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ssh-keyscan(1)                   User Commands                  ssh-keyscan(1)



NAME
       ssh-keyscan - gather public ssh host keys of a number of hosts

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  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 connection
                               was  initiated to a host or since the last time
                               anything was read from that host,  the  connec-
                               tion is closed and the host in question is con-
                               sidered 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  messages
                               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:


       tab()    allbox;    cw(2.750000i)|     cw(2.750000i)     lw(2.750000i)|
       lw(2.750000i).    ATTRIBUTE  TYPEATTRIBUTE  VALUE  AvailabilitySUNWsshu
       Interface StabilityEvolving


SEE ALSO
       ssh(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.



SunOS 5.10                        24 Jul 2004                   ssh-keyscan(1)