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+SSH-KEYSCAN(1)             OpenBSD Reference Manual             SSH-KEYSCAN(1)
+
+NAME
+     ssh-keyscan - gather ssh public keys
+
+SYNOPSIS
+     ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type]
+                 [host | addrlist namelist] ...
+
+DESCRIPTION
+     ssh-keyscan is a utility for gathering the public ssh host keys of a
+     number of hosts.  It was designed to aid in building and verifying
+     ssh_known_hosts files.  ssh-keyscan provides a minimal interface suitable
+     for use by shell and perl scripts.
+
+     ssh-keyscan uses non-blocking socket I/O to contact as many hosts as
+     possible in parallel, so it is very efficient.  The keys from a domain of
+     1,000 hosts can be collected in tens of seconds, even when some of those
+     hosts are down or do not run ssh.  For scanning, one does not need login
+     access to the machines that are being scanned, nor does the scanning
+     process involve any encryption.
+
+     The options are as follows:
+
+     -4      Forces ssh-keyscan to use IPv4 addresses only.
+
+     -6      Forces ssh-keyscan to use IPv6 addresses only.
+
+     -f file
+             Read hosts or addrlist namelist pairs from this file, one per
+             line.  If - is supplied instead of a filename, ssh-keyscan will
+             read hosts or addrlist namelist pairs from the standard input.
+
+     -H      Hash all hostnames and addresses in the output.  Hashed names may
+             be used normally by ssh and sshd, but they do not reveal
+             identifying information should the file's contents be disclosed.
+
+     -p port
+             Port to connect to on the remote host.
+
+     -T timeout
+             Set the timeout for connection attempts.  If timeout seconds have
+             elapsed since a connection was initiated to a host or since the
+             last time anything was read from that host, then the connection
+             is closed and the host in question considered unavailable.
+             Default is 5 seconds.
+
+     -t type
+             Specifies the type of the key to fetch from the scanned hosts.
+             The possible values are ``rsa1'' for protocol version 1 and
+             ``dsa'', ``ecdsa'' or ``rsa'' for protocol version 2.  Multiple
+             values may be specified by separating them with commas.  The
+             default is ``rsa''.
+
+     -v      Verbose mode.  Causes ssh-keyscan to print debugging messages
+             about its progress.
+
+SECURITY
+     If an ssh_known_hosts file is constructed using ssh-keyscan without
+     verifying the keys, users will be vulnerable to man in the middle
+     attacks.  On the other hand, if the security model allows such a risk,
+     ssh-keyscan can help in the detection of tampered keyfiles or man in the
+     middle attacks which have begun after the ssh_known_hosts file was
+     created.
+
+FILES
+     Input format:
+
+     1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
+
+     Output format for rsa1 keys:
+
+     host-or-namelist bits exponent modulus
+
+     Output format for rsa, dsa and ecdsa keys:
+
+     host-or-namelist keytype base64-encoded-key
+
+     Where keytype is either ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'',
+     ``ecdsa-sha2-nistp521'', ``ssh-dss'' or ``ssh-rsa''.
+
+     /etc/ssh/ssh_known_hosts
+
+EXAMPLES
+     Print the rsa host key for machine hostname:
+
+     $ ssh-keyscan hostname
+
+     Find all hosts from the file ssh_hosts which have new or different keys
+     from those in the sorted file ssh_known_hosts:
+
+     $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \
+             sort -u - ssh_known_hosts | diff ssh_known_hosts -
+
+SEE ALSO
+     ssh(1), sshd(8)
+
+AUTHORS
+     David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
+     Davison <wayned@users.sourceforge.net> added support for protocol version
+     2.
+
+BUGS
+     It generates "Connection closed by remote host" messages on the consoles
+     of all the machines it scans if the server is older than version 2.9.
+     This is because it opens a connection to the ssh port, reads the public
+     key, and drops the connection as soon as it gets the key.
+
+OpenBSD 5.0                     August 31, 2010                    OpenBSD 5.0