ORACLE12 - Connect Via SqlPlus I have a local installation of Oracle
Before i can connect directly via SqlPlus
but now when i try to connect i have this error :


  ERROR:
  ORA-01034: ORACLE not available
  ORA-27101: shared memory realm does not exist
  Linux-x86_64 Error: 2: No such file or directory
  Additional information: 3640
  Additional information: 684464879
  Process ID: 0
  Session ID: 0 Serial number: 0


Can you tell me what is the cause of this Error ?
how can i solve it ?
Make sure the database is actually running, and if not, start it. If you have an init script, then it's typically something like:

sudo service oracle start


This has been asked before for Oracle 11g - the answers and comments to that question may be helpful here:
ORA-01034: ORACLE not available in oracle 11g