diff --git a/gtests/net/packetdrill/in_netns.sh b/gtests/net/packetdrill/in_netns.sh
index ef1f72c7..31ae29d1 100755
--- a/gtests/net/packetdrill/in_netns.sh
+++ b/gtests/net/packetdrill/in_netns.sh
@@ -12,15 +12,27 @@ setup() {
 	ip netns add "${NETNS}"
 	ip -netns "${NETNS}" link set lo up
 	if [ -n "${TCPDUMP_OUTPUT}" ]; then
-		ip netns exec "${NETNS}" tcpdump -i any -s 150 -w "${TCPDUMP_OUTPUT}" &
+		mkdir -p "$(dirname "${TCPDUMP_OUTPUT}")"
+
+		ip netns exec "${NETNS}" tcpdump -i any -s 150 --immediate-mode --packet-buffered -w "${TCPDUMP_OUTPUT}" &
 		TCPDUMP_PID=$!
-		sleep 1 # give some time to TCPDump to start
+
+		# give some time to TCPDump to start
+		for _ in $(seq 10); do
+			[ -s "${TCPDUMP_OUTPUT}" ] && break
+			# BusyBox's sleep doesn't support float numbers, just wait 1 sec
+			if ! sleep 0.1 2>/dev/null; then
+				sleep 1
+				break
+			fi
+		done
 	fi
 }
 
 cleanup() {
 	if [ -n "${TCPDUMP_PID}" ]; then
-		sleep 1 # give some time to TCPDump to process the packets
+		# give some time to TCPDump to get the last packets
+		sleep 0.1 2>/dev/null || sleep 1
 		kill "${TCPDUMP_PID}"
 		wait "${TCPDUMP_PID}" 2>/dev/null || true
 	fi