Bug 2964

Summary:	OpenSSH for Windows often hangs if no data sent over the connection
Product:	Portable OpenSSH	Reporter:	leese
Component:	ssh	Assignee:	Assigned to nobody <unassigned-bugs>
Status:	CLOSED INVALID
Severity:	normal	CC:	djm, jjelen
Priority:	P5
Version:	7.9p1
Hardware:	Other
OS:	Windows 10

Description leese 2019-02-06 08:46:50 AEDT

This was reproduced on both 7.7p1 and 7.9p1, while ssh-ing from a Windows machine to a Linux machine. For a simple repro I'm using the bash commands `echo ""` (should output a single newline) and `echo -n ""` (should output nothing and immediately exit successfully; I've also used /bin/true which is equivalent.)

> ssh user@host -- echo ""

Reliably returns right away as expected.

> ssh user@host -tt -- echo ""

Reliably returns right away as expected.

> ssh user@host -- echo -n ""

Seems to hang, but if you press a key it returns.

> ssh user@host -tt -- echo -n ""

Sometimes it works, sometimes it hangs. When it hangs it will be unresponsive to input, including ^C. You need to kill it in task manager. A wireshark trace shows that the server sent the TCP FIN packet, but the client is still holding open the connection.

> ssh user@host -tt -v -- echo -n ""

Turning on verbose output seems to make it work reliably.

Not sure to what extent network latency affects this but my ping time is 11ms.

Comment 1 Jakub Jelen 2019-02-06 20:24:46 AEDT

This could be related to the bug #2071 which is there for ages and has similar symptoms also on Linux platforms. You can try the patch I proposed there few years back if it solves also your problem.

Comment 2 Damien Miller 2019-02-08 14:56:19 AEDT

What client are you using? Are you using the Microsoft ssh client or the Cygwin one?

Comment 3 leese 2019-02-09 03:42:10 AEDT

I'm using the Microsoft client. I filed a bug with them:

https://github.com/PowerShell/Win32-OpenSSH/issues/1338

Comment 4 Damien Miller 2021-04-23 14:58:14 AEST

closing resolved bugs as of 8.6p1 release