Comment 6 for bug 1332544

For interest I have run into this on Ubuntu 14.04.
dnsmasq is run as user 'nobody', and gets
stat("/var/lib/neutron/dhcp/e2a6a633-45f4-4fcd-a842-0c5fb54b2fba/host", 0x7fff42977110) = -1 EACCES (Permission denied)

which silently fails (e.g. dnsmasq comes up but doesn't work) as it is invoked as:

dnsmasq --no-hosts --no-resolv --strict-order --bind-interfaces --interface=tapef46bd92-2c --except-interface=lo --pid-file=/var/lib/neutron/dhcp/e2a6a633-45f4-4fcd-a842-0c5fb54b2fba/pid --dhcp-hostsfile=/var/lib/neutron/dhcp/e2a6a633-45f4-4fcd-a842-0c5fb54b2fba/host --addn-hosts=/var/lib/neutron/dhcp/e2a6a633-45f4-4fcd-a842-0c5fb54b2fba/addn_hosts --dhcp-optsfile=/var/lib/neutron/dhcp/e2a6a633-45f4-4fcd-a842-0c5fb54b2fba/opts --leasefile-ro --dhcp-range=set:tag0,172.16.1.0,static,86400s --dhcp-lease-max=256 --conf-file=/etc/neutron/dnsmasq.conf --server=107.150.57.202 --domain=stack

changing /etc/neutron/dnsmasq.conf to add 'user=neutron' causes it to work properly.