages written to /oracle/db/diag/tnslsnr/n2/listener/alert/log.xml
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=n2)(PORT=1521)))


Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=n2)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 11.2.0.4.0 - Production
Start Date                25-MAY-2016 09:43:33
Uptime                    0 days 0 hr. 0 min. 0 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /oracle/db/ora11g/network/admin/listener.ora
Listener Log File         /oracle/db/diag/tnslsnr/n2/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=n2)(PORT=1521)))
Services Summary...
Service "dg2" has 1 instance(s).
  Instance "dg2", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully
[oracle@n2 ~]$