9.5.6 Troubleshooting SSH
If you have problems, check the permissions of configuration files and run
ssh with the "-v" option.
Use the "-P" option if you are root and have trouble
with a firewall; this avoids the use of server ports 1–1023.
If ssh connections to a remote site suddenly stop working, it may
be the result of tinkering by the sysadmin, most likely a change in
host_key during system maintenance. After making sure this is the
case and nobody is trying to fake the remote host by some clever hack, one can
regain a connection by removing the host_key entry from
$HOME/.ssh/known_hosts on the local machine.
