In systemd I have seen this error, using it as a service:

vlock-start[14567]: vlock-new: could not activate new terminal: Interrupted system call

I think this should fix that.

diff --git a/modules/new.c b/modules/new.c
index e9b15fb..1f692fd 100644
--- a/modules/new.c
+++ b/modules/new.c
@@ -103,7 +103,10 @@ static char *get_console_name(int n)
  * file descriptor. */
 static int activate_console(int consfd, int vtno)
 {
-  int c = ioctl(consfd, VT_ACTIVATE, vtno);
+  int c;
+  do {
+    c = ioctl(consfd, VT_ACTIVATE, vtno);
+  } while(c != 0 && errno == EINTR);
 
   return c < 0 ? c : ioctl(consfd, VT_WAITACTIVE, vtno);
 }