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_filedefault_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
-n
-s
-t
target_path-p
port, -o
ssh_optionRather 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
ssh-copy-id
script itself. It sets the shell's -x flag, so that you can see the
commands being run.-h
,
-
?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:
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
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)).
June 17, 2010 | macOS 14.6 |