user1 want to be able to 'su' to a specific user, without a password to be entered.
$ sudo visudo
$ user1 ALL=(ALL) NOPASSWD: /bin/bash
for all users
$ user1 ALL=(ALL) NOPASSWD: ALL
user1 want to be able to 'su' to a specific user, without a password to be entered.
$ sudo visudo
$ user1 ALL=(ALL) NOPASSWD: /bin/bash
for all users
$ user1 ALL=(ALL) NOPASSWD: ALL