Oracle – Startup Phases

There are 5 states an Oracle database goes through during the startup process.

1.  Shutdown
   The database is shutdown and cannot be connected to by anyone but SYS.
2. Startup nomount
   During this phase the database reads the initialization parameters from the spfile or pfile. If you get an error at this stage, it’s best to check this file exists, is accessible and contains no errors.
   This phase does not allow access to the database and is usually only done for database creation, or recreation of control files.
3. Startup mount
   During this phase the database checks the control file, this is a small binary file that records the physical structure of the database.
   If you receive errors during the mount phase, then it is best to check the control file exists.
   This phase allows for certain DBA activities to take place, but does not allow general access to the database.
4. Startup open
   During this phase the database tries to start in open mode, ready for all users to access. It checks the datafiles exist and any errors at this stage you should check the datafiles.
   This phase can be run in restricted or unrestricted mode, depending on whether you want all users to have access or not.