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

[David House <dhouse@janestreet.com>]

Note that Jane Street's core library [1] does not use getlogin(3) in 
its replacement Unix module, for exactly this reason:

(* The standard getlogin function goes through utmp which is unreliable,
   see the BUGS section of getlogin(3) *)
let getlogin_orig = Unix.getlogin
let getlogin () = (Unix.getpwuid (getuid ())).Unix.pw_name

[1]: https://bitbucket.org/yminsky/ocaml-core/wiki/Home

I just tested your specific example, and it worked fine.

On Tue 20 Mar 2012 06:07:59 PM GMT, Ricardo Catalinas Jiménez wrote:
> 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