strange behaviour with ssh / stdin

Roumen Petrov openssh at
Wed Oct 15 19:12:50 EST 2003

Might is linux kernel(?), not ssh(!) problem.
As Laurent show ".../fd/0 -> socket:[27105]", i.e. on linux we have 
broken symbolic link - cat ".../fd/0" cannot found 
".../fd/socket:[27105]" file.
It is strange that cat without arguments work on linux.

Darren Tucker wrote:

>Damien Miller wrote:
>>On Mon, 2003-10-13 at 19:56, Laurent Bartholdi wrote:
>>>i noted the following strange behaviour using ssh and linux. this is
>>>probably a low-priority bug:
>>># ssh -V
>>>OpenSSH_3.6.1p2, SSH protocols 1.5/2.0, OpenSSL 0x0090701f
>>># uname -a
>>>Linux funnyfarm 2.4.21-20.1.2024.2.1.nptl #1 Fri Jul 11 06:04:52 EDT 2003 i686 i686 i386 GNU/Linux
>>># echo Hello | ssh frodo 'cat'
>>># echo Hello | ssh frodo 'cat /proc/self/fd/0'
>>>cat: /proc/self/fd/0: No such device or address
>>># ssh frodo 'ls -l /proc/self/fd/0'
>>>lrwx------    1 root     root           64 Oct 13 18:51 /proc/self/fd/0 -> socket:[27105]
>>This is probably some weird Linux race condition. I can't imagine
>>anything that ssh could do that would cause this.
>>Does /dev/stdin or /dev/fd/0 work? These are often aliases for the same
>On my RH8 box they're all symlinks to the controlling tty if it has one or
>to some kind of socket descriptor if not (as you noted).  The problem
>appears to be Linux-specific.
>$  uname -sr; ls -l /dev/stdin /dev/fd/0 /proc/self/fd/0
>Linux 2.4.20-20.8
>lrwx------    1 dtucker  dtucker        64 Oct 14 22:06 /dev/fd/0 ->
>lrwxrwxrwx    1 root     root           17 Mar 31  2003 /dev/stdin ->
>lrwx------    1 dtucker  dtucker        64 Oct 14 22:06 /proc/self/fd/0 ->
>In contrast, on Solaris, /dev/fd/0 is a character special device, and your
>example works as expected:
>$ uname -sr; ls -l /dev/fd/0 /dev/stdin
>SunOS 5.8
>crw-rw-rw-   1 root     root     247,  0 Oct 14 22:09 /dev/fd/0
>lrwxrwxrwx   1 root     root           6 Apr  2  2002 /dev/stdin -> ./fd/0
>$ echo Hello | ssh localhost "cat /dev/fd/0"
>I remember reading an explanation about this someplace but I don't
>remember the details and I've been unable to locate it again.

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