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Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.4.2.2

1.4.2.2 ! jason       1: .\"    $OpenBSD: ssh-keyscan.1,v 1.4 2001/03/01 03:38:33 deraadt Exp $
        !             2: .\"
        !             3: .\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
        !             4: .\"
        !             5: .\" Modification and redistribution in source and binary forms is
        !             6: .\" permitted provided that due credit is given to the author and the
        !             7: .\" OpenBSD project (for instance by leaving this copyright notice
        !             8: .\" intact).
1.4       deraadt     9: .\"
1.1       markus     10: .Dd January 1, 1996
1.4.2.2 ! jason      11: .Dt SSH-KEYSCAN 1
1.1       markus     12: .Os
                     13: .Sh NAME
                     14: .Nm ssh-keyscan
                     15: .Nd gather ssh public keys
                     16: .Sh SYNOPSIS
                     17: .Nm ssh-keyscan
                     18: .Op Fl t Ar timeout
                     19: .Op Ar -- | host | addrlist namelist
                     20: .Op Fl f Ar files ...
                     21: .Sh DESCRIPTION
                     22: .Nm
                     23: is a utility for gathering the public ssh host keys of a number of
                     24: hosts.  It was designed to aid in building and verifying
                     25: .Pa ssh_known_hosts
                     26: files.
                     27: .Nm
                     28: provides a minimal interface suitable for use by shell and perl
                     29: scripts.
                     30: .Pp
                     31: .Nm
                     32: uses non-blocking socket I/O to contact as many hosts as possible in
                     33: parallel, so it is very efficient.  The keys from a domain of 1,000
                     34: hosts can be collected in tens of seconds, even when some of those
                     35: hosts are down or do not run ssh.  You do not need login access to the
                     36: machines you are scanning, nor does does the scanning process involve
                     37: any encryption.
                     38: .Sh SECURITY
                     39: If you make an ssh_known_hosts file using
                     40: .Nm
                     41: without verifying the keys, you will be vulnerable to
                     42: .I man in the middle
                     43: attacks.
                     44: On the other hand, if your security model allows such a risk,
                     45: .Nm
                     46: can help you detect tampered keyfiles or man in the middle attacks which
                     47: have begun after you created your ssh_known_hosts file.
                     48: .Sh OPTIONS
                     49: .Bl -tag -width Ds
                     50: .It Fl t
                     51: Set the timeout for connection attempts.  If
                     52: .Pa timeout
                     53: seconds have elapsed since a connection was initiated to a host or since the
                     54: last time anything was read from that host, then the connection is
                     55: closed and the host in question considered unavailable.  Default is 5
                     56: seconds.
                     57: .It Fl f
                     58: Read hosts or
                     59: .Pa addrlist namelist
                     60: pairs from this file, one per line.
                     61: If
                     62: .Pa -
                     63: is supplied instead of a filename,
                     64: .Nm
                     65: will read hosts or
                     66: .Pa addrlist namelist
                     67: pairs from the standard input.
1.2       itojun     68: .El
1.1       markus     69: .Sh EXAMPLES
                     70: .Pp
                     71: Print the host key for machine
                     72: .Pa hostname :
                     73: .Bd -literal
                     74: ssh-keyscan hostname
                     75: .Ed
                     76: .Pp
                     77: Find all hosts from the file
                     78: .Pa ssh_hosts
                     79: which have new or different keys from those in the sorted file
                     80: .Pa ssh_known_hosts :
                     81: .Bd -literal
1.4.2.2 ! jason      82: $ ssh-keyscan -f ssh_hosts | sort -u - ssh_known_hosts | \e\
1.1       markus     83:        diff ssh_known_hosts -
                     84: .Ed
                     85: .Pp
                     86: .Sh FILES
                     87: .Pp
                     88: .Pa Input format:
                     89: 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
                     90: .Pp
                     91: .Pa Output format:
                     92: host-or-namelist bits exponent modulus
                     93: .Pp
                     94: .Pa /etc/ssh_known_hosts
                     95: .Sh BUGS
                     96: It generates "Connection closed by remote host" messages on the consoles
                     97: of all the machines it scans.
                     98: This is because it opens a connection to the ssh port, reads the public
                     99: key, and drops the connection as soon as it gets the key.
                    100: .Sh SEE ALSO
1.4.2.2 ! jason     101: .Xr ssh 1 ,
1.1       markus    102: .Xr sshd 8
                    103: .Sh AUTHOR
                    104: David Mazieres <dm@lcs.mit.edu>