ssh-keyscan

 

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 SSH-KEYSCAN(1)          System General Commands Manual          SSH-KEYSCAN(1)
 
NAME
      ssh-keyscan - gather ssh public keys
 
SYNOPSIS
      ssh-keyscan [-t timeout] [-- | host | addrlist namelist] [-f files ...]
 
DESCRIPTION
      ssh-keyscan is a utility for gathering the public ssh host keys of a num­
      ber 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 pos­
      sible 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.  You do not need login access to the
      machines you are scanning, nor does the scanning process involve any
      encryption.
 
 SECURITY
      If you make an ssh_known_hosts file using ssh-keyscan without verifying
      the keys, you will be vulnerable to attacks.  On the other hand, if your
      security model allows such a risk, ssh-keyscan can help you detect tam­
      pered keyfiles or man in the middle attacks which have begun after you
      created your ssh_known_hosts file.
 
OPTIONS
      -t      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.
 
      -f      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.
 
 EXAMPLES
      Print the 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 -f ssh_hosts | sort -u - ssh_known_hosts | \
              diff ssh_known_hosts -
 
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: host-or-namelist bits exponent modulus
 
      /etc/ssh/ssh_known_hosts
 
 BUGS
      It generates "Connection closed by remote host" messages on the consoles
      of all the machines it scans.  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.
 
SEE ALSO
      ssh(1), sshd(8)
 
AUTHOR
      David Mazieres <dm@lcs.mit.edu>
 
 BSD                             January 1, 1996                            BSD

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