Request for help debugging screen problem

[Shaddy Baddah]

Hi Chris,

On 5/02/2010 3:34 PM, Christopher Faylor wrote:
> On Fri, Feb 05, 2010 at 03:08:43PM +0000, Shaddy Baddah wrote:
>> Hi,
>>
>> 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.
>> <snip>
>>>>> 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:
>> /cygdrive/z/shaddybaddah.name-projects/cygwin-master.git/winsup/cygwin/fhandler_tty.cc:556
>> 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.

As I expected, it has not made a difference (I commented out the 
cygserver conditional, and left the block) . I expected this as I 
originally had exactly the same symptoms with cygserver running, and 
sans cygserver.

Regards,
Shaddy