libssh2 is hanging during a file transfert

Micka mickamusset at
Tue Jul 7 23:19:29 AEST 2020

I don't see a problem, my MTU is at the default value = 1500,

but when I look at the trace from libssh2,

packet type 4 received,  => SSH_MSG_DEBUG
packet type 91 received,  => SSH_MSG_CHANNEL_OPEN_CONFIRMATION
packet type 93 received, => SSH_MSG_CHANNEL_WINDOW_ADJUST
packet type 99 received, => SSH_MSG_CHANNEL_SUCCESS
packet type 98 received, => SSH_MSG_CHANNEL_REQUEST
packet type 96 received, => SSH_MSG_CHANNEL_EOF
packet type 97 received, => SSH_MSG_CHANNEL_CLOSE ==> why ?

and in the log sshd, I've some strange line :

Jul  7 11:52:16 TOTO sshd[19553]: debug1: session_exit_message: release
channel 0
Jul  7 11:52:16 TOTO sshd[19553]: debug2: channel 0: write failed

On Tue, Jul 7, 2020 at 1:57 PM Brian Candler <b.candler at> wrote:

> My first thought is it could be an MTU problem.
> Try running tcpdump at both ends - you should see the same packets (*).
> If you find one side sends a maximum-sized packet, but the other side
> receives nothing, then that's very likely the issue.
> If you don't have access to the far side, then reduce the TCP MSS on
> your side and try again.  (Or at worst, just reduce the MTU on your
> interface).  At least you'll know if that's the problem or not.
> Regards,
> Brian.
> (*) Maybe multiple packets will appear as one packet, if your NIC
> reassembles TCP segments.  Turning off TCP offload on your NIC can
> sometimes be worth trying too.

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