dev ttyS0 linux how apt adjust the permissions

In redhat el5 ,GHD Purple Butterfly 2011, the way to reg code wharf ttyS0,GHD Green Straighteners, forever reported permisson denied,GHD Straighteners NZ, that / dev/ttyS0 the file permissions are 0660 ,GHD MK4 Gold Straighteners, 0666 tin be modified ,GHD Straighteners, merely the system ambition automatically restart and then into 0660 ,GHD Hair Straightener, where to change?

google an answer :

/ etc/udev/rules.d/50-udev.rules

26 KERNEL ==