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aa144206 | 1 | .\" $OpenBSD: ssh-keyscan.1,v 1.6 2001/06/05 05:05:39 pvalchev Exp $ |
4371658c | 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 | |
aa144206 | 7 | .\" OpenBSD project by leaving this copyright notice intact. |
23c2a7a5 | 8 | .\" |
f6fdbddf | 9 | .Dd January 1, 1996 |
4371658c | 10 | .Dt SSH-KEYSCAN 1 |
f6fdbddf | 11 | .Os |
12 | .Sh NAME | |
13 | .Nm ssh-keyscan | |
14 | .Nd gather ssh public keys | |
15 | .Sh SYNOPSIS | |
16 | .Nm ssh-keyscan | |
17 | .Op Fl t Ar timeout | |
18 | .Op Ar -- | host | addrlist namelist | |
19 | .Op Fl f Ar files ... | |
20 | .Sh DESCRIPTION | |
21 | .Nm | |
22 | is a utility for gathering the public ssh host keys of a number of | |
23 | hosts. It was designed to aid in building and verifying | |
24 | .Pa ssh_known_hosts | |
25 | files. | |
26 | .Nm | |
27 | provides a minimal interface suitable for use by shell and perl | |
28 | scripts. | |
29 | .Pp | |
30 | .Nm | |
31 | uses non-blocking socket I/O to contact as many hosts as possible in | |
32 | parallel, so it is very efficient. The keys from a domain of 1,000 | |
33 | hosts can be collected in tens of seconds, even when some of those | |
34 | hosts are down or do not run ssh. You do not need login access to the | |
05cc0c99 | 35 | machines you are scanning, nor does the scanning process involve |
f6fdbddf | 36 | any encryption. |
37 | .Sh SECURITY | |
38 | If you make an ssh_known_hosts file using | |
39 | .Nm | |
40 | without verifying the keys, you will be vulnerable to | |
41 | .I man in the middle | |
42 | attacks. | |
43 | On the other hand, if your security model allows such a risk, | |
44 | .Nm | |
45 | can help you detect tampered keyfiles or man in the middle attacks which | |
46 | have begun after you created your ssh_known_hosts file. | |
47 | .Sh OPTIONS | |
48 | .Bl -tag -width Ds | |
49 | .It Fl t | |
50 | Set the timeout for connection attempts. If | |
51 | .Pa timeout | |
52 | seconds have elapsed since a connection was initiated to a host or since the | |
53 | last time anything was read from that host, then the connection is | |
54 | closed and the host in question considered unavailable. Default is 5 | |
55 | seconds. | |
56 | .It Fl f | |
57 | Read hosts or | |
58 | .Pa addrlist namelist | |
59 | pairs from this file, one per line. | |
60 | If | |
61 | .Pa - | |
62 | is supplied instead of a filename, | |
63 | .Nm | |
64 | will read hosts or | |
65 | .Pa addrlist namelist | |
66 | pairs from the standard input. | |
9616313f | 67 | .El |
f6fdbddf | 68 | .Sh EXAMPLES |
69 | .Pp | |
70 | Print the host key for machine | |
71 | .Pa hostname : | |
72 | .Bd -literal | |
73 | ssh-keyscan hostname | |
74 | .Ed | |
75 | .Pp | |
76 | Find all hosts from the file | |
77 | .Pa ssh_hosts | |
78 | which have new or different keys from those in the sorted file | |
79 | .Pa ssh_known_hosts : | |
80 | .Bd -literal | |
4371658c | 81 | $ ssh-keyscan -f ssh_hosts | sort -u - ssh_known_hosts | \e\ |
f6fdbddf | 82 | diff ssh_known_hosts - |
83 | .Ed | |
84 | .Pp | |
85 | .Sh FILES | |
86 | .Pp | |
87 | .Pa Input format: | |
88 | 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4 | |
89 | .Pp | |
90 | .Pa Output format: | |
91 | host-or-namelist bits exponent modulus | |
92 | .Pp | |
93 | .Pa /etc/ssh_known_hosts | |
94 | .Sh BUGS | |
95 | It generates "Connection closed by remote host" messages on the consoles | |
96 | of all the machines it scans. | |
97 | This is because it opens a connection to the ssh port, reads the public | |
98 | key, and drops the connection as soon as it gets the key. | |
99 | .Sh SEE ALSO | |
4371658c | 100 | .Xr ssh 1 , |
f6fdbddf | 101 | .Xr sshd 8 |
102 | .Sh AUTHOR | |
103 | David Mazieres <dm@lcs.mit.edu> |