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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@lcs.mit.edu> wrote the initial version, and Wayne | ||
102 | Davison <wayned@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 5.9 November 8, 2015 OpenBSD 5.9 | ||