# ssh-copy-id

## NAME



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


## SYNOPSIS



           **ssh-copy-id**[**-f**] [**-n**] [**-s**] [**-x**] [**-i**[_identity_file_]] [**-t**
           _target_path_] [**-F** _ssh_config_] [[**-o** _ssh_option_] ...] [**-p** _port_]
           [_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_(1), 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.
    
           **-s** SFTP mode: usually the public keys are installed by
                   executing commands on the remote side.  With this option
                   the user's _~/.ssh/authorized_keys_ file will be downloaded,
                   modified locally and uploaded with sftp.  This option is
                   useful if the server has restrictions on commands which
                   can be used on the remote side.
    
           **-t** _target_path_
                   the path on the target system where the keys should be
                   added (defaults to ".ssh/authorized_keys")
    
           **-p** _port_
                   Specifies the port to connect to on the remote host.
    
           **-F** _ssh_config_ , **-o** _ssh_option_
                   These options are simply passed through untouched (with
                   their argument) to ssh/sftp, allowing one to set an
                   alternative config file, or other 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).
    
           **-x** This option is for debugging the **ssh-copy-id** script
                   itself.  It sets the shell's -x flag, so that you can see
                   the commands being run.
    
           **-h** , **-**?  Print Usage summary
    
           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
           your 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 (NB the modern
           approach is to use the **-W** option, rather than _nc_(1)).
    


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