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NAME | SYNOPSIS | DESCRIPTION | FILES | EXAMPLES | SEE ALSO | AUTHORS | COLOPHON |
SSH-KEYSCAN(1) BSD General Commands Manual SSH-KEYSCAN(1)
ssh-keyscan — gather SSH public keys from servers
ssh-keyscan [-46cDHv] [-f file] [-p port] [-T timeout] [-t type]
[host | addrlist namelist]
ssh-keyscan is a utility for gathering the public SSH host keys of a
number of hosts. It was designed to aid in building and verifying
ssh_known_hosts files, the format of which is documented in sshd(8).
ssh-keyscan provides a minimal interface suitable for use by shell and
perl scripts.
ssh-keyscan uses non-blocking socket I/O to contact as many hosts as
possible in parallel, so it is very efficient. The keys from a domain
of 1,000 hosts can be collected in tens of seconds, even when some of
those hosts are down or do not run sshd(8). For scanning, one does not
need login access to the machines that are being scanned, nor does the
scanning process involve any encryption.
The options are as follows:
-4 Force ssh-keyscan to use IPv4 addresses only.
-6 Force ssh-keyscan to use IPv6 addresses only.
-c Request certificates from target hosts instead of plain keys.
-D Print keys found as SSHFP DNS records. The default is to print
keys in a format usable as a ssh(1) known_hosts file.
-f file
Read hosts or “addrlist namelist” pairs from file, one per
line. If ‘-’ is supplied instead of a filename, ssh-keyscan
will read from the standard input. Input is expected in the
format:
1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
-H Hash all hostnames and addresses in the output. Hashed names
may be used normally by ssh(1) and sshd(8), but they do not
reveal identifying information should the file's contents be
disclosed.
-p port
Connect to port on the remote host.
-T timeout
Set the timeout for connection attempts. If timeout seconds
have elapsed since a connection was initiated to a host or
since the last time anything was read from that host, the con‐
nection is closed and the host in question considered unavail‐
able. The default is 5 seconds.
-t type
Specify the type of the key to fetch from the scanned hosts.
The possible values are “dsa”, “ecdsa”, “ed25519”, or “rsa”.
Multiple values may be specified by separating them with com‐
mas. The default is to fetch “rsa”, “ecdsa”, and “ed25519”
keys.
-v Verbose mode: print debugging messages about progress.
If an ssh_known_hosts file is constructed using ssh-keyscan without
verifying the keys, users will be vulnerable to man in the middle
attacks. On the other hand, if the security model allows such a risk,
ssh-keyscan can help in the detection of tampered keyfiles or man in
the middle attacks which have begun after the ssh_known_hosts file was
created.
/etc/ssh/ssh_known_hosts
Print the RSA host key for machine hostname:
$ ssh-keyscan -t rsa hostname
Find all hosts from the file ssh_hosts which have new or different keys
from those in the sorted file ssh_known_hosts:
$ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \
sort -u - ssh_known_hosts | diff ssh_known_hosts -
ssh(1), sshd(8)
Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints, RFC
4255, 2006.
David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
Davison <wayned@users.sourceforge.net> added support for protocol ver‐
sion 2.
This page is part of the openssh (Portable OpenSSH) project. Informa‐
tion about the project can be found at
http://www.openssh.com/portable.html. If you have a bug report for
this manual page, see ⟨http://www.openssh.com/report.html⟩. This page
was obtained from the tarball openssh-8.3p1.tar.gz fetched from
⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
2020-08-13. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original manual
page), send a mail to man-pages@man7.org
BSD November 30, 2019 BSD