From the command line (assuming you are logged in as linux oracle userid) the password field is ignored. I tried it on my 11g system logged onto Linux as my oracle user.
sqlplus sys/fred as sysdba << I connected.
sqlplus sys/wilma as sysdba << I connected.
Try to connect as sys without the /password so it prompts you for the pwd
sqlplus sys as sysdba << should prompt you for a password
<< now try your password to verify your sys password
from the command I usually just do ‘sqlplus / as sysdba’ to connect as sys.
I hope this helps.