ssh-keyscan [-t timeout] [-- | host | addrlist namelist] [-f files ...]
DESCRIPTION
ssh-keyscan is a utility for gathering the public ssh host keys of a num
ber 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 pos
sible 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. You do not need login access to the
machines you are scanning, nor does the scanning process involve any en
cryption.
SECURITY
If you make an ssh_known_hosts file using ssh-keyscan without verifying
the keys, you will be vulnerable to attacks. On the other hand, if your
security model allows such a risk, ssh-keyscan can help you detect tam
pered keyfiles or man in the middle attacks which have begun after you
created your ssh_known_hosts file.
OPTIONS
-t 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. De
fault is 5 seconds.
-f 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.
EXAMPLES
Print the 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 -f ssh_hosts | sort -u - ssh_known_hosts | \
diff ssh_known_hosts -
FILES
Input format: 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.do
main,n,1.2.3.4,1.2.4.4
Output format: host-or-namelist bits exponent modulus
/etc/ssh/ssh_known_hosts
BUGS
It generates "Connection closed by remote host" messages on the consoles
of all the machines it scans. This is because it opens a connection to
the ssh port, reads the public key, and drops the connection as soon as
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