Overwrites /etc/resolv.conf on every boot

1) You shouldn't manually update your resolv.conf, because all changes will be overwritten by data that your local DHCP server provides. If you want it to be static, run sudo dpkg-reconfigure resolvconf and answer "no" to dynamic updates. If you want to add new entries there, edit /etc/resolvconf/resolv.conf.d/base and run sudo resolvconf -u, it will append your entries and DHCP server's entries.

2) Try to edit your /etc/network/interfaces and add your entries there, like

auto eth0 
iface eth0 inet dhcp 
dns-search google.com 
dns-nameservers dnsserverip 

and then restart /etc/init.d/networking restart or sudo ifdown -a and sudo ifup -a

3) Your system uses udhcp which is a very small DHCP client program. The udhcp client negotiates a lease with the DHCP server and notifies a set of scripts when a leases is obtained or lost. You can read about it's usage here or just edit this script (as you did).

Source