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 system.

       -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, respectively.

               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,  (excluding  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)

Debian                                            June 17, 2010                                   SSH-COPY-ID(1)