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+SSH-KEYSCAN(1)              General Commands Manual             SSH-KEYSCAN(1)
+
+NAME
+     ssh-keyscan M-bM-^@M-^S gather SSH public keys
+
+SYNOPSIS
+     ssh-keyscan [-46cDHv] [-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, the format of which is documented in sshd(8).
+     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 sshd(8).  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      Force ssh-keyscan to use IPv4 addresses only.
+
+     -6      Force ssh-keyscan to use IPv6 addresses only.
+
+     -c      Request certificates from target hosts instead of plain keys.
+
+     -D      Print keys found as SSHFP DNS records.  The default is to print
+             keys in a format usable as a ssh(1) known_hosts file.
+
+     -f file
+             Read hosts or M-bM-^@M-^\addrlist namelistM-bM-^@M-^] pairs from file, one per line.
+             If M-bM-^@M-^X-M-bM-^@M-^Y is supplied instead of a filename, ssh-keyscan will read
+             from the standard input.  Input is expected in the 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
+
+     -H      Hash all hostnames and addresses in the output.  Hashed names may
+             be used normally by ssh(1) and sshd(8), but they do not reveal
+             identifying information should the file's contents be disclosed.
+
+     -p port
+             Connect to port 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, the connection is
+             closed and the host in question considered unavailable.  The
+             default is 5 seconds.
+
+     -t type
+             Specify the type of the key to fetch from the scanned hosts.  The
+             possible values are M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^].
+             Multiple values may be specified by separating them with commas.
+             The default is to fetch M-bM-^@M-^\rsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], and M-bM-^@M-^\ed25519M-bM-^@M-^] keys.
+
+     -v      Verbose mode: print debugging messages about progress.
+
+     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
+     /etc/ssh/ssh_known_hosts
+
+EXAMPLES
+     Print the RSA host key for machine hostname:
+
+           $ ssh-keyscan -t rsa 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,ed25519 -f ssh_hosts | \
+                   sort -u - ssh_known_hosts | diff ssh_known_hosts -
+
+SEE ALSO
+     ssh(1), sshd(8)
+
+     Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints, RFC
+     4255, 2006.
+
+AUTHORS
+     David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
+     Davison <wayned@users.sourceforge.net> added support for protocol version
+     2.
+
+OpenBSD 6.6                      March 5, 2018                     OpenBSD 6.6