[Unit]
Description=ISC DHCP IPv4 server
Documentation=man:dhcpd(8)
Wants=network-online.target
After=network-online.target
After=time-sync.target
ConditionPathExists=/etc/default/isc-dhcp-server
ConditionPathExists=|/etc/ltsp/dhcpd.conf
ConditionPathExists=|/etc/dhcp/dhcpd.conf

[Service]
EnvironmentFile=/etc/default/isc-dhcp-server
RuntimeDirectory=dhcp-server
# Allow dhcp server to write lease and pid file as 'dhcpd' user
ExecStartPre=/bin/sh -ec '\
    DHCPD_PID_DIR=`/usr/bin/dirname $DHCPD_PID`; \
    /bin/chown dhcpd:dhcpd $DHCPD_PID_DIR'
# The leases files need to be root:root even when dropping privileges
ExecStart=/bin/sh -ec '\
    CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
    if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
    [ -e /var/lib/dhcp/dhcpd.leases ] || touch /var/lib/dhcp/dhcpd.leases; \
    chown root:root /var/lib/dhcp /var/lib/dhcp/dhcpd.leases*; \
    exec dhcpd -user dhcpd -group dhcpd -f -4 -pf $DHCPD_PID -cf $CONFIG_FILE $INTERFACES'

[Install]
WantedBy=multi-user.target