SSH Frequently Asked Questions
My SSH client connects, but the server seems to immediately close the connection. I get "connection closed" or "connection lost," or with OpenSSH:
ssh_exchange_identification: Connection closed by remote host
This message means that the client got a TCP connection to the server, but the server immediately closed it before the SSH protocol could get started (the
ssh_exchange_identification routine implements the
version string exchange, the initial step of the protocol).
This usually happens because of a libwrap setting which prohibits the connection. Check the server log; if this is the problem, you will see messages like these:
- SSH1, OpenSSH
sshd1[15092]: refused connect from 192.168.10.1 - SSH2
sshd2[15085]: Denied connection from by 192.168.10.1 tcp wrappers.
/etc/hosts.{allow,deny} on the
server host allow connection to the SSH daemon. An entry like this, for
example, will allow connections to sshd from any source address:
sshd sshd1 sshd2 : ALL : ALLOW
The name on the left must be the argv[0] value of the running daemon, so
if you've invoked sshd under another name, you'll need to use that. Also,
the rules are order-dependent, so the rule just given might not work,
depending on the other rules and their relative placement. See the
hosts_access(5) man page for details on the libwrap rule
syntax and semantics.