ORA-01092: ORACLE instance terminated. Disconnection forced

I got ” ORA-01092: ORACLE instance terminated. Disconnection forced ”  error in Oracle database.

ORA-01092: ORACLE instance terminated. Disconnection forced

Details of error are as follows.

ORA-01092: ORACLE instance terminated. Disconnection forced
Cause: The instance connected to was terminated abnormally, probably due to a SHUTDOWN ABORT. 
The current process was forced to disconnect from the instance.

Action: Examine the alert log for more details. Contact the database administrator to determine 
when the instance is restarted. Attempt to reconnect after the instance is running again.

Database instance crashed with the following error in alert.log:

Wed Nov 02 06:23:51 2020
Non critical error ORA-00001 caught while writing to trace file "<PATH>/<SID>_arc1_2076702.trc"
Error message: IBM AIX RISC System/6000 Error: 5: I/O error
Additional information: 1
Writing to the above trace file iWed Nov 02 06:29:56 2020
USER (ospid: 643220): terminating the instance due to error 1092
Wed Nov 02 06:29:56 2020
ORA-1092 : opitsk aborting process
Instance terminated by USER, pid = 643220

ORACLE instance terminated. Disconnection forced

This ORA-01092 errors are related with the instance connected to was terminated abnormally, probably due to a SHUTDOWN ABORT.

The current process was forced to disconnect from the instance.

Examine the alert log for more details. Contact the database administrator to determine when the instance is restarted. Attempt to reconnect after the instance is running again.

Looking at entries in alert.log prior to crash, following is seen:

a. DBWR process experiencing I/O error:

b. Entries in alert.log is incomplete:

2. MMON process trace file shows:

Unix process pid: 1949800, image: oracle@xxx (MMON)
Taking over instance termination because the instance terminator (ospid: 2875438) is dead
===> 2875438 is the OS PID of DBW0 process which encountered the I/O error and is dead.

3. The instance was then terminated by USER process with the OS PID 643220.

Trace file for this process shows:

Taking over instance termination because the instance terminator (ospid: 2191470) is dead
kjzduptcctx: Notifying DIAG for crash event
----- Abridged Call Stack Trace -----
ksedsts()+644<-kjzdssdmp()+444<-kjzduptcctx()+272<-kjzdicrshnfy()+96<-ksuitm()+1284<-ksuitr()+92<-ksu_dispatch_tac()+372<-kdifxs1()+468<-kdifxs()+28<-qerixtFetch()+940
<-qerilFetch()+276<-opifch2()+7136<-opifch()+60<-opiodr()+3608<-rpidrus()+536<-skgmstack()+208
<-rpidru()+144<-rpiswu2()+1124<-rpidrv()+2892<-rpifch()+80
----- End of Abridged Call Stack Trace -----

USER (ospid: 643220): terminating the instance due to error 1092

5. OS logs (/var/log on AIX) reports I/O errors :


Description
USER DATA I/O ERROR

Probable Causes
ADAPTER HARDWARE OR MICROCODE
DISK DRIVE HARDWARE OR MICROCODE
SOFTWARE DEVICE DRIVER
STORAGE CABLE LOOSE, DEFECTIVE, OR UNTERMINATED

select file#, status, name from v$datafile where status not in ('SYSTEM', 'ONLINE');

To solve this error, Check if you have a good backup from which you can restore any  problematic data file.

1) First restore the problematic datafiles
2) Mount the database and ONLINE those datafiles

SQL> startup mount;
SQL> alter database datafile  file1#, .. , filen# online;

3) Recover the database

 SQL> recover database;

4) Open database

SQL > alter database open ;

I/O errors

Contact your System/Unix administrator and rectify the hardware problem causing I/O error.

Or second case’s solution is as follows.

Connect to each database and ensure the Snapshot controlfile name and location are unique and not duplicate of each other

OS> rman target /

RMAN>  show SNAPSHOT CONTROLFILE NAME;

Do you want to learn Oracle Database for Beginners, then read the following articles.

Oracle Tutorial | Oracle Database Tutorials for Beginners ( Junior Oracle DBA )