gather ssh public keys
see also :
[-46Hv] [-f file]
[host | addrlist namelist]
add an example, a script, a trick and tips
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-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \
sort -u - ssh_known_hosts | diff ssh_known_hosts -
for i in $@;
ssh-keyscan -t rsa,dsa $i
ssh-keyscan $HOST >
ssh-keygen -l -f $CERTFILE
ssh-keyscan -t ecdsa,dsa,rsa $1
ssh-keygen -l -f $tmp_file
ssh-keyscan -t dsa localhost >> $HOME/.ssh/known_hosts
ssh-keyscan -t dsa `hostname
-f` >> $HOME/.ssh/known_hosts
ssh-keyscan -t dsa `hostname` >>
result=`grep "ssh-rsa" $HOME/.ssh/known_hosts 2>/dev/null | wc
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
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
ssh-keyscan to use IPv4 addresses only.
ssh-keyscan to use IPv6 addresses only.
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
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.
Port to connect to on the
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.
Specifies the type of the key
to fetch from the scanned hosts. The possible values are
’’rsa1’’ for protocol version 1 and
’’rsa’’ for protocol version 2.
Multiple values may be specified by separating them with
commas. The default is to fetch
Causes ssh-keyscan to print debugging messages about
Output format for rsa1 keys:
host-or-namelist bits exponent modulus
Output format for rsa, dsa and ecdsa keys:
host-or-namelist keytype base64-encoded-key
Where keytype is either
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.
It generates "Connection
closed by remote host" messages on 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.
July 18, 2013 BSD
ssh , sshd
<dm[:at:]lcs.mit[:dot:]edu> wrote the initial version, and Wayne
Davison <wayned[:at:]users.sourceforge[:dot:]net> added support
for protocol version 2.