I have been attempting to use 'Terminal' in Ubuntu 17.4 ( I think that is the right version ) to configure a printer.but when I try to use 'sudo system-config-printer' then on the next line '[sudo] password for edward' with a small white vertical rectangle immediately following appears. I have tried to enter my password at this point, but cannot enter anything there. I can't go back to the previous line to try entering it there either. I can't find anywhere to actually enter anything !

Please tell me where and how to enter the password. I had last successfully used 'Terminal' on a different 'Ubuntu' computer about a year ago but the way to enter the password for 'sudo' seems to have changed since then.

I have looked at the manual page for 'sudo' but it did not help that below the last visible line there was an obscuring message on white background and I could not shift this to see whether the manual page continued beneath it with the required information.

so you mean there is no space to enter your password?
I think you can still enter your password and should be accepted (even when you can't see anything).
Would be nice to show us a screenshot or explain better what's happening.

1 members found this post helpful.

Just a note that you shouldn't still be using Ubuntu 17.04 - it went end-of-life on 13 Jan 2018.

You should upgrade to the short-term version 17.10, wait for the long-term version 18.04 next month, or downgrade to the long-term version 16.04.

the password is not echoed even as * for security purpose, try entering the password and hitting enter and see if it does anything

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+1 for the screenshot. It could make a big difference in diagnosing the problem.

In the unix/linux world, when no GUI was involved this is the normal/expected behavior.
If there was a GUI (to ask password) usually dots are displayed (in windows stars), but sudo does not use GUI.
You may try gksudo system-config-printer too, that should display a dialog to enter the password.

1 members found this post helpful.

I thought Ubuntu installed passwordless sudo by default.

superannuated, in addition to what the others said:
you can enter Ctrl-c to abort a command.
you can navigate man pages with your arrow keys, or PgUp/PgDn.

General rule for displaying passwords:

* Graphical apps display an asterisk for each character you enter in the box.
* Command line displays nothing! It looks as if the keyboard has gone dead.

Don't panic! Just enter your password and press ENTER. It will be received.