遇到网友咨询，类似故障重现:Liunx平台ORACLE数据库运行正常，ORACLE_SID正确，但是本地登录提示idle instance，tns方式可以正常登录现象
[oracle@xifenfei ~]$ ps -ef|grep pmon oracle 26295 1 0 04:11 ? 00:00:01 ora_pmon_XFF oracle 27997 27966 0 05:48 pts/0 00:00:00 grep pmon [oracle@xifenfei ~]$ env|grep ORA ORACLE_SID=XFF ORACLE_BASE=/u01/oracle ORACLE_HOME=/u01/oracle/oracle/product/10.2.0/db_1 [oracle@xifenfei ~]$ sqlplus / as sysdba SQL*Plus: Release 10.2.0.4.0 - Production on Sat Apr 20 05:48:30 2013 Copyright (c) 1982, 2007, Oracle. All Rights Reserved. Connected to an idle instance. SQL> [oracle@xifenfei ~]$ sqlplus sys/xifenfei@XFF as sysdba SQL*Plus: Release 10.2.0.4.0 - Production on Sat Apr 20 05:54:49 2013 Copyright (c) 1982, 2007, Oracle. All Rights Reserved. Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Production With the Partitioning, OLAP, Data Mining and Real Application Testing options SQL>
对于这样的现象，通过试验重现，并且通过oradebug ipc进行说明。
补充知识点:oracle本地认证是通过ipc进行的，而ipc是直接访问共享内存段的
系统当前状态
系统未启动然后数据库情况
[oracle@xifenfei ~]$ ipcs -m ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status [oracle@xifenfei ~]$ ps -ef|grep pmon|grep -v grep [oracle@xifenfei ~]$
启动数据库
确定环境变量ORACLE_SID,ORACLE_HOME
[oracle@xifenfei ~]$ env|grep ORA
ORACLE_SID=XFF
ORACLE_BASE=/u01/oracle
ORACLE_HOME=/u01/oracle/oracle/product/10.2.0/db_1
[oracle@xifenfei ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Sat Apr 20 04:10:22 2013
Copyright (c) 1982, 2007, Oracle. All Rights Reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 260046848 bytes
Fixed Size 1266896 bytes
Variable Size 83888944 bytes
Database Buffers 167772160 bytes
Redo Buffers 7118848 bytes
Database mounted.
Database opened.
--做debug ipc
SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.
SQL> oradebug tracefile_name
/u01/oracle/admin/XFF/udump/xff_ora_26852.trc
*** SESSION ID:(152.25) 2013-04-20 04:43:00.983
Dump of unix-generic skgm context
areaflags 000000e7
realmflags 0000000f
mapsize 00000800
protectsize 00001000
lcmsize 00001000
seglen 00200000
largestsize 00000000ffffffff
smallestsize 0000000000400000
stacklimit 0xbdb87e6c
stackdir -1
mode 640
magic acc01ade
Handle: 0xe781de0 `/u01/oracle/oracle/product/10.2.0/db_1XFF' --->注意($ORACLE_HOME$ORACLE_SID)
Dump of unix-generic realm handle `/u01/oracle/oracle/product/10.2.0/db_1XFF', flags = 00000000
Area #0 `Fixed Size' containing Subareas 0-0
Total size 00000000001354d0 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr --->主要Shmid
0 0 3080192 0x00000020000000 0x00000020000000
Subarea size Segment size
0000000000136000 000000000fa00000
Area #1 `Variable Size' containing Subareas 2-2
Total size 000000000f000000 Minimum Subarea size 00400000
Area Subarea Shmid Stable Addr Actual Addr
1 2 3080192 0x00000020800000 0x00000020800000
Subarea size Segment size
000000000f000000 000000000fa00000
Area #2 `Redo Buffers' containing Subareas 1-1
Total size 00000000006ca000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
Area Subarea Shmid Stable Addr Actual Addr
[oracle@xifenfei ~]$ ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x6fd58208 3080192 oracle 640 262144000 17
这里证明ipc的处理是通过$ORACLE_HOME$ORACLE_SID进行的,修改ORACLE_HOME，进一步验证
修改ORACLE_HOME
[oracle@xifenfei ~]$ export ORACLE_HOME=/u01/oracle/oracle/product/10.2.0/db_1/ [oracle@xifenfei ~]$ env|grep ORA ORACLE_SID=XFF ORACLE_BASE=/u01/oracle ORACLE_HOME=/u01/oracle/oracle/product/10.2.0/db_1/ [oracle@xifenfei ~]$ sqlplus / as sysdba SQL*Plus: Release 10.2.0.4.0 - Production on Sat Apr 20 04:11:46 2013 Copyright (c) 1982, 2007, Oracle. All Rights Reserved. Connected to an idle instance. SQL> startup ORACLE instance started. Total System Global Area 260046848 bytes Fixed Size 1266896 bytes Variable Size 83888944 bytes Database Buffers 167772160 bytes Redo Buffers 7118848 bytes ORA-01102: cannot mount database in EXCLUSIVE mode [oracle@xifenfei ~]$ ipcs -m ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x6fd58208 3080192 oracle 640 262144000 18 0x079d1b38 3112964 oracle 640 262144000 13 --启动两个同样的sid实例 [oracle@xifenfei ~]$ ps -ef|grep pmon|grep -v grep oracle 26211 1 0 04:10 ? 00:00:00 ora_pmon_XFF oracle 26295 1 0 04:11 ? 00:00:00 ora_pmon_XFF SQL> oradebug setmypid Statement processed. SQL> oradebug ipc Information written to trace file. SQL> oradebug tracefile_name /u01/oracle/admin/XFF/udump/xff_ora_27708.trc *** SESSION ID:(159.5) 2013-04-20 05:32:00.969 Dump of unix-generic skgm context areaflags 000000e7 realmflags 0000000f mapsize 00000800 protectsize 00001000 lcmsize 00001000 seglen 00200000 largestsize 00000000ffffffff smallestsize 0000000000400000 stacklimit 0xbdb5979c stackdir -1 mode 640 magic acc01ade Handle: 0xd99ede0 `/u01/oracle/oracle/product/10.2.0/db_1/XFF'--->注意 Dump of unix-generic realm handle `/u01/oracle/oracle/product/10.2.0/db_1/XFF', flags = 00000000
进一步证明在linux/unix系统，oracle数据库的内存段是通过ORACLE_HOME和ORACLE_SID结合起来识别的,只要ORACLE_HOME或者ORACLE_SID不一样就不能通过IPC访问实例的内存段,也就不能登录数据库
