dhcpd.pid file is different in /etc/init/ and /etc/init.d

[atimonin]

in /etc/init/isc-dhcp-server.conf (near end of file)

exec dhcpd -user dhcpd -group dhcpd -f -q -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES

in /etc/init.d/isc-dhcp-server

# try to read pid file name from config file, with fallback to /var/run/dhcpd.pid
if [ -z "$DHCPD_PID" ]; then
        DHCPD_PID=$(sed -n -e 's/^[ \t]*pid-file-name[ \t]*"(.*)"[ \t]*;.*$/\1/p' < "$DHCPD_CONF" 2>/dev/null | head -n 1)
fi
DHCPD_PID="${DHCPD_PID:-/var/run/dhcpd.pid}"

The default dhcpd.pid file location differ (should be same).

So if you'll try to do:
/etc/init.d/isc-dhcp-server restart
you'll get TWO dhcpd servers!

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: upstart 1.10-0ubuntu7
ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
Uname: Linux 3.11.0-12-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Wed Jan 29 22:05:38 2014
InstallationDate: Installed on 2014-01-09 (20 days ago)
InstallationMedia: Ubuntu-Server 13.10 "Saucy Salamander" - Release amd64 (20131016)
MarkForUpload: True
ProcKernelCmdline: BOOT_IMAGE=/vmlinuz-3.11.0-12-generic root=/dev/mapper/spb--office--vg-root ro
SourcePackage: upstart
UpgradeStatus: No upgrade log present (probably fresh install)
UpstartBugCategory: System
UpstartRunningSystemVersion: init (upstart 1.10)