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Date: Mon, 31 May 2010 12:39:30 +0100
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Subject: Re: "can't create master tty" errors
From: Andy Koppe <andy DOT koppe AT gmail DOT com>
To: Cesar Crusius <cesar AT cariden DOT com>, cygwin AT cygwin DOT com
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On 9 March 2010 21:50, Andy Koppe wrote:
> Cesar Crusius:
>> I am using Cygwin and SSH to do automated remote builds using Visual
>> C++. It works for a few days, but invariably things start failing with
>> messages like these (this one from a build log):
>>
>> Makefile:9: MakePID: 5964
>> =C2=A0 =C2=A0 =C2=A01 [main] env 2748 C:\cygwin\bin\env.exe: *** fatal e=
rror - can't create master tty
>
> The number of tty devices is limited, so the first thing to check is
> whether your build system simply leaves too many sessions open, by
> checking the output of 'ps'.
>
> If not, it might be to do with the following. If you open a couple of
> terminals, they're assigned =C2=A0tty0 and tty1. If you then close tty1 a=
nd
> open another terminal, that again becomes tty1. But if you close tty0,
> and open yet another one, that becomes tty2 rather than tty0.
>
> That appears to be the general rule: a new terminal gets the next ID
> above the current highest one. This means, however, that if opening
> and closing of terminal sessions is interleaved in certain ways,
> Cygwin might eventually run out of terminal IDs, even if only few of
> them are actually used. High numbers in the TTY column of the 'ps'
> output would point to that.
>
> Cgf, am I talking rubbish here?

For the record: I was. What I observed there was due to a bug in
mintty: a new mintty session spawned using Alt+F2 inherited the pty
file descriptor from its parent, and by extension, also the
descriptors from its previous ancestors. Due to that, a pty device
wasn't released until the session that actually used it and all the
sessions spawned from that were closed. Fixed for mintty-0.7.

So pty numbers are reused just fine, and I can't help with the OP's issue.

Andy

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