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From: Ken Brown <kbrown AT cornell DOT edu>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Re: ssh-agent doesn't die
Date: Sun, 29 Sep 2019 20:05:44 +0000
Message-ID: <185c5774-dd8b-5488-b818-4cec5a24bf2d@cornell.edu>
References: <319e26c0-32f0-40b7-2137-c7de170a3486 AT rl DOT ac DOT uk> <5b225738-c2d7-fbfe-48a7-8c2a38c3398c AT cornell DOT edu> <0ccd17b6-c22a-1a18-9409-1ebcfae60868 AT huarp DOT harvard DOT edu> <9f7a14bb-f81b-c566-bb84-8da7fc6d0fad AT cornell DOT edu>
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On 9/27/2019 10:12 AM, Ken Brown wrote:
> On 9/27/2019 9:37 AM, Norton Allen wrote:
>> On 9/26/2019 10:50 PM, Ken Brown wrote:
>>>
>>>> As a simple test example, consider:
>>>>
>>>> /bin/ssh-agent /bin/sleep 10
>>>>
>>>> While the sleep is still running, ps shows:
>>>>
>>>>  =A0 =A0=A0=A0=A0=A0 PID=A0=A0=A0 PPID=A0=A0=A0 PGID=A0=A0=A0=A0 WINPI=
D=A0=A0 TTY=A0=A0=A0=A0=A0=A0=A0=A0 UID=A0=A0=A0 STIME COMMAND
>>>>  =A0 =A0=A0=A0=A0 1694=A0=A0=A0 1693=A0=A0=A0 1694=A0=A0=A0=A0=A0=A0 1=
576=A0 ?=A0=A0=A0=A0=A0=A0=A0=A0=A0 22534 00:01:10
>>>> /usr/bin/ssh-agent
>>>>  =A0 =A0=A0=A0=A0 1653=A0=A0=A0=A0=A0=A0 1=A0=A0=A0 1653=A0=A0=A0=A0=
=A0 11740=A0 cons1=A0=A0=A0=A0=A0 22534 00:00:37 /usr/bin/bash
>>>>  =A0 =A0=A0=A0=A0 1693=A0=A0=A0 1653=A0=A0=A0 1693=A0=A0=A0=A0=A0=A0 1=
552=A0 cons1=A0=A0=A0=A0=A0 22534 00:01:10 /usr/bin/sleep
>>>>
>>>> One oddity is that ssh-agent is listed as a subprocess of sleep
>>> ...but this isn't a bug.=A0 ssh-agent forks, and then the parent execs =
the command.
>>
>> With the salient difference presumably being that the exec is done in th=
e parent
>> instead of the child as usual?
>=20
> Yes.  The idea is that 'ssh-agent command' should be more-or-less equival=
ent to
> running 'command', with ssh-agent running as a subprocess.
>=20
> The ssh-agent subprocess periodically checks to see if its parent is still
> alive, and it exits when the parent has died.  Someone should figure out =
why
> this is not working on Cygwin.

As an aid to someone who might want to debug this (probably Corinna when sh=
e=20
returns), I've created a test program agent.c (attached) that simulates the=
=20
relevant part of ssh-agent:

1. It forks a subprocess that periodically checks to see if its parent has =
died,=20
and then exits.

2. The parent execs "/usr/bin/sleep 1".

As with ssh-agent, the subprocess never detects that the parent has died, a=
nd so=20
it never exits.

Running this program under strace shows the following error in the pinfo=20
constructor:

pinfo::pinfo: couldn't duplicate parent rd_proc_pipe handle 0x1BC for forke=
d=20
child 1666 after exec, Win32 error 5

[Win32 error 5 is ERROR_ACCESS_DENIED.]

I assume this is the source of the problem, but I don't understand the code=
 well=20
enough to know why.  I also don't know why the call to DuplicateHandle fail=
s.

Ken

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