[Caml-list] Re: Unix.getlogin () fails when stdin is redirected

["Ricardo Catalinas Jiménez" <jimenezrick@gmail.com>]

On Tue, Mar 20, 2012 at 06:51:13PM +0100, Ricardo Catalinas Jiménez wrote:
> I found out the next issue in this simple code:
> 
> let () =
>     print_endline "Hello";
>     print_endline (Unix.getlogin ())
> 
> Running in the normal case, with `./a.out' gives:
> 
> Hello
> ricardo
> 
> But running like `./a.out </dev/null' makes Unix.getlogin fail:
> 
> Hello
> Fatal error: exception Unix.Unix_error(20, "getlogin", "")
> 
> A simple strace reveals the problem:
> 
>    open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
>    fstat(3, {st_mode=S_IFREG|0644, st_size=509, ...}) = 0
>    mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb125554000
>    read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 509
>    read(3, "", 4096)                       = 0
>    close(3)                                = 0
>    munmap(0x7fb125554000, 4096)            = 0
> -> ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7fff12682c98) = -1 ENOTTY (Inappropriate ioctl for device)
>    write(2, "Fatal error: exception Unix.Unix"..., 59) = 59
>    exit_group(2)                           = ?


Someone knew the answer, man 3 getlogin reads:

       Note that glibc does not follow the POSIX specification and uses
       stdin instead of /dev/tty.  A bug.  (Other recent systems, like
       SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8 all return the login
       name also when stdin is redirected.)


Regards
-- 
Ricardo (http://r.untroubled.be/)