fix: close stale ControlMaster ssh connection for machine init/add

internal/cli/cli.go

@@ -547,26 +547,35 @@ func provisionOrConnectRemoteMachine(
 	}
 
 	// Use the system 'ssh' command (default).
-	exec := sshexec.NewSSHCLIRemote(
-		remoteMachine.User,
-		remoteMachine.Host,
-		remoteMachine.Port,
-		remoteMachine.KeyPath,
-	)
-
-	if !skipInstall {
-		if err := provisionMachine(ctx, exec, version); err != nil {
-			return nil, fmt.Errorf("provision machine: %w", err)
-		}
-	}
-
 	sshConfig := &connector.SSHConnectorConfig{
 		User:    remoteMachine.User,
 		Host:    remoteMachine.Host,
 		Port:    remoteMachine.Port,
 		KeyPath: remoteMachine.KeyPath,
 	}
-	machineClient, err := client.New(ctx, connector.NewSSHCLIConnector(sshConfig))
+	conn := connector.NewSSHCLIConnector(sshConfig)
+
+	if !skipInstall {
+		exec := sshexec.NewSSHCLIRemote(
+			remoteMachine.User,
+			remoteMachine.Host,
+			remoteMachine.Port,
+			remoteMachine.KeyPath,
+		)
+		if err := provisionMachine(ctx, exec, version); err != nil {
+			return nil, fmt.Errorf("provision machine: %w", err)
+		}
+
+		if remoteMachine.User != rootUser {
+			// provisionMachine has just added the user to the uncloud group. Any SSH ControlMaster left over from
+			// a previous uc invocation (e.g. a failed uc command against the uninitialised machine) still holds
+			// the old user groups and would deny access to /run/uncloud/uncloud.sock. Close the current session
+			// if it exists so the next session picks up the new groups.
+			conn.CloseControlMaster(ctx)
+		}
+	}
+
+	machineClient, err := client.New(ctx, conn)
 	if err != nil {
 		return nil, fmt.Errorf("connect to remote machine: %w", err)
 	}

internal/cli/machine.go

@@ -72,6 +72,17 @@ func provisionMachine(ctx context.Context, exec sshexec.Executor, version string
 						"   echo '%[1]s ALL=(ALL) NOPASSWD:ALL' | sudo tee /etc/sudoers.d/%[1]s",
 					user)
 			}
+			if strings.Contains(err.Error(), "not in the sudoers file") {
+				return fmt.Errorf(
+					"user '%[1]s' is not in the sudo group or sudoers file so cannot use sudo, but Uncloud needs "+
+						"passwordless sudo or root access to install and configure the uncloudd daemon on the remote "+
+						"machine.\n\n"+
+						"Possible solutions:\n"+
+						"1. Use root user or a user with passwordless sudo instead.\n"+
+						"2. Grant passwordless sudo to the user '%[1]s' by running on the remote machine as root:\n"+
+						"   echo '%[1]s ALL=(ALL) NOPASSWD:ALL' > /etc/sudoers.d/%[1]s",
+					user)
+			}
 			return fmt.Errorf("sudo command failed for user '%s': %w. "+
 				"Please ensure the user has sudo privileges or use root user instead", user, err)
 		}

pkg/client/connector/sshcli.go

@@ -207,6 +207,16 @@ func (c *SSHCLIConnector) CheckTCPForwarding(ctx context.Context) error {
 	return c.fwdCheckErr
 }
 
+// CloseControlMaster terminates the SSH ControlMaster process for this destination so the next connection starts
+// a fresh SSH session. No-op if no master is running or the control socket is not configured. Errors are ignored.
+func (c *SSHCLIConnector) CloseControlMaster(ctx context.Context) {
+	if c.controlSockPath == "" {
+		return
+	}
+	args := append(c.buildSSHArgs(), "-O", "exit")
+	_ = exec.CommandContext(ctx, "ssh", args...).Run()
+}
+
 func (c *SSHCLIConnector) Close() error {
 	// Individual connections are managed by gRPC and closed when the gRPC connection closes.
 	// The SSH control socket may persist for connection reuse across CLI invocations.