SYS When any database is created, the user SYS is automatically created and granted the DBA role.All of the base tables and views for the database's data dictionary are stored in the schema SYS. These base tables and views are critical for the operation of Oracle. To maintain the integrity of the data dictionary, tables in the SYS schema are manipulated only by Oracle. They should never be modified by any user or database administrator, and no one should create any tables in the schema of user SYS. (However, you can change the storage parameters of the data dictionary settings if necessary.)Ensure that most database users are never able to connect using the SYS account.SYSTEM When a database is created, the user SYSTEM is also automatically created and granted the DBA role.The SYSTEM username is used to create additional tables and views that display administrative information, and internal tables and views used by various Oracle options and tools. Never create in the SYSTEM schema tables of interest to individual users
Database Administrator Usernames Two user accounts are automatically created with the database:SYS (default password: CHANGE_ON_INSTALL) SYSTEM (default password: MANAGER) -------------------------------------------------------------------------------- Note: Oracle recommends that you specify passwords for SYS and SYSTEM at database creation time, rather that using these default passwords. This is explained in "Protecting Your Database: Specifying Passwords for Users SYS and SYSTEM". If you use the default passwords, to prevent inappropriate access to the data dictionary tables or other tampering with the database, it is important that you change the passwords for the SYS and SYSTEM usernames immediately after creating an Oracle database.-------------------------------------------------------------------------------- It is suggested that you create at least one additional administrator user, and grant that user the DBA role, to use when performing daily administrative tasks. It is recommended that you do not use SYS and SYSTEM for these purposes. -------------------------------------------------------------------------------- Note Regarding Security Enhancements: In this release of Oracle and in subsequent releases, several enhancements are being made to ensure the security of default database user accounts.During initial installation with the Database Configuration Assistant (DCBA), all default database user accounts except SYS, SYSTEM, SCOTT, DBSNMP, OUTLN, AURORA$JIS$UTILITY$, AURORA$ORB$UNAUTHENTICATED and OSE$HTTP$ADMIN are locked and expired. To activate a locked account, the DBA must manually unlock it and reassign it a new password. In addition, the DBCA prompts for passwords for users SYS and SYSTEM during initial installation of the database rather than assigning default passwords to them. A CREATE DATABASE statement issued manually also lets you supply passwords for these two users.
那当然了。sys无所不能。sys可以启动数据库，关闭实例...dba不可以。
When any database is created, the user SYS is automatically created and granted the DBA role.All of the base tables and views for the database's data dictionary are stored in the schema SYS. These base tables and views are critical for the operation of Oracle. To maintain the integrity of the data dictionary, tables in the SYS schema are manipulated only by Oracle. They should never be modified by any user or database administrator, and no one should create any tables in the schema of user SYS. (However, you can change the storage parameters of the data dictionary settings if necessary.)Ensure that most database users are never able to connect using the SYS account.SYSTEM
When a database is created, the user SYSTEM is also automatically created and granted the DBA role.The SYSTEM username is used to create additional tables and views that display administrative information, and internal tables and views used by various Oracle options and tools. Never create in the SYSTEM schema tables of interest to individual users
Two user accounts are automatically created with the database:SYS (default password: CHANGE_ON_INSTALL)
SYSTEM (default password: MANAGER)
--------------------------------------------------------------------------------
Note:
Oracle recommends that you specify passwords for SYS and SYSTEM at database creation time, rather that using these default passwords. This is explained in "Protecting Your Database: Specifying Passwords for Users SYS and SYSTEM". If you use the default passwords, to prevent inappropriate access to the data dictionary tables or other tampering with the database, it is important that you change the passwords for the SYS and SYSTEM usernames immediately after creating an Oracle database.--------------------------------------------------------------------------------
It is suggested that you create at least one additional administrator user, and grant that user the DBA role, to use when performing daily administrative tasks. It is recommended that you do not use SYS and SYSTEM for these purposes.
--------------------------------------------------------------------------------
Note Regarding Security Enhancements:
In this release of Oracle and in subsequent releases, several enhancements are being made to ensure the security of default database user accounts.During initial installation with the Database Configuration Assistant (DCBA), all default database user accounts except SYS, SYSTEM, SCOTT, DBSNMP, OUTLN, AURORA$JIS$UTILITY$, AURORA$ORB$UNAUTHENTICATED and OSE$HTTP$ADMIN are locked and expired. To activate a locked account, the DBA must manually unlock it and reassign it a new password.
In addition, the DBCA prompts for passwords for users SYS and SYSTEM during initial installation of the database rather than assigning default passwords to them. A CREATE DATABASE statement issued manually also lets you supply passwords for these two users.