我做了个实验，破环了在线当前日志组，实例崩溃。我在网上查了半天，最后决定先退出sqlplus环境再重新启动sqlplus。结果问题解决了。
SQL> startup
ORA-24324: service handle not initialized
ORA-01041: internal error. hostdef extension doesn't exist
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
[oracle@cuiyan ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Apr 24 14:58:20 2015
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup mount
ORACLE instance started.
Total System Global Area 608174080 bytes
Fixed Size 1220844 bytes
Variable Size 201330452 bytes
Database Buffers 402653184 bytes
Redo Buffers 2969600 bytes
Database mounted.
SQL> recover database until cancel;
ORA-00279: change 488525 generated at 04/24/2015 12:58:35 needed for thread 1
ORA-00289: suggestion : /home/oracle/arch/1_1_877869001.dbf
ORA-00280: change 488525 for thread 1 is in sequence #1
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
Media recovery cancelled.
SQL> alter database open resetlogs;
Database altered.