ssh-keyscan(1) - phpMan

SSH-KEYSCAN(1) BSD General Commands Manual SSH-KEYSCAN(1)

NAME
ssh-keyscan -- gather ssh public keys

SYNOPSIS
ssh-keyscan [-46cHv] [-f file] [-p port] [-T timeout] [-t type] [host | addrlist namelist]
...

DESCRIPTION
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. 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 ssh. 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 Forces ssh-keyscan to use IPv4 addresses only.

-6 Forces ssh-keyscan to use IPv6 addresses only.

-c Request certificates from target hosts instead of plain keys.

-f file
Read hosts or ``addrlist namelist'' pairs from file, one per line. If - is supplied
instead of a filename, ssh-keyscan will read hosts or ``addrlist namelist'' pairs
from the standard input.

-H Hash all hostnames and addresses in the output. Hashed names may be used normally
by ssh and sshd, but they do not reveal identifying information should the file's
contents be disclosed.

-p port
Port to connect to 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, then the connection is closed and the host in question considered
unavailable. Default is 5 seconds.

-t type
Specifies the type of the key to fetch from the scanned hosts. The possible values
are ``rsa1'' for protocol version 1 and ``dsa'', ``ecdsa'', ``ed25519'', or ``rsa''
for protocol version 2. Multiple values may be specified by separating them with
commas. The default is to fetch ``rsa'', ``ecdsa'', and ``ed25519'' keys.

-v Verbose mode. Causes ssh-keyscan to print debugging messages about its progress.

SECURITY
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.

FILES
Input 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

Output format for RSA1 keys:

host-or-namelist bits exponent modulus

Output format for RSA, DSA, ECDSA, and Ed25519 keys:

host-or-namelist keytype base64-encoded-key

Where keytype is either ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'',
``ecdsa-sha2-nistp521'', ``ssh-ed25519'', ``ssh-dss'' or ``ssh-rsa''.

/etc/ssh/ssh_known_hosts

EXAMPLES
Print the rsa host key for machine hostname:

$ ssh-keyscan 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 -