Linux hostname对Oracle实例以及监听的影响

    在Linux平台中，对hostname的修改，是否对ORACLE数据库实例或监听进程有影响呢？如果有影响，又要如何解决问题呢？另外/etc/hosts下相关内容的修改，是否也会影响实例或监听呢？这里涉及的场景非常多，当然关系也非常复杂，我们下面通过几个例子来测试验证一下。

    如下所示，服务器/etc/hosts 与/etc/sysconfig/network的原始配置信息如下

[root@test ~]# more /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1            localhost6.localdomain6 localhost6

127.0.0.1       localhost.localdomain localhost

192.168.27.134  test test 

[root@test ~]# 

[root@test ~]# more /etc/sysconfig/network

.NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=test

GATEWAY=192.168.27.1

[root@test ~]# 

1： 首先假设有个需求，需要修改hostname，使之变成test.edution.com（加上域名部分）, 那么此时是否有问题呢？我们先修改/etc/sysconfig/network下的HOSTNAME，然后重启服务器

[root@test ~]# more  /etc/sysconfig/network

NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=test.eduction.com

GATEWAY=192.168.27.1

[root@test ~]# vi /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1            localhost6.localdomain6 localhost6

127.0.0.1       localhost.localdomain localhost

192.168.27.134  test test

然后我们重启数据库实例后，并没有任何问题，但是重启监听的时候遇到下面错误：

[oracle@test ~]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.5.0 - Production on Sat Jun 18 16:42:21 2016

Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.

Connected to an idle instance.

SQL> startup

ORACLE instance started.

Total System Global Area 1509949440 bytes

Fixed Size                  2096472 bytes

Variable Size            1392509608 bytes

Database Buffers           67108864 bytes

Redo Buffers               48234496 bytes

Database mounted.

Database opened.

SQL> exit

Disconnected from Oracle Database 10g Release 10.2.0.5.0 - 64bit Production

[oracle@test ~]$ lsnrctl start

LSNRCTL for Linux: Version 10.2.0.5.0 - Production on 18-JUN-2016 16:42:47

Copyright (c) 1991, 2010, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/10.2.0/db_1/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 10.2.0.5.0 - Production

Log messages written to /u01/app/oracle/product/10.2.0/db_1/network/log/listener.log

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=test.eduction.com)(PORT=1521)))

Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))

TNS-12535: TNS:operation timed out

 TNS-12560: TNS:protocol adapter error

  TNS-00505: Operation timed out

   Linux Error: 110: Connection timed out

[oracle@test ~]$ 

出现这个问题时，必须修改/etc/hosts下主机名的部分，使之与/etc/sysconfig/network下的HOSTNAME一致，上面错误就能解决。如下红色部分所示：

[root@test ~]# more /etc/sysconfig/network

NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=test.eduction.com

GATEWAY=192.168.27.1

[root@test ~]# more /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1 localhost6.localdomain6 localhost6

127.0.0.1 localhost.localdomain localhost

192.168.27.134 test.eduction.com test

[root@test ~]#

由于这里测试，我修改了域名，如果服务器真实域名部分跟/etc/resolv.conf一致，那么数据库实例启动过程中，监控告警日志，就会发现告警日志里面会出现大量ORA-07445 & ORA-00108错误

2：修改/etc/sysconfig/network下的hostname并使之生效，如下所示

[oracle@kerry ~]$ more /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1            localhost6.localdomain6 localhost6

127.0.0.1       localhost.localdomain localhost

192.168.27.134  test.eduction.com  test 

[oracle@kerry ~]$ more /etc/sysconfig/network

NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=kerry.eduction.com

GATEWAY=192.168.27.1

数据库实例启动并没有任何问题，但是监听启动出现上面一样的错误。 如果域名使用真实的域名，则会遇到另外一种情况，告警日志里面也会出现下面错误

Errors in file /u01/app/oracle/admin/SCM2/bdump/scm2_ora_4494.trc:

ORA-07445: exception encountered: core dump [kslgetl()+120] [SIGSEGV] [Address not mapped to object] [0x000000210] [] []

ORA-00108: failed to set up dispatcher to accept connection asynchronously

关于这个，可以参考官方文档ORA-07445: [kslgetl()+80] Followed by ORA-108: failed to set up dispatcher to accept connection asynchronously (文档 ID 1298804.1)

3： 如果屏蔽/etc/hosts下的localhost部分，如下所示，此时有可能会影响监听

[root@kerry ~]# more /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1            localhost6.localdomain6 localhost6

#127.0.0.1       localhost.localdomain localhost

192.168.27.134  kerry.eduction.com  kerry 

[root@kerry ~]# 

[oracle@kerry ~]$ lsnrctl start

LSNRCTL for Linux: Version 10.2.0.5.0 - Production on 18-JUN-2016 17:45:37

Copyright (c) 1991, 2010, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/10.2.0/db_1/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 10.2.0.5.0 - Production

Log messages written to /u01/app/oracle/product/10.2.0/db_1/network/log/listener.log

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=kerry.eduction.com)(PORT=1521)))

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

这是因为我没有在$ORACLE_HOME/network/admin下配置listener.ora,所以在注释或删除了/etc/hosts下localhost部分后就会出现这个错误，因为在没有listener.ora下的情况下，都会使用默认值（如下官方文档描述），监听进程会使用本机配置127.0.0.1注册监听服务,所以会出现上面错误信息，官方文档关于这方面的描述如下所示：

Oracle Net Listener Configuration Overview

Note:

Oracle Database 10g and later databases require a version 10 or later listener. Earlier versions of the listener are not supported for use with Oracle Database 10g and later databases. However, you can use a version 10 listener with previous versions of Oracle Database.

A listener is configured with one or more listening protocol addresses, information about supported services, and parameters that control its runtime behavior. The listener configuration is stored in a configuration file named listener.ora.

Because all of the configuration parameters have default values, it is possible to start and use a listener with no configuration. This default listener has a name of LISTENER, supports no services on startup, and listens on the following TCP/IP protocol address:

(ADDRESS=(PROTOCOL=tcp)(HOST=host_name)(PORT=1521))

Supported services, that is, the services to which the listener forwards client requests, can be configured in the listener.ora file or this information can be dynamically registered with the listener. This dynamic registration feature is called service registration. The registration is performed by the PMON process—an instance background process—of each database instance that has the necessary configuration in the database initialization parameter file. Dynamic service registration does not require any configuration in the listener.ora file.

解决方案两种：

1：在$ORACLE_HOME/network/admin/下配置listener.ora文件。则屏蔽或删除/etc/hosts下127.0.0.1后，监听不会有任何问题。

2：在配置文件/etc/hosts下增加localhost（红色部分所示）也能解决这个问题。

[root@kerry ~]# more /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

#::1 localhost6.localdomain6 localhost6

#127.0.0.1 localhost.localdomain localhost

192.168.27.134 kerry.eduction.com kerry localhost

[root@kerry ~]#

具体可以参考官方文档Starting TNS Listener or LSNRCTL Start Yields TNS-12541, Linux Error: 111: Connection Refused (文档 ID 343295.1)

  另外，我们这里也忽略了lisnter.ora里面的配置，如果该配置文件使用的是hostname而不是IP，那么也会遇到一些问题。

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原标题：Linux hostname对Oracle实例以及监听的影响

关键词：linux