openwrt dhcp client

udhcpc -p /var/run/udhcpc-eth0.pid -s /lib/netifd/dhcp.script

udhcpc -i eth1

root@OpenWrt:~# udhcpc --help
BusyBox v1.23.2 (2017-07-28 16:20:17 PDT) multi-call binary.

Usage: udhcpc [-fbqRB] [-t N] [-T SEC] [-A SEC/-n]
[-i IFACE] [-s PROG] [-p PIDFILE]
[-oC] [-r IP] [-V VENDOR] [-F NAME] [-x OPT:VAL]... [-O OPT]...

-i,--interface IFACE Interface to use (default eth0)
-s,--script PROG Run PROG at DHCP events (default /usr/share/udhcpc/default.script)
-p,--pidfile FILE Create pidfile
-B,--broadcast Request broadcast replies
-t,--retries N Send up to N discover packets (default 3)
-T,--timeout SEC Pause between packets (default 3)
-A,--tryagain SEC Wait if lease is not obtained (default 20)
-n,--now Exit if lease is not obtained
-q,--quit Exit after obtaining lease
-R,--release Release IP on exit
-f,--foreground Run in foreground
-b,--background Background if lease is not obtained
-S,--syslog Log to syslog too
-r,--request IP Request this IP address
-o,--no-default-options Don't request any options (unless -O is given)
-O,--request-option OPT Request option OPT from server (cumulative)
-x OPT:VAL Include option OPT in sent packets (cumulative)
Examples of string, numeric, and hex byte opts:
-x hostname:bbox - option 12
-x lease:3600 - option 51 (lease time)
-x 0x3d:0100BEEFC0FFEE - option 61 (client id)
-F,--fqdn NAME Ask server to update DNS mapping for NAME
-V,--vendorclass VENDOR Vendor identifier (default 'udhcp VERSION')
-C,--clientid-none Don't send MAC as client identifier
Signals:
USR1 Renew lease
USR2 Release lease

root@OpenWrt:~#

root@OpenWrt:/lib/netifd# cat dhcp.script
#!/bin/sh
[ -z "$1" ] && echo "Error: should be run by udhcpc" && exit 1

. /lib/functions.sh
. /lib/netifd/netifd-proto.sh

set_classless_routes() {
local max=128
while [ -n "$1" -a -n "$2" -a $max -gt 0 ]; do
proto_add_ipv4_route "${1%%/*}" "${1##*/}" "$2" "$ip"
max=$(($max-1))
shift 2
done
}

setup_interface () {
proto_init_update "*" 1
proto_add_ipv4_address "$ip" "${subnet:-255.255.255.0}"
# TODO: apply $broadcast

for i in $router; do
proto_add_ipv4_route "$i" 32 "" "$ip"
proto_add_ipv4_route 0.0.0.0 0 "$i" "$ip"

for r in $CUSTOMROUTES; do
proto_add_ipv4_route "${r%%/*}" "${r##*/}" "$i" "$ip"
done
done

# CIDR STATIC ROUTES (rfc3442)
[ -n "$staticroutes" ] && set_classless_routes $staticroutes
[ -n "$msstaticroutes" ] && set_classless_routes $msstaticroutes

for dns in $dns; do
proto_add_dns_server "$dns"
done
for domain in $domain; do
proto_add_dns_search "$domain"
done

proto_add_data
[ -n "$ZONE" ]     && json_add_string zone "$ZONE"
[ -n "$ntpsrv" ]   && json_add_string ntpserver "$ntpsrv"
[ -n "$timesvr" ]  && json_add_string timeserver "$timesvr"
[ -n "$hostname" ] && json_add_string hostname "$hostname"
[ -n "$message" ]  && json_add_string message "$message"
[ -n "$timezone" ] && json_add_int timezone "$timezone"
[ -n "$lease" ]    && json_add_int leasetime "$lease"
proto_close_data

proto_send_update "$INTERFACE"


if [ "$IFACE6RD" != 0 -a -n "$ip6rd" ]; then
local v4mask="${ip6rd%% *}"
ip6rd="${ip6rd#* }"
local ip6rdprefixlen="${ip6rd%% *}"
ip6rd="${ip6rd#* }"
local ip6rdprefix="${ip6rd%% *}"
ip6rd="${ip6rd#* }"
local ip6rdbr="${ip6rd%% *}"

[ -n "$ZONE" ] || ZONE=$(fw3 -q network $INTERFACE)
[ -z "$IFACE6RD" -o "$IFACE6RD" = 1 ] && IFACE6RD=${INTERFACE}_6

json_init
json_add_string name "$IFACE6RD"
json_add_string ifname "@$INTERFACE"
json_add_string proto "6rd"
json_add_string peeraddr "$ip6rdbr"
json_add_int ip4prefixlen "$v4mask"
json_add_string ip6prefix "$ip6rdprefix"
json_add_int ip6prefixlen "$ip6rdprefixlen"
json_add_string tunlink "$INTERFACE"
[ -n "$IFACE6RD_DELEGATE" ] && json_add_boolean delegate "$IFACE6RD_DELEGATE"
[ -n "$ZONE6RD" ] || ZONE6RD=$ZONE
[ -n "$ZONE6RD" ] && json_add_string zone "$ZONE6RD"
[ -n "$MTU6RD" ] && json_add_string mtu "$MTU6RD"
json_close_object

ubus call network add_dynamic "$(json_dump)"
fi
}

deconfig_interface() {
proto_init_update "*" 0
proto_send_update "$INTERFACE"
}

case "$1" in
deconfig)
deconfig_interface
;;
renew|bound)
setup_interface
;;
esac

# user rules
[ -f /etc/udhcpc.user ] && . /etc/udhcpc.user "$@"

exit 0