/lib/live/boot/9990-netbase.sh is in live-boot 3.0.1-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 | #!/bin/sh
#set -e
Netbase ()
{
	if [ -n "${NONETWORKING}" ]
	then
		return
	fi
	# FIXME: stop hardcoding overloading of initramfs-tools functions
	. /scripts/functions
	. /lib/live/boot/9990-initramfs-tools.sh
	log_begin_msg "Preconfiguring networking"
	IFFILE="/root/etc/network/interfaces"
	DNSFILE="/root/etc/resolv.conf"
	if [ "${STATICIP}" = "frommedia" ] && [ -e "${IFFILE}" ]
	then
		# will use existent /etc/network/interfaces
		log_end_msg
		return
	fi
cat > "${IFFILE}" << EOF
auto lo
iface lo inet loopback
EOF
	udevadm trigger
	udevadm settle
	if [ -z "${NETBOOT}" ] && [ -n "${STATICIP}" ] && [ "${STATICIP}" != "frommedia" ]
	then
		parsed=$(echo "${STATICIP}" | sed -e 's|,| |g')
		for ifline in ${parsed}
		do
			ifname="$(echo ${ifline} | cut -f1 -d ':')"
			ifaddress="$(echo ${ifline} | cut -f2 -d ':')"
			ifnetmask="$(echo ${ifline} | cut -f3 -d ':')"
			ifgateway="$(echo ${ifline} | cut -f4 -d ':')"
			nameserver="$(echo ${ifline} | cut -f5 -d ':')"
cat >> "${IFFILE}" << EOF
allow-hotplug ${ifname}
iface ${ifname} inet static
    address ${ifaddress}
    netmask ${ifnetmask}
EOF
			if [ -n "${ifgateway}" ]
			then
cat >> "${IFFILE}" << EOF
    gateway ${ifgateway}
EOF
			fi
			if [ -n "${nameserver}" ]
			then
				if [ -e "${DNSFILE}" ]
				then
					grep -v ^nameserver "${DNSFILE}" > "${DNSFILE}.tmp"
					mv "${DNSFILE}.tmp" "${DNSFILE}"
				fi
				echo "nameserver ${nameserver}" >> "${DNSFILE}"
			fi
		done
	else
		if [ -z "${NETBOOT}" ] || [ -n "${DHCP}" ]
		then
			# default, dhcp assigned
			method="dhcp"
		else
			# make sure that the preconfigured interface would not get reassigned by dhcp
			# on startup by ifup script - otherwise our root fs might be disconnected!
			method="manual"
		fi
		# iterate the physical interfaces and add them to the interfaces list and also add when ethdevice= called on cmdline
		if [ "${method}" != dhcp ] || ([ ! -x /root/usr/sbin/NetworkManager ] && [ ! -x /root/usr/sbin/wicd ]) || [ ! -z "${ETHDEVICE}" ]
		then
			for interface in /sys/class/net/eth* /sys/class/net/ath* /sys/class/net/wlan*
			do
				[ -e ${interface} ] || continue
				i="$(basename ${interface})"
cat >> "${IFFILE}" << EOF
allow-hotplug ${i}
iface ${i} inet ${method}
EOF
			done
		fi
		if [ ! -f /root/etc/resolv.conf ] || [ -z "$(cat /root/etc/resolv.conf)" ]
		then
			if [ -f /netboot.config ]
			then
				# create a resolv.conf if it is not present or empty
				cp /netboot.config /root/var/log/netboot.config
				rc_search=$(cat netboot.config | awk '/domain/{print $3}')
				rc_server0=$(cat netboot.config | awk '/dns0/{print $5}')
				rc_server1=$(cat netboot.config | awk '/dns0/{print $8}')
				rc_server0="nameserver ${rc_server0}"
				if [ "${rc_server1}" = "0.0.0.0" ]
				then
					rc_server1=""
				else
					rc_server1="nameserver ${rc_server1}"
				fi
cat > /root/etc/resolv.conf << EOF
# /etc/resolv.conf
# Autogenerated by live-boot
search ${rc_search}
domain ${rc_search}
${rc_server0}
${rc_server1}
EOF
				cat /root/etc/resolv.conf >> /root/var/log/netboot.config
			fi
		fi
	fi
	log_end_msg
}
 |