linux - RHEL - can't sudo from script -

i have script i'm trying change user (from root) on boot. in /etc/rc.d/rc.local, i've changed cd script dir , execute it. works except when tries execute:

sudo -u newuser ./myscript.sh 

i error message:

sorry, must have tty run sudo 

so went , looked in /etc/sudoers file, , set !requiretty, should turn off. have tried alternatives such gksudo, apparently rhel 6.5 supports basic sudo.

i know script works because can execute myself terminal, it's when try , execute boot script.

just changed:

sudo -u newuser ./myscript.sh 

to:

/bin/su -c ./myscript.sh newuser 

and seems work. guess because sudo there elevate privileges since starts root don't need , can use su instead. try out in various places make sure works 100%.