ORA-27101: shared memory realm does not exist

I am using Ubuntu 14.04 with Oracle 11g. But, it is not working properly. Given the below commands and output:

root@madhu-Lenovo-G500:~# sqlplus
SQL*Plus: Release 11.2.0.2.0 Production on Wed Jun 25 08:51:11 2014
Copyright (c) 1982, 2011, Oracle. All rights reserved.
Enter user-name: system/root
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0

2 Answers

Although the method I'm about to explain requires (at least on my system) the /etc/init.d/oracle-xe to be executed every time Ubuntu is started:

If you've followed the Oracle 11g installation instruction straight, try this out:

rm -rf /dev/shm
mkdir /dev/shm
mount -t tmpfs shmfs -o size=2048m /dev/shm

Note: The amount of memory defined for the "size" attribute will depend on how much memory the system has available, of course, and, if you're running under 32bits OS, the specified value is the maximum allowed, otherwise (64bits) you'll be able to set a greater value than that.

As I mentioned at the beginning, would be better if you insert the code shown here within /etc/init.d/oracle-xe like this:

if [ -L /dev/shm ]; then rm -rf /dev/shm mkdir /dev/shm mount -t tmpfs shmfs -o size=2048m /dev/shm
fi

Best regards.

sqlplus / as sysdba then issue command startup; to start the database

Also on Linux with this error, you can check first if Oracle background processes are up with ps aux | grep pmon. Pmon is process monitor, or check some other background process. If they are not running then the database is not running.