解决ORA-21561
在linux上使用sqlplus连接oracle数据库

[root@china ~]# sqlplus test/test@ORCL
SQL*Plus: Release 11.2.0.3.0 Production on Thu May 31 11:06:15 2018
Copyright (c) 1982, 2011, Oracle.  All rights reserved.

ERROR:
ORA-21561: OID generation failed

解决过程
在终端上输入：~ hostname
china
查看/etc/hosts文件：~ cat /etc/hosts
127.0.0.1 localhost
保持hostname与hosts文件中127.0.0.1对应的名称一致即可！

[root@china ~]# cat /etc/hosts
127.0.0.1   china
::1         localhost localhost.localdomain localhost6