diff --git a/qemu/bin/first-free-port b/qemu/bin/first-free-port
new file mode 100755
index 0000000..886a367
--- /dev/null
+++ b/qemu/bin/first-free-port
@@ -0,0 +1,34 @@
+#!/usr/bin/env sh
+#set -x
+
+name=$(basename "$0")
+used_tcp_ports=$(sed 1d /proc/net/tcp \
+    | awk '($4 == "0A") { print $2 }' \
+    | awk -F : '($1 == "00000000" || $1 == "0100007F") { print $2 }' \
+    | perl -e 'foreach my $line (<>) { print hex($line) . "\n"; }'
+)
+
+perror() {
+  >&2 printf "%s: %s\n" "$name" "$*"
+}
+
+port_is_free() {
+  for used_port in $used_tcp_ports; do
+    [ "$port" = "$used_port" ] && return 1
+  done
+
+  :
+}
+
+port=$1
+
+if ! { [ "$port" -gt 0 ] && [ "$port" -lt 65536 ]; } 2> /dev/null; then
+  perror "you must specify a valid TCP port"
+  exit 1
+fi
+
+while ! port_is_free; do
+  port=$((port + 1))
+done
+
+printf %s\\n "$port"