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Top Forums UNIX for Advanced & Expert Users Max numer of connections per sshd Post 302152583 by craigp84 on Thursday 20th of December 2007 11:28:37 AM
Old 12-20-2007
You're possibly making connections at a rate which exceeds the number of new connections allowed at any one time.

SSHd will limit new connections, which have not yet completed authentication, in an attempt to avoid DOSing the whole machine if someone were to create thousands of ssh connections to your host.

So although the number of real connections is effectively unlimited AFAIK, there is a hard limit on the number of connections which are made, but are in the process of authenticating.

See the "MaxStartups" explaination in the sshd_config man page for full details.

Hope this helps,

-c
 

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listen(3XNET)					   X/Open Networking Services Library Functions 				     listen(3XNET)

NAME
listen - listen for socket connections and limit the queue of incoming connections SYNOPSIS
cc [ flag ... ] file ... -lxnet [ library ... ] #include <sys/socket.h> int listen(int socket, int backlog); DESCRIPTION
The listen() function marks a connection-mode socket, specified by the socket argument, as accepting connections, and limits the number of outstanding connections in the socket's listen queue to the value specified by the backlog argument. If listen() is called with a backlog argument value that is less than 0, the function sets the length of the socket's listen queue to 0. The implementation may include incomplete connections in the queue subject to the queue limit. The implementation may also increase the specified queue limit internally if it includes such incomplete connections in the queue subject to this limit. Implementations may limit the length of the socket's listen queue. If backlog exceeds the implementation-dependent maximum queue length, the length of the socket's listen queue will be set to the maximum supported value. The socket in use may require the process to have appropriate privileges to use the listen() function. RETURN VALUES
Upon successful completions, listen() returns 0. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The listen() function will fail if: EBADF The socket argument is not a valid file descriptor. EDESTADDRREQ The socket is not bound to a local address, and the protocol does not support listening on an unbound socket. EINVAL The socket is already connected. ENOTSOCK The socket argument does not refer to a socket. EOPNOTSUPP The socket protocol does not support listen(). The listen() function may fail if: EACCES The calling process does not have the appropriate privileges. EINVAL The socket has been shut down. ENOBUFS Insufficient resources are available in the system to complete the call. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
accept(3XNET), connect(3XNET), socket(3XNET), attributes(5), standards(5) SunOS 5.10 10 Jun 2002 listen(3XNET)
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