creating a linux user that can do "reboot" command only without sudo
Solution 1:
This can be done quite simply using /usr/sbin/visudo to add the following lines:
User_Alias REBOOTUSERS = Lee, testuser
REBOOTUSERS ALL = NOPASSWD : reboot
After adding those lines the user(s) specified by the User_Alias REBOOTUSERS will be able to enter:
$sudo reboot
And it will reboot the server without a password prompt!
Solution 2:
Just use the NOPASSWD option in your sudoers config for that user/command.