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NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | COLOPHON |
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SSH-COPY-ID(1) General Commands Manual SSH-COPY-ID(1)
ssh-copy-id — use locally available keys to authorise logins on a
remote machine
ssh-copy-id [-f] [-n] [-s] [-x] [-i [identity_file]] [-p port]
[-o ssh_option] [-t target_path] [user@]hostname ssh-copy-id -h |
-?
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, -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).
-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.
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)).
ssh(1), ssh-agent(1), sshd(8)
This page is part of the openssh (Portable OpenSSH) project.
Information about the project can be found at
http://www.openssh.com/portable.html. If you have a bug report
for this manual page, see ⟨http://www.openssh.com/report.html⟩.
This page was obtained from the tarball openssh-9.7p1.tar.gz
fetched from
⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
2024-06-14. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
GNU June 17, 2010 SSH-COPY-ID(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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