ORA-27101: shared memory realm does not exist
Check if the Oracle instance is running using the following command:
[oracle@dbdocs ~]$ ps -ef | grep pmon oracle 2572 1 0 04:36 ? 00:00:04 ora_pmon_dbdocs oracle 6105 2514 0 09:42 pts/0 00:00:00 grep --color=auto pmon [oracle@dbdocs ~]$
In the above example dbdocs oracle instance is up and running
dbdocs
If the instance is not running, start it using SQL*Plus:
$ sqlplus / as sysdba SQL> STARTUP;
Ensure that the ORACLE_SID environment variable is set correctly:
[oracle@dbdocs ~]$ echo $ORACLE_SID dbdocs [oracle@dbdocs ~]$
If it is not set correctly, set it using the following command:
$ export ORACLE_SID=your_sid
Check the shared memory segment settings on your operating system:
[oracle@dbdocs ~]$ ipcs -m ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x0000020e 0 postgres 600 56 6 0x00000000 3 oracle 600 9691136 134 0x00000000 4 oracle 600 2348810240 67 0x00000000 5 oracle 600 7086080 67 0x20897588 6 oracle 600 28672 67
If there are issues with shared memory segments, you may need to adjust your operating system's shared memory parameters.
Check the initialization parameters in your parameter file (pfile or spfile). Ensure all necessary parameters are set correctly. For example:
$ sqlplus / as sysdba SQL> SHOW PARAMETER db_cache_size; SQL> SHOW PARAMETER shared_pool_size;
If any parameters are missing or incorrect, modify them accordingly.
You attempt to connect to the database and receive the ORA-27101 error. Checking the process list shows that the Oracle instance is not running:
[oracle@dbdocs ~]$ ps -ef | grep pmon oracle 6154 2514 0 09:46 pts/0 00:00:00 grep --color=auto pmon [oracle@dbdocs ~]$
Solution: Start the Oracle instance:
$ sqlplus / as sysdba SQL> STARTUP; ORACLE instance started. Total System Global Area 2365585232 bytes Fixed Size 9688912 bytes Variable Size 822083584 bytes Database Buffers 1526726656 bytes Redo Buffers 7086080 bytes Database mounted. Database opened. SQL>
You receive the ORA-27101 error due to an incorrect ORACLE_SID environment variable:
$ echo $ORACLE_SID old_sid
Solution: Set the correct ORACLE_SID:
$ export ORACLE_SID=new_sid
The ORA-27101 error occurs due to insufficient shared memory allocation. Check the shared memory settings:
$ ipcs -m
Solution: Adjust the shared memory settings in your operating system configuration files (e.g., /etc/sysctl.conf) and reload the settings:
$ sysctl -p
ORA-27101: Shared Memory Realm Does Not Exist