Startup Fails With ORA-01012: Not Logged On

Problem Description:-

User will not be able to get login to database. but sysdba is able to connect (Sometime it shows :-database connected to an idle instance), but he will not be able to run any query. But when we fire Startup, It will throw error ORA-01081: cannot start already-running ORACLE - shut it down first.

$sqlplus / as sysdba

SQL> select name,open_mode from v$database;
ERROR at line 1:
ORA-01012: not logged on

SQL> desc v$instance
ERROR:
ORA-01012: not logged on

SQL> startup
ORA-01012: not logged on

CAUSE 

An orphaned shared memory segment belonging to the ORACLE_SID still exists from a previous instance startup.

The command
ps -ef | grep $ORACLE_SID

shows no processes but with ORACLE_SID set the Oracle 'sysresv' utility shows a shared memory segment for a non-existing instance, e.g.

$sysresv

IPC Resources for ORACLE_SID "ABC" :Shared Memory:

ID              KEY

721420334       0x00000000

721420335       0x00000000

721420336       0x5b823e4c

Semaphores:

ID              KEY

50331757        0x9aa67508

Solution
On OS level, remove the orphaned shared memory segment using:

ipcrm -m <problem shared memory id>

$ ipcrm -m 721420334
$ ipcrm -m 721420335
$ ipcrm -m 721420336

$sqlplus '/as sysdba'

Connected to an idle instance.

SQL> startup
Total System Global Area   10689474560 bytes
Fixed Size                     2237776 bytes
Variable Size               6375344816 bytes
Database Buffers            4294967296 bytes
Redo Buffers                  16924672 bytes
Oracle Instance Started.
Oracle Database Opened.

NOTE:---in my case below is remaining issue

  So 

SQL> alter database end backup;

Database altered.

SQL> select name,open_mode from v$database;

NAME      OPEN_MODE

--------- --------------------

ABC       MOUNTED

SQL> alter database open;

Database altered.

SQL> select name,open_mode from v$database;

NAME      OPEN_MODE

--------- --------------------

ABC       READ WRITE

Startu Fails With ORA-01012: Not Logged On

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