isc-dhcp-server.serviceを起動できません：単位isc-dhcp-server.serviceはマスクです。

以下は必須情報です。

root@usbarmory:/etc/dhcp# service isc-dhcp-server start
Failed to start isc-dhcp-server.service: Unit isc-dhcp-server.service is masked.

root@usbarmory:/etc/dhcp# cat dhcpd.conf 
ddns-update-style none;
option domain-name "domain.local";
option domain-name-servers 10.0.0.1;
default-lease-time 60;
max-lease-time 72;
authoritative;
log-facility local7;
option local-proxy-config code 252 = text;
subnet 10.0.0.0 netmask 255.255.255.0 {
option local-proxy-config "http://10.0.0.1/wpad.dat";
option routers 10.0.0.1
range 10.0.0.3 10.0.0.3;
}

root@usbarmory:/etc/dhcp# service isc-dhcp-server status
● isc-dhcp-server.service
   Loaded: masked (/dev/null)
   Active: inactive (dead)

usb0      Link encap:Ethernet  HWaddr 1a:55:89:a2:69:41  
          inet addr:10.0.0.1  Bcast:10.0.0.255  Mask:255.255.255.0
          inet6 addr: fe80::1855:89ff:fea2:6941/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3078 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1815 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:324336 (316.7 KiB)  TX bytes:316731 (309.

3KB）