getty: Make namespacing more obvious

Warn the user in the MOTD
Add "(ns: getty)" or "(ns: sshd)" to the PS1
Use `agetty` and `-a root` to ensure we get a login shell when insecure

Signed-off-by: Dave Tucker <dt@docker.com>

pkg/getty/etc/motd

@@ -1 +1,4 @@
-Welcome to LinuxKit 
+Welcome to LinuxKit!
+
+NOTE: This system is namespaced.
+The namespace you are currently in may not be the root.

pkg/getty/etc/profile.d/namespace.sh

@@ -0,0 +1 @@
+export PS1="(ns: getty) $PS1"

pkg/getty/usr/bin/rungetty.sh

@@ -31,14 +31,14 @@ start_getty() {
 	# are we secure or insecure?
 	loginargs=
 	if [ "$INSECURE" == "true" ]; then
-		loginargs="-n -l /bin/sh"
+		loginargs="-a root"
 	fi
 
 	if ! grep -q -w "$tty" "$securetty"; then
 		echo "$tty" >> "$securetty"
 	fi
 	# respawn forever
-	infinite_loop setsid.getty -w /sbin/getty $loginargs $line $speed $tty $term &
+	infinite_loop setsid.getty -w /sbin/agetty $loginargs $line $speed $tty $term &
 }
 
 # check if we have /etc/getty.shadow

pkg/sshd/etc/motd

@@ -1 +1,4 @@
-Welcome to LinuxKit 
+Welcome to LinuxKit!
+
+NOTE: This system is namespaced.
+The namespace you are currently in may not be the root.

pkg/sshd/etc/profile.d/namespace.sh

@@ -0,0 +1 @@
+export PS1="(ns: sshd) $PS1"