For the four phases of Oracle Database startup, see:
1. The database is in the SHUTDOWN status.
In this status, the database is stopped. External data requests cannot be accepted. You cannot use the operating system command ps-ef | grep ora to see the existence of any database process.
2. The database is in the NOMOUNT status.
In this status, the database background process has been created. Create a shared memory area and a default oracle Database process based on the SGA-related parameters in the parameter file. Check whether the initialization parameters are correct.
You can use the operating system command to test the corresponding process. Ps-ef | grep ora _ and use the ipcs-m command to view the shared memory zone created by oracle users.
Oracle @ db1: ~> Sqlplus/as sysdba
SQL * Plus: Release 10.2.0.1.0-Production on Sat Mar 3 22:48:27 2012
Copyright (c) 1982,200 5, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup nomount;
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 104859892 bytes
Database Buffers 58720256 bytes
Redo Buffers 2973696 bytes
SQL>
View the Process status.
Oracle @ db1: ~> Ps-ef | grep ora _
Oracle 3626 1 0? 00:00:00 ora_pmon_orcl1
Oracle 3628 1 0? 00:00:00 ora_psp0_orcl1
Oracle 3630 1 0? 00:00:00 ora_mman_orcl1
Oracle 3632 1 0? 00:00:00 ora_dbw0_orcl1
Oracle 3634 1 0? 00:00:00 ora_lgwr_orcl1
Oracle 3636 1 0? 00:00:00 ora_ckpt_orcl1
Oracle 3638 1 0? 00:00:00 ora_smon_orcl1
Oracle 3640 1 0? 00:00:00 ora_reco_orcl1
Oracle 3642 1 0? 00:00:00 ora_cjq0_orcl1
Oracle 3644 1 0? 00:00:00 ora_mmon_orcl1
Oracle 3646 1 0? 00:00:00 ora_mmnl_orcl1
Oracle 3648 1 0? 00:00:00 ora_d000_orcl1
Oracle 3650 1 0? 00:00:00 ora_s000_orcl1
Oracle 3669 3652 0 00:00:00 pts/2 grep ora _
Oracle @ db1: ~>
Oracle @ db1: ~> Ipcs-m
------ Shared Memory Segments --------
Key shmid owner perms bytes nattch status
0xe835086c 458764 oracle 640 171966464 14
Oracle @ db1: ~>