I installed Oracle 11gR2 on my linux server. When I want to login via sys user on my db, I enter "sys as sysdba" and when system give password , I push enter and I can login on my db with sqlplus.
But, when I try to connect on Windows with PL-SQL tool, system wants to password. If I didn't write password (I defined password, password is "sys"), I cannot login on my db.
Why?
When you connect on the same server you're being authenticated by the operating system; you can give any password you like, or it's more common to use / as sysdba.
When you connect from PL/SQL it'a a remote connection; operating system authentication isn't possible, so you're using password authentication.
When you install oracle, it creates OSDBA and OSOPER groups. Any members of this groups will have OS authentication and can logon without a password.
When you connect from another machine, it's a remote connection and you must enter the password.
More info in the documentation.
I had such a problem and even with Oracle 12c on my linux server and what i did was that each time I open a new terminal I first type
"export TWO_TASK="
(without the the quotations) followed by pressing
enter.
Next I could then go ahead to type sqlplus "/as sysdba" (now as it is with the quotations)
to connect and continue.
