Depending on the platform and core release the login credentials are different. Normally, we limit controller shell access to support personnel and troubleshooting purposes only.
I cannot share the password directly here, but if you open a support case they can help you login and complete the necessary steps in the shell. The login user for most platforms is shellUsr.
For 2800 and 5700 platforms running SANtricity OS 11.40.2 or later (8.42.xx.xx), the password for the controller shell is the same as the admin user login password to SANtricity System Manager. And the login users are eos and diag. diag will log you into the Linux shell of the controller, while eos user will log you into the E-Series firmware shell.
If you plan to run any commands in the controller shell, I would advise to consult with NetApp support first to make sure the command would not cause any harm to the controller operation.
I don't know how ESERIES Controller works, but I suppose in general any new Filer(ESERIES) setup will not prompt you for the password, it will just let you in for setting it up. However, if this Appliance was already in use that means it has been setup & configured previously, in that case you must have 'password' to login (There is no default here).
I found one kb related to ESERIES, I suggest log a call/ticket with support for further course of action.