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authorColin Watson <cjwatson@debian.org>2010-01-01 17:10:56 +0000
committerColin Watson <cjwatson@debian.org>2010-01-01 17:10:56 +0000
commit54af7a4ae8d455791a631bdfaade4b64436ae16a (patch)
treee0ae21993bfc33f09c820b8b2e6b408ad855f4ff /ssh-keyscan.0
parentfaec50b554730338c0e9f34966c11368920b6a78 (diff)
parentef94e5613d37bcbf880f21ee6094e4b1c7683a4c (diff)
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1SSH-KEYSCAN(1) OpenBSD Reference Manual SSH-KEYSCAN(1)
2
3NAME
4 ssh-keyscan - gather ssh public keys
5
6SYNOPSIS
7 ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type]
8 [host | addrlist namelist] ...
9
10DESCRIPTION
11 ssh-keyscan is a utility for gathering the public ssh host keys of a num-
12 ber 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 pos-
17 sible 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 pro-
21 cess 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 -f file
30 Read hosts or addrlist namelist pairs from this file, one per
31 line. If - is supplied instead of a filename, ssh-keyscan will
32 read hosts or addrlist namelist pairs from the standard input.
33
34 -H Hash all hostnames and addresses in the output. Hashed names may
35 be used normally by ssh and sshd, but they do not reveal identi-
36 fying information should the file's contents be disclosed.
37
38 -p port
39 Port to connect to on the remote host.
40
41 -T timeout
42 Set the timeout for connection attempts. If timeout seconds have
43 elapsed since a connection was initiated to a host or since the
44 last time anything was read from that host, then the connection
45 is closed and the host in question considered unavailable. De-
46 fault is 5 seconds.
47
48 -t type
49 Specifies the type of the key to fetch from the scanned hosts.
50 The possible values are ``rsa1'' for protocol version 1 and
51 ``rsa'' or ``dsa'' for protocol version 2. Multiple values may
52 be specified by separating them with commas. The default is
53 ``rsa''.
54
55 -v Verbose mode. Causes ssh-keyscan to print debugging messages
56 about its progress.
57
58SECURITY
59 If an ssh_known_hosts file is constructed using ssh-keyscan without veri-
60 fying the keys, users will be vulnerable to man in the middle attacks.
61 On the other hand, if the security model allows such a risk, ssh-keyscan
62 can help in the detection of tampered keyfiles or man in the middle at-
63 tacks which have begun after the ssh_known_hosts file was created.
64
65FILES
66 Input format:
67
68 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
69
70 Output format for rsa1 keys:
71
72 host-or-namelist bits exponent modulus
73
74 Output format for rsa and dsa keys:
75
76 host-or-namelist keytype base64-encoded-key
77
78 Where keytype is either ``ssh-rsa'' or ``ssh-dss''.
79
80 /etc/ssh/ssh_known_hosts
81
82EXAMPLES
83 Print the rsa host key for machine hostname:
84
85 $ ssh-keyscan hostname
86
87 Find all hosts from the file ssh_hosts which have new or different keys
88 from those in the sorted file ssh_known_hosts:
89
90 $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \
91 sort -u - ssh_known_hosts | diff ssh_known_hosts -
92
93SEE ALSO
94 ssh(1), sshd(8)
95
96AUTHORS
97 David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
98 Davison <wayned@users.sourceforge.net> added support for protocol version
99 2.
100
101BUGS
102 It generates "Connection closed by remote host" messages on the consoles
103 of all the machines it scans if the server is older than version 2.9.
104 This is because it opens a connection to the ssh port, reads the public
105 key, and drops the connection as soon as it gets the key.
106
107OpenBSD 4.5 December 29, 2008 2