Database startup (below), Database startup (

Database startup (below), Database startup (

3. STARTUP

This command completes the three steps of creating an instance, installing an instance, and opening a database. At this time, the database makes the data document and the re-log document online, and usually requests one or more rollback segments. In this case, the system can not only see the previous Startup
In addition to any prompts in the Mount mode, a "database opened" prompt is also displayed. In this case, the database system is in normal operation and can accept user requests.

If you use startup nomount or startup mount to open a command, you must use ALTER
DATABASE command to open the DATABASE. For example, if you use STARTUP
NOMOUNT mode to open the database, that is, the instance has been created, but the database is not installed and opened. The following two commands must be run to start the database correctly.

Alter database mount;

Alter database open;

If you start the database in the startup mount mode, you only need to run the following command to open the database:

Alter database open.

4. Other open methods

In addition to the three methods of opening the database, there are also some other options.

(1) STARTUP RESTRICT

In this way, the database is successfully opened, but only privileged users (users with DBA roles) are allowed to use the database. This method is often used to maintain the database. For example, you do not want other users to connect to the database for data import/export operations.

(2) STARTUP FORCE

This command is a combination of the two commands, shutdown abort and startup. This command is used only when the database is shut down and cannot be shut down.

(3) alter database open read only;

This command opens the database in read-only mode after creating an instance and installing the database. This method can be used to open product databases that only provide the query function.

In the three modes of the database, what files are opened for the database respectively?

It's you.
 
In linux, how does one start the oracle database? What is the command?

I use Redhat Linux and use the following steps to start the oracle database.
First, use the oracle user to log on to Linux, and then execute the following command in the shell command line:
Step 1: Enable Oracle listening
$ Lsnrctl start
Step 2: Go to sqlplus
$ Sqlplus/nolog
SQL>
Step 3: Use the sysdab role to log on to sqlplus
SQL> conn/as sysdba
Step 4: Start the database
SQL> startup
After the above four steps, the oracle database can be started.