SSH-KEYSCAN(1) UNIX System V (January 1, 1996) SSH-KEYSCAN(1)
NAME
ssh-keyscan - gather ssh public keys
SYNOPSIS
ssh-keyscan [-v46] [-p port] [-T timeout] [-t type] [-f
file] [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:
-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 ``rsa'' or ``dsa'' for protocol version
2. Multiple values may be specified by separating them
with commas. The default is ``rsa1''.
-f filename
Read hosts or addrlist namelist pairs from this file,
one per line. If - is supplied instead of a filename,
ssh-keyscan will read hosts or addrlist namelist pairs
from the standard input.
-v Verbose mode. Causes ssh-keyscan to print debugging
messages about its progress.
-4 Forces ssh-keyscan to use IPv4 addresses only.
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SSH-KEYSCAN(1) UNIX System V (January 1, 1996) SSH-KEYSCAN(1)-6 Forces ssh-keyscan to use IPv6 addresses only.
SECURITY
If a ssh_known_hosts file is constructed using ssh-keyscan
without verifying the keys, users will be vulnerable to
maninthemiddle 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 and dsa keys:
host-or-namelist keytype base64-encoded-key
Where keytype is either ``ssh-rsa'' or ``ssh-dss''.
/etc/openssh/ssh_known_hosts
EXAMPLES
Print the rsa1 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 -f ssh_hosts | \
sort -u - ssh_known_hosts | diff ssh_known_hosts -
SEE ALSO
ssh(1), sshd(8)
AUTHORS
David Mazieres <dm@lcs.mit.edu> wrote the initial version,
and
Wayne Davison <wayned@users.sourceforge.net> added support
for protocol version 2.
BUGS
It generates "Connection closed by remote host" messages on
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SSH-KEYSCAN(1) UNIX System V (January 1, 1996) SSH-KEYSCAN(1)
the consoles of all the machines it scans if the server is
older than version 2.9. This is because it opens a
connection to the ssh port, reads the public key, and drops
the connection as soon as it gets the key.
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