Setup: ISC dhcpd

Ubuntu uses AppArmor to restrict certain programs' actions. The isc-dhcp-server package provides an AppArmor configuration file that only allows dhcpd to see and modify configuration files and logs in certain default locations. The simplest way to fix this is to give it read permissions on all files:

1. Edit the file /etc/apparmor.d/usr.sbin.dhcpd so that the /usr/sbin/dhcpd { ... } block includes the line /** r,
2. Restart the AppArmor service by running service apparmor restart as root