Help request: problems with a 5.1 server and large numbers of ssh users.

Len Sassaman rabbi at
Thu Nov 20 16:57:11 PST 2003

> Hmm.  Well, it certainly sounds like a resource limit to me, 
> especially if
> it's a nice round number like "150" or "300".  However, I'm also 
> having a
> bit of trouble seeing, off the top of my head, which limit it might be.
> It sounds like you've got the ones I would think of.  A quick skim of
> sshd.c suggests that it is pretty careful to document various failure
> modes in debugging output.  There are one or two failures where it does
> not log, and they include the call to pipe() in the server loop -- if 
> that
> fails, it bails without an error, which is a little surprising.  Could 
> you
> post server debug output for the first connection to the server that
> fails?  This would let us "see how far it got"...  In particular, 
> whether
> it did spawn a child process, etc.

I have never gotten this to fail when sshd is running in debug mode 
(i.e., sshd -ddd). However, given that it doesn't fork when run with 
-d, that still doesn't tell us too much.

When I set LogLevel DEBUG3, this is as much info as I am given in the 

Nov 20 16:39:19 clyde sshd[63993]: Failed none for rabbi from 
port 62701 ssh2

And this is the debug output for the connection, as seen from the 

bash-2.05b# ssh -vvv -l rabbi localhost
OpenSSH_3.6.1p2, SSH protocols 1.5/2.0, OpenSSL 0x0090701f
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Rhosts Authentication disabled, originating port will not be 
debug2: ssh_connect: needpriv 0
debug1: Connecting to localhost [::1] port 22.
socket: Protocol not supported
debug1: Connecting to localhost [] port 22.
debug1: Connection established.
debug1: identity file /root/.ssh/identity type -1
debug1: identity file /root/.ssh/id_rsa type -1
debug1: identity file /root/.ssh/id_dsa type -1
ssh_exchange_identification: Connection closed by remote host

This can't be a system-wide process related resource issue, I don't 
think, because once a user connects and authenticates, there are no 
problems of note. I'm leaning toward a socket related limit or 
user-level limit. However, since sysctl tells me:

kern.ipc.maxsockbuf: 262144
kern.ipc.somaxconn: 16384
kern.ipc.numopensockets: 2201
kern.ipc.maxsockets: 49312

I tend to not believe the former, and why the latter would be occurring 
escapes me as well. 

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