Em man sudoers sob o cabeçalho User Specification , diz:
The basic structure of a user specification is 'who = where (as_whom) what'.
Em Tag_Spec , diz:
NOPASSWD and PASSWD
By default, sudo requires that a user authenticate him or herself before running a command.
Usando visudo edite a linha %sudo ALL=(ALL:ALL) ALL para ler:
# Allow members of group sudo on any host as any user to execute any command without a password
%sudo ALL=(ALL:ALL) NOPASSWD: ALL