SSH-COPY-ID(1)                BSD General Commands Manual                SSH-COPY-ID(1)

NAME
     ssh-copy-id — use locally available keys to authorise logins on a remote machine

SYNOPSIS
     ssh-copy-id [-f] [-n] [-i [identity_file]] [-p port] [-o ssh_option]
                 [user@]hostname
     ssh-copy-id -h | -?

DESCRIPTION
     ssh-copy-id is a script that uses ssh(1) to log into a remote machine (presumably
     using a login password, so password authentication should be enabled, unless
     you've done some clever use of multiple identities).  It assembles a list of one
     or more fingerprints (as described below) and tries to log in with each key, to
     see if any of them are already installed (of course, if you are not using
     ssh-agent(1) this may result in you being repeatedly prompted for pass-phrases).
     It then assembles a list of those that failed to log in, and using ssh, enables
     logins with those keys on the remote server.  By default it adds the keys by
     appending them to the remote user's ~/.ssh/authorized_keys (creating the file, and
     directory, if necessary).  It is also capable of detecting if the remote system is
     a NetScreen, and using its ‘set ssh pka-dsa key ...’ command instead.

     The options are as follows:

     -i identity_file
             Use only the key(s) contained in identity_file (rather than looking for
             identities via ssh-add(1) or in the default_ID_file).  If the filename
             does not end in .pub this is added.  If the filename is omitted, the
             default_ID_file is used.

             Note that this can be used to ensure that the keys copied have the comment
             one prefers and/or extra options applied, by ensuring that the key file
             has these set as preferred before the copy is attempted.

     -f      Forced mode: doesn't check if the keys are present on the remote server.
             This means that it does not need the private key.  Of course, this can
             result in more than one copy of the key being installed on the remote sys‐
             tem.

     -n      do a dry-run.  Instead of installing keys on the remote system simply
             prints the key(s) that would have been installed.

     -h, -?  Print Usage summary

     -p port, -o ssh_option
             These two options are simply passed through untouched, along with their
             argument, to allow one to set the port or other ssh(1) options, respec‐
             tively.

             Rather than specifying these as command line options, it is often better
             to use (per-host) settings in ssh(1)'s configuration file: ssh_config(5).

     Default behaviour without -i, is to check if ‘ssh-add -L’ provides any output, and
     if so those keys are used.  Note that this results in the comment on the key being
     the filename that was given to ssh-add(1) when the key was loaded into your
     ssh-agent(1) rather than the comment contained in that file, which is a bit of a
     shame.  Otherwise, if ssh-add(1) provides no keys contents of the default_ID_file
     will be used.

     The default_ID_file is the most recent file that matches: ~/.ssh/id*.pub, (exclud‐
     ing those that match ~/.ssh/*-cert.pub) so if you create a key that is not the one
     you want ssh-copy-id to use, just use touch(1) on your preferred key's .pub file
     to reinstate it as the most recent.

EXAMPLES
     If you have already installed keys from one system on a lot of remote hosts, and
     you then create a new key, on a new client machine, say, it can be difficult to
     keep track of which systems on which you've installed the new key.  One way of
     dealing with this is to load both the new key and old key(s) into your
     ssh-agent(1).  Load the new key first, without the -c option, then load one or
     more old keys into the agent, possibly by ssh-ing to the client machine that has
     that old key, using the -A option to allow agent forwarding:

           user@newclient$ ssh-add
           user@newclient$ ssh -A old.client
           user@oldl$ ssh-add -c
           ... prompt for pass-phrase ...
           user@old$ logoff
           user@newclient$ ssh someserver

     now, if the new key is installed on the server, you'll be allowed in unprompted,
     whereas if you only have the old key(s) enabled, you'll be asked for confirmation,
     which is your cue to log back out and run

           user@newclient$ ssh-copy-id -i someserver

     The reason you might want to specify the -i option in this case is to ensure that
     the comment on the installed key is the one from the .pub file, rather than just
     the filename that was loaded into you agent.  It also ensures that only the id you
     intended is installed, rather than all the keys that you have in your
     ssh-agent(1).  Of course, you can specify another id, or use the contents of the
     ssh-agent(1) as you prefer.

     Having mentioned ssh-add(1)'s -c option, you might consider using this whenever
     using agent forwarding to avoid your key being hijacked, but it is much better to
     instead use ssh(1)'s ProxyCommand and -W option, to bounce through remote servers
     while always doing direct end-to-end authentication. This way the middle hop(s)
     don't get access to your ssh-agent(1).  A web search for ‘ssh proxycommand nc’
     should prove enlightening (N.B. the modern approach is to use the -W option,
     rather than nc(1)).

SEE ALSO
     ssh(1), ssh-agent(1), sshd(8)

BSD                                  June 17, 2010                                  BSD

Usage: /usr/bin/ssh-copy-id [-h|-?|-f|-n] [-i [identity_file]] [-p port] [[-o <ssh -o options>] ...] [user@]hostname
        -f: force mode -- copy keys without trying to check if they are already installed
        -n: dry run    -- no keys are actually copied
        -h|-?: print this help