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      1 SSH-KEYSCAN(1)              General Commands Manual             SSH-KEYSCAN(1)
      2 
      3 NAME
      4      ssh-keyscan M-bM-^@M-^S gather ssh public keys
      5 
      6 SYNOPSIS
      7      ssh-keyscan [-46cHv] [-f file] [-p port] [-T timeout] [-t type]
      8                  [host | addrlist namelist] ...
      9 
     10 DESCRIPTION
     11      ssh-keyscan is a utility for gathering the public ssh host keys of a
     12      number of hosts.  It was designed to aid in building and verifying
     13      ssh_known_hosts files.  ssh-keyscan provides a minimal interface suitable
     14      for use by shell and perl scripts.
     15 
     16      ssh-keyscan uses non-blocking socket I/O to contact as many hosts as
     17      possible in parallel, so it is very efficient.  The keys from a domain of
     18      1,000 hosts can be collected in tens of seconds, even when some of those
     19      hosts are down or do not run ssh.  For scanning, one does not need login
     20      access to the machines that are being scanned, nor does the scanning
     21      process involve any encryption.
     22 
     23      The options are as follows:
     24 
     25      -4      Forces ssh-keyscan to use IPv4 addresses only.
     26 
     27      -6      Forces ssh-keyscan to use IPv6 addresses only.
     28 
     29      -c      Request certificates from target hosts instead of plain keys.
     30 
     31      -f file
     32              Read hosts or M-bM-^@M-^\addrlist namelistM-bM-^@M-^] pairs from file, one per line.
     33              If - is supplied instead of a filename, ssh-keyscan will read
     34              hosts or M-bM-^@M-^\addrlist namelistM-bM-^@M-^] pairs from the standard input.
     35 
     36      -H      Hash all hostnames and addresses in the output.  Hashed names may
     37              be used normally by ssh and sshd, but they do not reveal
     38              identifying information should the file's contents be disclosed.
     39 
     40      -p port
     41              Port to connect to on the remote host.
     42 
     43      -T timeout
     44              Set the timeout for connection attempts.  If timeout seconds have
     45              elapsed since a connection was initiated to a host or since the
     46              last time anything was read from that host, then the connection
     47              is closed and the host in question considered unavailable.
     48              Default is 5 seconds.
     49 
     50      -t type
     51              Specifies the type of the key to fetch from the scanned hosts.
     52              The possible values are M-bM-^@M-^\rsa1M-bM-^@M-^] for protocol version 1 and M-bM-^@M-^\dsaM-bM-^@M-^],
     53              M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^] for protocol version 2.  Multiple
     54              values may be specified by separating them with commas.  The
     55              default is to fetch M-bM-^@M-^\rsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], and M-bM-^@M-^\ed25519M-bM-^@M-^] keys.
     56 
     57      -v      Verbose mode.  Causes ssh-keyscan to print debugging messages
     58              about its progress.
     59 
     60 SECURITY
     61      If an ssh_known_hosts file is constructed using ssh-keyscan without
     62      verifying the keys, users will be vulnerable to man in the middle
     63      attacks.  On the other hand, if the security model allows such a risk,
     64      ssh-keyscan can help in the detection of tampered keyfiles or man in the
     65      middle attacks which have begun after the ssh_known_hosts file was
     66      created.
     67 
     68 FILES
     69      Input format:
     70 
     71      1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
     72 
     73      Output format for RSA1 keys:
     74 
     75      host-or-namelist bits exponent modulus
     76 
     77      Output format for RSA, DSA, ECDSA, and Ed25519 keys:
     78 
     79      host-or-namelist keytype base64-encoded-key
     80 
     81      Where keytype is either M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^], M-bM-^@M-^\ecdsa-sha2-nistp384M-bM-^@M-^],
     82      M-bM-^@M-^\ecdsa-sha2-nistp521M-bM-^@M-^], M-bM-^@M-^\ssh-ed25519M-bM-^@M-^], M-bM-^@M-^\ssh-dssM-bM-^@M-^] or M-bM-^@M-^\ssh-rsaM-bM-^@M-^].
     83 
     84      /etc/ssh/ssh_known_hosts
     85 
     86 EXAMPLES
     87      Print the rsa host key for machine hostname:
     88 
     89      $ ssh-keyscan hostname
     90 
     91      Find all hosts from the file ssh_hosts which have new or different keys
     92      from those in the sorted file ssh_known_hosts:
     93 
     94      $ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \
     95              sort -u - ssh_known_hosts | diff ssh_known_hosts -
     96 
     97 SEE ALSO
     98      ssh(1), sshd(8)
     99 
    100 AUTHORS
    101      David Mazieres <dm (a] lcs.mit.edu> wrote the initial version, and Wayne
    102      Davison <wayned (a] users.sourceforge.net> added support for protocol version
    103      2.
    104 
    105 BUGS
    106      It generates "Connection closed by remote host" messages on the consoles
    107      of all the machines it scans if the server is older than version 2.9.
    108      This is because it opens a connection to the ssh port, reads the public
    109      key, and drops the connection as soon as it gets the key.
    110 
    111 OpenBSD 6.0                    November 8, 2015                    OpenBSD 6.0
    112