errno errors reported as such.

src/service/libc.cr

@@ -25,14 +25,11 @@ module System
 
 		passwd = pointer.value
 
-		# FIXME: Probably should get some errno magic right now.
+		r = LibC.setgid passwd.pw_gid
-		if 0 != LibC.setuid passwd.pw_uid
+		raise Errno.new "setgid" if r != 0
-			raise Exception.new "setuid failed"
-		end
 
-		if 0 != LibC.setgid passwd.pw_gid
+		r = LibC.setuid passwd.pw_uid
-			raise Exception.new "setuid failed"
+		raise Errno.new "setuid" if r != 0
-		end
 
 		passwd
 	end