Installed on all Ubuntu VPS servers is DenyHosts, a log-based intrusion prevention security tool for SSH servers written in Python. It is intended to prevent brute force attacks on SSH servers by monitoring invalid login attempts in the authentication log and blocking the originating IP addresses.
If you have difficulties connecting to your VPS server via SSH from a specific IP, it may be blocked by Denyhosts. To check the list of blocked IP addresses, review the following file:
/etc/hosts.deny
If you see an IP in the list that you would like to allow SSH access from, use the steps below to remove the IP address from the list of blocked addresses:
To whitelist an IP address so it is not blocked by Denyhosts, please add the IP to the following file:
/etc/hosts.allow
For example:
sshd: 127.0.0.1
For more information, please visit http://denyhosts.sourceforge.net/.
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