1SSH-KEYSCAN(1) General Commands Manual SSH-KEYSCAN(1) 2 3NAME 4 ssh-keyscan M-bM-^@M-^S gather ssh public keys 5 6SYNOPSIS 7 ssh-keyscan [-46cHv] [-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 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 60SECURITY 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 68FILES 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 86EXAMPLES 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 97SEE ALSO 98 ssh(1), sshd(8) 99 100AUTHORS 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 105BUGS 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 111OpenBSD 6.0 November 8, 2015 OpenBSD 6.0 112