[sudo-users] Error: sudo: no tty present and no askpass program specified

[Todd C. Miller]

Recent versions of sudo will refuse to prompt for a password if no
tty is present, since it is not possible to turn off echo in this
case.  You can restore the old behavior with a line like:

Defaults visiblepw

in sudoers.  However, since you have X windows available you could
use a graphical prompter instead.  Sudo doesn't come with its own
but it is possible to use the ssh one.  To do this, either set
the SUDO_ASKPASS environment variable or the "askpass" setting
in sudoers to something like /usr/libexec/openssh/ssh-askpass.

 - todd