Ignore prompt if stdin not a tty on machine start

When starting a machine and the user has not explicitly passed
-u=true|false AND stdin is a not a tty, we should not prompt to update
connections.

Fixes: #27556

Signed-off-by: Brent Baude <bbaude@redhat.com>

docs/source/markdown/options/update-connection.md

@@ -7,7 +7,8 @@
 When used in conjunction with `podman machine init --now` or `podman machine start`, this option sets the
 associated machine system connection as the default. When using this option, a `-u` or `-update-connection` will
 set the value to true.  To set this value to false, meaning no change and no prompting,
-use `--update-connection=false`.
+use `--update-connection=false`. If the value is unset and stdin is not a tty, no prompt or update
+shall occur.
 
 If the value is set to true, the machine connection will be set as the system default.
 If the value is set to false, the system default will be unchanged.

pkg/machine/e2e/start_test.go

@@ -1,6 +1,7 @@
 package e2e_test
 
 import (
+	"bytes"
 	"fmt"
 	"net"
 	"net/url"
@@ -135,22 +136,28 @@ var _ = Describe("podman machine start", func() {
 	})
 
 	It("start only starts specified machine", func() {
-		i := initMachine{}
-		startme := randomString()
-		session, err := mb.setName(startme).setCmd(i.withImage(mb.imagePath)).run()
-		Expect(err).ToNot(HaveOccurred())
-		Expect(session).To(Exit(0))
-
 		j := initMachine{}
 		dontstartme := randomString()
 		session2, err := mb.setName(dontstartme).setCmd(j.withFakeImage(mb)).run()
 		Expect(err).ToNot(HaveOccurred())
 		Expect(session2).To(Exit(0))
 
+		i := initMachine{}
+		startme := randomString()
+		session, err := mb.setName(startme).setCmd(i.withImage(mb.imagePath)).run()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(session).To(Exit(0))
+
 		s := &startMachine{}
-		session3, err := mb.setName(startme).setCmd(s).setTimeout(time.Minute * 10).run()
+		// Provide a buffer as stdin to simulate non-tty input (e.g., piped or redirected stdin)
+		// When stdin is not a tty, the command should not prompt for connection updates
+		stdinBuf := bytes.NewBufferString("n\n")
+		session3, err := mb.setName(startme).setCmd(s).setTimeout(time.Minute * 10).setStdin(stdinBuf).run()
 		Expect(err).ToNot(HaveOccurred())
 		Expect(session3).Should(Exit(0))
+		// Verify that the prompt message did not appear (no prompting when stdin is not a tty)
+		combinedOutput := session3.outputToString() + session3.errorToString()
+		Expect(combinedOutput).ToNot(ContainSubstring("Set the default Podman connection to this machine"), "should not prompt when stdin is not a tty")
 
 		inspect := new(inspectMachine)
 		inspect = inspect.withFormat("{{.State}}")

pkg/machine/shim/host.go

@@ -29,6 +29,7 @@ import (
 	"github.com/hashicorp/go-multierror"
 	"github.com/sirupsen/logrus"
 	"go.podman.io/common/pkg/config"
+	"golang.org/x/term"
 )
 
 // List is done at the host level to allow for a *possible* future where
@@ -501,8 +502,11 @@ func Start(mc *vmconfigs.MachineConfig, mp vmconfigs.VMProvider, opts machine.St
 	// Do not do anything with the system connection if its already
 	// the default system connection.
 	if !conn.Default {
-		// Prompt for system connection update
+		if updateSystemConn != nil {
-		if updateSystemConn == nil {
+			updateDefaultConnection = *updateSystemConn
+		} else if term.IsTerminal(int(os.Stdin.Fd())) {
+			// Prompt for system connection update if there is a terminal
+			// on stdin
 			response, err := promptUpdateSystemConn()
 			if err != nil {
 				return err
@@ -517,8 +521,6 @@ func Start(mc *vmconfigs.MachineConfig, mp vmconfigs.VMProvider, opts machine.St
 				fmt.Println("Default system connection will remain unchanged")
 			}
 			updateDefaultConnection = response
-		} else {
-			updateDefaultConnection = *updateSystemConn
 		}
 	}