@@ -4,6 +4,7 @@ package main

 import (

 	"fmt"

+	"net"

 	"net/http"

 	"os"

 	"path/filepath"

@@ -1317,3 +1318,14 @@ func (s *DockerSwarmSuite) TestAPISwarmUnlockNotLocked(c *check.C) {

 	c.Assert(err, checker.NotNil)

 	c.Assert(err.Error(), checker.Contains, "swarm is not locked")

 }

+

+// #29885

+func (s *DockerSwarmSuite) TestAPISwarmErrorHandling(c *check.C) {

+	ln, err := net.Listen("tcp", fmt.Sprintf(":%d", defaultSwarmPort))

+	c.Assert(err, checker.IsNil)

+	defer ln.Close()

+	d := s.AddDaemon(c, false, false)

+	err = d.Init(swarm.InitRequest{})

+	c.Assert(err, checker.NotNil)

+	c.Assert(err.Error(), checker.Contains, "address already in use")

+}