Mosh regression between 10.x and 11-stable
cgull+l-freebsd-current at glup.org
Wed Aug 10 18:46:57 UTC 2016
On 8/10/16 4:18 AM, Peter Jeremy wrote:
> I recently updated one of my VPS hosts from 10.3-RELEASE-p5 to 11.0-BETA4
> r303811 and mosh to that host from my Linux laptop stopped working. All
> I get on the laptop is:
> $ mosh remotehost
> Connection to remotehost closed.
> /usr/bin/mosh: Did not find mosh server startup message.
> I've tried rebuilding mosh (and all dependencies) on the host to no avail.
I'm a mosh maintainer. mosh 1.2.5 (from ports) and mosh master (just
last night tagged as 1.2.6, alas) work fine for me on my two 11.0-BETA4
systems, one local and one remote.
> This isn't the DSA change that's been discussed elsewhere: I can SSH from my
> laptop to the host without problem. I can also manually invoke mosh-client
> and mosh-server and it works. Unfortunately, mosh has no provision for
> debugging. I've tried hacking the mosh perl script to make it more verbose
> and that shows that:
> 1) the "MOSH CONNECT" message isn't making it out of the local ssh process.
Do you know if the message is getting out of mosh-server? into sshd?
Do you know if mosh-server is actually running? (It will log utmp
entries on startup.)
Mosh's debugging/logging isn't very good, but 'mosh-server new -v 2>
logfile' does produce some useful info (mostly logging of network traffic).
> 2) it's racy because I can get it from "always fails" to "sometimes works".
How do you get it there?
> My suspicion is that something has changed in either sshd or TCP that
> is resulting in the connection going away before the stdout from the
> remote mosh-server makes it out from the local ssh process.
mosh does 'ssh -t' and uses ptys. That's another potential point the
message could get dropped.
> I've looked at tcpdump's of both successful and failed SSH sessions
> but don't see anything obviously different (encryption makes it
> difficult to decode the session).
> Has anyone else seen this behaviour or have any ideas what might be
> causing it?
Common suspects include issues with shell login/invocation of mosh (are
you making sure it's reachable in /usr/local/bin with $PATH or
'--server=/usr/local/bin/mosh'? are your login shell and its login
On Linux we've had issues with ecryptfs and systemd breaking mosh-server
when the ssh session ends, but I don't think that applies here.
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