vm: More precise "free port" detection

22000 is used by syncthing, and it resets the connection. Specifically
search for a refused connection.

diff --git a/vm b/vm
index 0f14fea1aae50c1d9d4a9290a2a03f91bf303767..53231328f6b5b7f35e478fe52754c1be331eef7d 100755 (executable)
--- a/vm
+++ b/vm
@@ -5,7 +5,7 @@ image="$1"
 shift
 # determine ssh forward port
 ssh_port=22000
-while echo '' | nc localhost $ssh_port >/dev/null; do
+until echo '' | nc localhost $ssh_port 2>&1 >/dev/null | grep -q 'Connection refused'; do
     ssh_port=$((ssh_port+1))
 done
 echo "Host ssh port: $ssh_port"