SSH-COPY-ID(1) | General Commands Manual | SSH-COPY-ID(1) |
ssh-copy-id
—
ssh-copy-id |
[-f ] [-n ]
[-i [identity_file]]
[-p port]
[-o ssh_option]
[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, 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
-h
,
-
?-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).
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.
-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 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)).
$Mdocdate: June 17 2010 $ | NetBSD 9.4 |