Add a 'start' command

When any non-global-flag parameter appears on the command line make sure
there's a "command" even in the 'start' (run) case to ensure its not
ambiguous as to what the arg is. For example, w/o this fix its not
clear if
   runc foo
means 'foo' is the name of a config file or an unknown command.  Or worse,
you can't name a config file the same a ANY command, even future (yet to
be created) commands.

We should fix this now before we ship 1.0 and are forced to support this
ambiguous case for a long time.

Signed-off-by: Doug Davis <dug@us.ibm.com>

README.md

@@ -29,11 +29,9 @@ sudo make install
 
 ### Using:
 
-To run a container that you received just execute `runc` with the JSON format as the argument or have a
+To run a container, execute `runc start` in the bundle's root directory:
-`config.json` file in the current working directory.
-
 ```bash
-runc
+runc start
 / $ ps
 PID   USER     COMMAND
 1     daemon   sh
@@ -41,6 +39,18 @@ PID   USER     COMMAND
 / $
 ```
 
+Or you can specify the path to a JSON configuration file:
+```bash
+runc start config.json
+/ $ ps
+PID   USER     COMMAND
+1     daemon   sh
+5     daemon   sh
+/ $
+```
+Note: the use of the `start` command is required when specifying a 
+configuration file.
+
 ### OCF Container JSON Format:
 
 Below is a sample `config.json` configuration file. It assumes that
@@ -210,9 +220,9 @@ tar -C rootfs -xf busybox.tar
 ```
 * Create a file called `config.json` using the example from above.  You can also
 generate a spec using `runc spec`, redirecting the output into `config.json`
-* Execute `runc` and you should be placed into a shell where you can run `ps`:
+* Execute `runc start` and you should be placed into a shell where you can run `ps`:
 ```
-$ runc
+$ runc start
 / # ps
 PID   USER     COMMAND
     1 root     sh

main.go

@@ -24,7 +24,11 @@ After creating a spec for your root filesystem with runc, you can execute a
 container in your shell by running:
 
     cd /mycontainer
-    runc  [ spec-file ]
+    runc start
+
+or
+	cd /mycontainer
+	runc start [ spec-file ]
 
 If not specified, the default value for the 'spec-file' is 'config.json'. `
 )
@@ -56,6 +60,7 @@ func main() {
 		},
 	}
 	app.Commands = []cli.Command{
+		startCommand,
 		checkpointCommand,
 		eventsCommand,
 		restoreCommand,
@@ -69,7 +74,8 @@ func main() {
 		return nil
 	}
 
-	app.Action = runAction
+	// Default to 'start' is no command is specified
+	app.Action = startCommand.Action
 
 	if err := app.Run(os.Args); err != nil {
 		logrus.Fatal(err)

start.go

@@ -13,6 +13,33 @@ import (
 	"github.com/opencontainers/specs"
 )
 
+var startCommand = cli.Command{
+	Name:  "start",
+	Usage: "create and run a container",
+	Action: func(context *cli.Context) {
+		spec, err := loadSpec(context.Args().First())
+
+		notifySocket := os.Getenv("NOTIFY_SOCKET")
+		if notifySocket != "" {
+			setupSdNotify(spec, notifySocket)
+		}
+
+		if err != nil {
+			fatal(err)
+		}
+		if os.Geteuid() != 0 {
+			logrus.Fatal("runc should be run as root")
+		}
+		status, err := startContainer(context, spec)
+		if err != nil {
+			logrus.Fatalf("Container start failed: %v", err)
+		}
+		// exit with the container's exit status so any external supervisor is
+		// notified of the exit with the correct exit status.
+		os.Exit(status)
+	},
+}
+
 func init() {
 	if len(os.Args) > 1 && os.Args[1] == "init" {
 		runtime.GOMAXPROCS(1)
@@ -25,7 +52,7 @@ func init() {
 	}
 }
 
-func execContainer(context *cli.Context, spec *specs.LinuxSpec) (int, error) {
+func startContainer(context *cli.Context, spec *specs.LinuxSpec) (int, error) {
 	config, err := createLibcontainerConfig(context.GlobalString("id"), spec)
 	if err != nil {
 		return -1, err
@@ -65,28 +92,6 @@ func execContainer(context *cli.Context, spec *specs.LinuxSpec) (int, error) {
 }
 
 // default action is to execute a container
-func runAction(context *cli.Context) {
-	spec, err := loadSpec(context.Args().First())
-
-	notifySocket := os.Getenv("NOTIFY_SOCKET")
-	if notifySocket != "" {
-		setupSdNotify(spec, notifySocket)
-	}
-
-	if err != nil {
-		fatal(err)
-	}
-	if os.Geteuid() != 0 {
-		logrus.Fatal("runc should be run as root")
-	}
-	status, err := execContainer(context, spec)
-	if err != nil {
-		logrus.Fatalf("Container start failed: %v", err)
-	}
-	// exit with the container's exit status so any external supervisor is
-	// notified of the exit with the correct exit status.
-	os.Exit(status)
-}
 
 // If systemd is supporting sd_notify protocol, this function will add support
 // for sd_notify protocol from within the container.