Fix blank network settings when DHCP is slow.

postinstall/init.sh

@@ -1,13 +1,48 @@
 #!/usr/bin/env bash
 
-# Get the current DHCP network address, gateway and DNS servers
-NIC=$(ip link | grep "^2:" | awk '{print $2}' | tr -d ":")
-IP_ADDRESS=$(ip address show ${NIC} | grep -E "inet " | awk '{print $2}')
-NETMASK=$(echo ${IP_ADDRESS} | sed 's/.*\///')
-IP_ADDRESS=$(echo ${IP_ADDRESS} | sed 's/\/.*//')
-GATEWAY=$(ip route | grep "default" | awk '{print $3}')
+# Get the current DHCP network address, gateway and DNS servers.  DHCP can
+# still be completing when this service starts, even after network-online.
+get_network_settings() {
+  local cidr_address
+
+  # Clear every value before each attempt so a partial/stale DHCP lease can
+  # never be written to the static network configuration.
+  NIC=""
+  IP_ADDRESS=""
+  NETMASK=""
+  GATEWAY=""
+  DNS_SERVERS=""
+
+  NIC=$(ip link | awk -F ': ' '$1 == 2 {sub(/@.*/, "", $2); print $2; exit}')
+  [ -n "${NIC}" ] || return 1
+
+  cidr_address=$(ip -4 address show "${NIC}" | awk '/inet / {print $2; exit}')
+  [ -n "${cidr_address}" ] || return 1
+
+  IP_ADDRESS=${cidr_address%/*}
+  NETMASK=${cidr_address#*/}
+  GATEWAY=$(ip route show default | awk 'NR == 1 {print $3}')
   DNS_SERVERS=$(awk '/^nameserver/ {print $2}' /etc/resolv.conf | xargs)
 
+  [ -n "${IP_ADDRESS}" ] && [ -n "${NETMASK}" ] && \
+    [ -n "${GATEWAY}" ] && [ -n "${DNS_SERVERS}" ]
+}
+
+MAX_NETWORK_ATTEMPTS=10
+for attempt in $(seq 1 "${MAX_NETWORK_ATTEMPTS}"); do
+  if get_network_settings; then
+    break
+  fi
+
+  if [ "${attempt}" -eq "${MAX_NETWORK_ATTEMPTS}" ]; then
+    echo "DHCP network settings were incomplete after ${MAX_NETWORK_ATTEMPTS} attempts; aborting postinstall." >&2
+    exit 1
+  fi
+
+  echo "DHCP network settings are not ready (attempt ${attempt}/${MAX_NETWORK_ATTEMPTS}); retrying in 3 seconds." >&2
+  sleep 3
+done
+
 # Tear down DHCP first, while interfaces is still dhcp, so dhcpcd is gone
 # before we write a static resolv.conf (otherwise it rewrites it on exit)
 ifdown "${NIC}" || true