sonic-buildimage/dockers/docker-dhcp-relay/start.sh

#!/usr/bin/env bash

# Remove stale rsyslog PID file if it exists
rm -f /var/run/rsyslogd.pid

# Start rsyslog
supervisorctl start rsyslogd

# If our supervisor config has entries in the "isc-dhcp-relay" group...
if [ $(supervisorctl status | grep -c "^isc-dhcp-relay:") -gt 0 ]; then
    # Wait for all interfaces to come up and be assigned IPv4 addresses before
    # starting the DHCP relay agent(s). If an interface the relay should listen
    # on is down, the relay agent will not start. If an interface the relay
    # should listen on is up but does not have an IP address assigned when the
    # relay agent starts, it will not listen or send on that interface for the
    # lifetime of the process.
    /usr/bin/wait_for_intf.sh

    # Start all DHCP relay agent(s)
    supervisorctl start isc-dhcp-relay:*
fi

# If our supervisor config has entries in the "dhcpmon" group...
if [ $(supervisorctl status | grep -c "^dhcpmon:") -gt 0 ]; then
    # Start all DHCP Monitor daemon(s)
    supervisorctl start dhcpmon:*
fi