SSH-KEYSCAN(1)SSH-KEYSCAN(1)NAMEssh-keyscan - gather public ssh host keys of a number of hosts
SYNOPSISssh-keyscan [-v46] [-p port] [-T timeout] [-t type]
[-f file] [-] [host... | addrlist namelist] [...]
DESCRIPTIONssh-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 suit‐
able for use by shell and perl scripts. The output of ssh-keyscan is
directed to standard output.
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 scan‐
ning process involve any encryption.
File Format
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, where keytype is either ssh-rsa or
`ssh-dsa:
host-or-namelist keytype base64-encoded-key
OPTIONS
The following options are supported:
-f filename
Read hosts or addrlist namelist pairs from
this file, one per line. If you specity -
instead of a filename, ssh-keyscan reads
hosts or addrlist namelist pairs from the
standard input.
-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 con‐
nection 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 is considered unavailable. The
default is for timeout is 5 seconds.
-t type
Specify the type of the key to fetch from
the scanned hosts. The possible values for
type are rsa1 for protocol version 1 and
rsa or dsa for protocol version 2. Specify
multiple values by separating them with
commas. The default is rsa1.
-v
Specify verbose mode. Print debugging mes‐
sages about progress.
-4
Force to use IPv4 addresses only.
-6
Forces to use IPv6 addresses only.
SECURITY
If a ssh_known_hosts file is constructed using ssh-keyscan without ver‐
ifying the keys, users are vulnerable to man-in-the-middle attacks. 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.
EXAMPLES
Example 1 Printing the rsa1 Host Key
The following example prints the rsa1 host key for machine hostname:
$ ssh-keyscan hostname
Example 2 Finding All Hosts
The following commands finds 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 -
FILES
/etc/ssh_known_hosts
EXIT STATUS
The following exit values are returned:
0
No usage errors. ssh-keyscan might or might not have succeeded or
failed to scan one, more or all of the given hosts.
1
Usage error.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Evolving │
└────────────────────┴─────────────────┘
SEE ALSOssh(1), sshd(1M), attributes(5)AUTHORS
David Mazieres wrote the initial version, and Wayne Davison added supp‐
port for protocol version 2.
BUGS
ssh—keyscan generates
Connection closed by remote host
messages on the consoles of all machines it scans if the server is
older than version 2.9. This is because ssh-keyscan opens a connection
to the ssh port, reads the public key, and drops the connection as soon
as it gets the key.
Jul 24, 2004 SSH-KEYSCAN(1)
