it in the Windows download cmd, and use the command line to enter under the oracle user in Linux. Operating system authentication uses a password file for authentication, which is generated when the database is created, so you can log in without a password.
[root@localhost ~]# su - oracle
[oracle@localhost ~]$ sqlplus / as sysdba Search
SQL*Plus: Release 11.2.0.4.0 Production on Fri Jul 15 15:49:47 2016
Copyright (c) 1982, 2013 , Oracle. All rights reserved.
Use the "alter user user identified by password" command to change the password.
Replace "user" in the command with "sys" or "system" and replace "password" with the password that needs to be set.
SQL> alter user sys identified by oracle;
User altered.
SQL> alter user system identified by oracle;
User altered.
