Re: ssh client hanging after authn for interactive sessions

On Sun, Jan 21, 2007 at 08:22:05PM -0800, David Anderson wrote:
> We're having some trouble on a linux ssh shell server. There are
> currently 300 or so account, and when any sizable number of these
> connect simultaneously, subsequent connections hang after
> authentication for any interactive session.
>
> Running non-interactive commands (say, `ls`) works fine, but running
> anything interactive (tried bash and zsh in this case) hangs the
> connection. When the connection is hanged, if the client is in verbose
> mode, I see keepalive packets being transmitted regularly, so the
> connection is there... Just not doing anything.
>
> This has been reported for many different clients, including putty on
> win32 and versions of openssh from 4.2 to 4.5 on linux, bsd and osx.
> The server itself has "OpenSSH_4.2p1, OpenSSL 0.9.7l 28 Sep 2006"
> installed.
>
> Has anyone encountered this before? We suspect we're running into some
> kind of resource limit, but ssh not explicitely failing or logging
> anything unusual is making this hard to debug. Follows a transcript of
> an openssh 4.2 trying to connect and get a shell:

I suspect that your server is running out of ptys.  Checking the server's
syslog should show errors if that's the case.

Depending on what vintage your Linux distro is you may need to mount
/dev/pts, add more pty device nodes in /dev or recompile the kernel with
more ptys.

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.