(tail_forever): Don't call kill if pid is 0.

Detect when `writer_is_dead' also when the writer is some other user.
From Karl Heuer.

(parse_options): Warn if --pid=PID is used without -f.

diff --git a/src/tail.c b/src/tail.c
index b8109dd..e6f9b42 100644 (file)
--- a/src/tail.c
+++ b/src/tail.c
@@ -922,7 +922,12 @@ tail_forever (struct File_spec *f, int nfiles)
 
          /* Once the writer is dead, read the files once more to
             avoid a race condition.  */
-         writer_is_dead = (kill (pid, 0) != 0);
+         writer_is_dead = (pid != 0
+                           && kill (pid, 0) != 0
+                           /* Handle the case in which you cannot send a
+                              signal to the writer, so kill fails and sets
+                              errno to EPERM.  */
+                           && errno != EPERM);
        }
     }
 }
@@ -1426,6 +1431,10 @@ parse_options (int argc, char **argv,
 
   if (reopen_inaccessible_files && follow_mode != Follow_name)
     error (0, 0, _("warning: --retry is useful only when following by name"));
+
+  if (pid && !forever)
+    error (0, 0,
+          _("warning: PID ignored; --pid=PID is useful only when following"));
 }
 
 int