Fix #247: fall back to reboot -f in sulogin mode

When logged in from sulogin we cannot send IPC to Finit, not even
signals, to delegate reboot.  For usability, attempt to tell reboot that
it's in sulogin mode -- provided the bundled sulogin is used -- to let
reboot trigger over to forced reboot.

We cannot do much about initctl, just document this as a limitation.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/reboot.c

@@ -26,6 +26,7 @@
 #include <getopt.h>
 #include <signal.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include "util.h"
@@ -159,6 +160,10 @@ int reboot_main(int argc, char *argv[])
 	/* Check for any overrides */
 	transform(NULL);
 
+	/* Check if we're in sulogin shell */
+	if (getenv("SULOGIN"))
+		force = 1;
+
 	if (force) {
 		sync();