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Linux 2.6 - man page for ssh-keyscan (linux section 1)

SSH-KEYSCAN(1)			   BSD General Commands 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 sup-
	     plied 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.

BSD					 August 21, 2018				      BSD


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