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NAME | SYNOPSIS | DESCRIPTION | FILES | EXAMPLES | SEE ALSO | AUTHORS | COLOPHON |
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SSH-KEYSCAN(1) General Commands Manual SSH-KEYSCAN(1)
ssh-keyscan — gather SSH public keys from servers
ssh-keyscan [-46cDHv] [-f file] [-O option] [-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.
Hosts to be scanned may be specified by hostname, address or by
CIDR network range (e.g. 192.168.16/28). If a network range is
specified, then all addresses in that range will be scanned.
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. Names
read from a file must start with an address, hostname or
CIDR network range to be scanned. Addresses and
hostnames may optionally be followed by comma-separated
name or address aliases that will be copied to the
output. For example:
192.168.11.0/24
10.20.1.1
happy.example.org
10.0.0.1,sad.example.org
-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.
-O option
Specify a key/value option. At present, only a single
option is supported:
hashalg=algorithm
Selects a hash algorithm to use when printing
SSHFP records using the -D flag. Valid
algorithms are “sha1” and “sha256”. The default
is to print both.
-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 connection is closed and the host in question
considered unavailable. 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”, “ecdsa-sk”, “ed25519-sk”, or “rsa”. Multiple
values may be specified by separating them with commas.
The default is to fetch “rsa”, “ecdsa”, “ed25519”,
“ecdsa-sk”, and “ed25519-sk” 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
Search a network range, printing all supported key types:
$ ssh-keyscan 192.168.0.64/25
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 version 2.
This page is part of the openssh (Portable OpenSSH) project.
Information 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-9.7p1.tar.gz
fetched from
⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
2024-06-14. If you discover any rendering problems in this HTML
version 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
GNU February 10, 2023 SSH-KEYSCAN(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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