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:
>>>>
>>>> PID PPID PGID WINPID TTY UID STIME COMMAND
>>>> 1694 1693 1694 1576 ? 22534 00:01:10
>>>> /usr/bin/ssh-agent
>>>> 1653 1 1653 11740 cons1 22534 00:00:37
>>>> /usr/bin/bash
>>>> 1693 1653 1693 1552 cons1 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. ssh-agent forks, and then the parent execs the
>>> command.
>>
>> With the salient difference presumably being that the exec is done in the
>> parent
>> instead of the child as usual?
>
> Yes. The idea is that 'ssh-agent command' should be more-or-less equivalent
> to
> running 'command', with ssh-agent running as a subprocess.
>
> 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 she
returns), I've created a test program agent.c (attached) that simulates the
relevant part of ssh-agent:
1. It forks a subprocess that periodically checks to see if its parent has
died,
and then exits.
2. The parent execs "/usr/bin/sleep 1".
As with ssh-agent, the subprocess never detects that the parent has died, and
so
it never exits.
Running this program under strace shows the following error in the pinfo
constructor:
pinfo::pinfo: couldn't duplicate parent rd_proc_pipe handle 0x1BC for forked
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
enough to know why. I also don't know why the call to DuplicateHandle fails.
Ken
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
pid_t parent_pid = -1;
void
check_parent_exists ()
{
if (parent_pid != -1 && getppid () != parent_pid)
{
printf ("Parent has died - agent exiting.\n");
exit (2);
}
}
int
main ()
{
char *cmd[] = { "/usr/bin/sleep", "1", NULL };
parent_pid = getpid ();
pid_t pid = fork ();
switch (pid)
{
case -1:
perror ("fork");
exit (1);
case 0:
/* child */
while (1)
{
check_parent_exists ();
sleep (1);
}
break;
default:
/* parent */
execvp (cmd[0], cmd);
perror ("execvp");
exit (1);
}
}
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
