— Gather secure shell
[host | addrlist
is a utility for gathering the public SSH host
keys of a number of hosts. It was designed to aid in building and verifying
files, the format of which is documented in
provides a minimal
interface suitable for use by shell and perl scripts.
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:
- Force ssh-keyscan to use IPv4 addresses
- Force ssh-keyscan to use IPv6 addresses
- Print keys found as DNS Resource Records (CERT or SSHFP).
The default is to print keys in a format usable as a
ssh(1) known_hosts 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:
- 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.
- Connect to port on the remote
- 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.
- Specify the host-key algorithms as pattern-list to fetch
from the scanned hosts. See PATTERNS in
ssh_config(5) for more information on patterns.
The supported host-key algorithms are
“ecdsa-sha2-nistp384”, or “ecdsa-sha2-nistp521”.
The default is “*” , i.e. all supported algorithms.
Note that host-key algorithms “rsa-sha2-256”,
“rsa-sha2-512”, and “ssh-rsa” share one and the
same format of host-key.
- 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
attacks. On the other hand, if the security model allows such a
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.
Print the all RSA host-keys 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-keyscan -f ssh_hosts | \
sort -u - ssh_known_hosts | diff ssh_known_hosts -
Storing Certificates in the Domain Name
System (DNS), RFC 2538,
Resource Records for the DNS Security
Extensions, RFC 4034,
Using DNS to Securely Publish Secure Shell
(SSH) Key Fingerprints, RFC 4255,
the initial version, Wayne Davison
added support for protocol version 2, and Roumen
contributed support for X.509 certificates.