到处一张表的时候报错        
[oracle@node1 ~]$ exp scott/oracle tables=emp5 file=/home/oracle/emp5.dbf
Export: Release 11.2.0.1.0 - Production on Sun Nov 17 16:59:32 2013

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, Data Mining and Real Application Testing options
Export done in US7ASCII character set and AL16UTF16 NCHAR character set
server uses ZHS16GBK character set (possible charset conversion)

About to export specified tables via Conventional Path ...
. . exporting table                           EMP5         14 rows exported
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
Export terminated successfully with warnings.

可能是字符的问题 
查看数据库的字符                            
SQL> select * from nls_database_parameters t where t.parameter='NLS_CHARACTERSET';   
PARAMETER
------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_CHARACTERSET
ZHS16GBK
[oracle@node1 ~]$ vi .bash_profile
export NLS_LANG=american_america.ZHS16GBK
[oracle@node1 ~]$ source .bash_profile

再次到处表，成功导出                      
[oracle@node1 ~]$ exp scott/oracle tables=emp5 file=/home/oracle/emp5.dbf
Export: Release 11.2.0.1.0 - Production on Sun Nov 17 17:20:45 2013
Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, Data Mining and Real Application Testing options
Export done in ZHS16GBK character set and AL16UTF16 NCHAR character set
About to export specified tables via Conventional Path ...
. . exporting table                           EMP5         14 rows exported
Export terminated successfully without warnings.