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Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.4.2.1

1.4       deraadt     1: .\"    $OpenBSD: ssh-keyscan.1,v 1.3 2001/01/29 01:58:18 niklas Exp $
                      2: .\"
1.1       markus      3: .Dd January 1, 1996
1.4.2.1 ! jason       4: .Dt ssh-keyscan 1
1.1       markus      5: .Os
                      6: .Sh NAME
                      7: .Nm ssh-keyscan
                      8: .Nd gather ssh public keys
                      9: .Sh SYNOPSIS
                     10: .Nm ssh-keyscan
                     11: .Op Fl t Ar timeout
                     12: .Op Ar -- | host | addrlist namelist
                     13: .Op Fl f Ar files ...
                     14: .Sh DESCRIPTION
                     15: .Nm
                     16: is a utility for gathering the public ssh host keys of a number of
                     17: hosts.  It was designed to aid in building and verifying
                     18: .Pa ssh_known_hosts
                     19: files.
                     20: .Nm
                     21: provides a minimal interface suitable for use by shell and perl
                     22: scripts.
                     23: .Pp
                     24: .Nm
                     25: uses non-blocking socket I/O to contact as many hosts as possible in
                     26: parallel, so it is very efficient.  The keys from a domain of 1,000
                     27: hosts can be collected in tens of seconds, even when some of those
                     28: hosts are down or do not run ssh.  You do not need login access to the
                     29: machines you are scanning, nor does does the scanning process involve
                     30: any encryption.
                     31: .Sh SECURITY
                     32: If you make an ssh_known_hosts file using
                     33: .Nm
                     34: without verifying the keys, you will be vulnerable to
                     35: .I man in the middle
                     36: attacks.
                     37: On the other hand, if your security model allows such a risk,
                     38: .Nm
                     39: can help you detect tampered keyfiles or man in the middle attacks which
                     40: have begun after you created your ssh_known_hosts file.
                     41: .Sh OPTIONS
                     42: .Bl -tag -width Ds
                     43: .It Fl t
                     44: Set the timeout for connection attempts.  If
                     45: .Pa timeout
                     46: seconds have elapsed since a connection was initiated to a host or since the
                     47: last time anything was read from that host, then the connection is
                     48: closed and the host in question considered unavailable.  Default is 5
                     49: seconds.
                     50: .It Fl f
                     51: Read hosts or
                     52: .Pa addrlist namelist
                     53: pairs from this file, one per line.
                     54: If
                     55: .Pa -
                     56: is supplied instead of a filename,
                     57: .Nm
                     58: will read hosts or
                     59: .Pa addrlist namelist
                     60: pairs from the standard input.
1.2       itojun     61: .El
1.1       markus     62: .Sh EXAMPLES
                     63: .Pp
                     64: Print the host key for machine
                     65: .Pa hostname :
                     66: .Bd -literal
                     67: ssh-keyscan hostname
                     68: .Ed
                     69: .Pp
                     70: Find all hosts from the file
                     71: .Pa ssh_hosts
                     72: which have new or different keys from those in the sorted file
                     73: .Pa ssh_known_hosts :
                     74: .Bd -literal
1.4.2.1 ! jason      75: ssh-keyscan -f ssh_hosts | sort -u - ssh_known_hosts | \e\
1.1       markus     76:        diff ssh_known_hosts -
                     77: .Ed
                     78: .Pp
                     79: .Sh FILES
                     80: .Pp
                     81: .Pa Input format:
                     82: 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
                     83: .Pp
                     84: .Pa Output format:
                     85: host-or-namelist bits exponent modulus
                     86: .Pp
                     87: .Pa /etc/ssh_known_hosts
                     88: .Sh BUGS
                     89: It generates "Connection closed by remote host" messages on the consoles
                     90: of all the machines it scans.
                     91: This is because it opens a connection to the ssh port, reads the public
                     92: key, and drops the connection as soon as it gets the key.
                     93: .Sh SEE ALSO
1.4.2.1 ! jason      94: .Xr ssh 1
1.1       markus     95: .Xr sshd 8
                     96: .Sh AUTHOR
                     97: David Mazieres <dm@lcs.mit.edu>