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TitleTypeSummaryLocation
SSH known_hosts Page When an SSH connection is being established, the server sends its public host key to the client and proves knowledge of the associated private host key. The OpenSSH client automatically stores the public host key of hosts that were previously accessed. These keys, called "known host keys", are stored in the known_hosts files.

The known_hosts files are plaintext files, with (generally) one known host information per line with the following information: the hostname(s) / IP address(es), the public host key type, the base64-encoded public host key, and an optional comment.

The remote hosts hostname and IP address can be either stored in clear-text or hashed. If the host information is hashed, it is possible to test wether a specific host is present in the known_hosts file, or to brute force the hashes to try to recover the associated hostname / IP addresses.
System-wide:
/etc/ssh/known_hosts

User scoped:
~/.ssh/known_hosts


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