Request for help debugging screen problem

Christopher Faylor
Fri Feb 5 15:34:00 GMT 2010

On Fri, Feb 05, 2010 at 03:08:43PM +0000, Shaddy Baddah wrote:
>On 5/02/2010 2:35 PM, Christopher Faylor wrote:
>> On Fri, Feb 05, 2010 at 02:46:48PM +0100, Corinna Vinschen wrote:
>>> On Feb  5 10:42, Shaddy Baddah wrote:
>>>> I'm trying to debug a problem with screen, rather than publish a bug
>>>> report. I can do that as well if someone requests it, no problem.
>>>> Any help would be greatly appreciated.
>>> Can yopu expolain this in more detail, please?  What error codes
>>> are returned, and how do you trigger the effect?
>> Also, unless you have CYGWIN=server set, this code should not be used
>> by the pty handler so I don't know why you're looking here.
>The answer to Corinna's question may answer that. The situation is that 
>I cannot reattach to a screen session from when logged in via ssh  on a 
>Vista or Windows 7 install(which has CYGWIN=server set, right? To be 
>honest, I have lost track of my tinkering with involving cygserver 
>(which wasn't setup when the problem initially presented)). The same 
>sessions can be attached by the same user using a desktop mintty 
>session. And in this particular case, the user is non-Administrator.
>  The message gets clobbered by the screen clear, but if you use strace, 
>the error message seen is:
>   185   26254 [main] screen 4812 C:\software\cygwin\bin\screen.exe: *** 
>fatal error - couldn't initialize fd 0 for /dev/tty2
>The issue is almost definitely related to the privilege model on these 
>OSes, as as I expected, XP doesn't present with the same problem. It 
>also does not present if I ssh into the unlocked Administrator account. 
>It of course does present if logged into a Administrators grouped user 
>account other than the standard Administrator user.
>The strace revealed that the int fhandler_tty_slave::open(int, mode_t) 
>called was returning EACCES in this way:
>    44   25864 [main] screen 4812 fhandler_tty_slave::open: cannot dup 
>handles via server. using old method.
>   116   25980 [main] screen 4812 fhandler_tty_slave::open: can't open 
>tty (2) handle process 3748
>    33   26013 [main] screen 4812 seterrno_from_win_error: 
>windows error 5
>    29   26042 [main] screen 4812 geterrno_from_win_error: windows error 
>5 == errno 13
>    27   26069 [main] screen 4812 __set_errno: void 
>seterrno_from_win_error(const char*, int, DWORD):319 val 13
>   185   26254 [main] screen 4812 C:\software\cygwin\bin\screen.exe: *** 
>fatal error - couldn't initialize fd 0 for /dev/tty2
>I was hoping to detect what the differences in privileges/tokens??? 
>between the regular desktop sesssion, and the ssh session are. In that 
>way, I was hoping to understand why ReadFile was denying access, and see 
>if I could tweak some of the named pipe creation flags. This is all very 
>uninformed, but I was hoping to learn along the way.
>I can attach the strace log on request.

Not yet.  Since this is cygwin-developers, not cygwin, the next step,
given that we're theorizing a problem with cygserver, would be to
rebuild the dll with the call to cygserver commented out to see if that
fixes anything.


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