This file is indexed.

/usr/include/x86_64-linux-gnu/bits/a.out.h is in libc6-dev 2.15-0ubuntu10.18.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
#ifndef __A_OUT_GNU_H__
# error "Never use <bits/a.out.h> directly; include <a.out.h> instead."
#endif

#include <bits/wordsize.h>

#if __WORDSIZE == 64

/* Signal to users of this header that this architecture really doesn't
   support a.out binary format.  */
#define __NO_A_OUT_SUPPORT 1

#endif