1.ig \" -*- nroff -*- 2Copyright (c) 1999-2020 hands.com Ltd. <http://hands.com/> 3 4Redistribution and use in source and binary forms, with or without 5modification, are permitted provided that the following conditions 6are met: 71. Redistributions of source code must retain the above copyright 8 notice, this list of conditions and the following disclaimer. 92. Redistributions in binary form must reproduce the above copyright 10 notice, this list of conditions and the following disclaimer in the 11 documentation and/or other materials provided with the distribution. 12 13THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23.. 24.Dd $Mdocdate: June 17 2010 $ 25.Dt SSH-COPY-ID 1 26.Os 27.Sh NAME 28.Nm ssh-copy-id 29.Nd use locally available keys to authorise logins on a remote machine 30.Sh SYNOPSIS 31.Nm 32.Op Fl f 33.Op Fl n 34.Op Fl s 35.Op Fl i Op Ar identity_file 36.Op Fl p Ar port 37.Op Fl o Ar ssh_option 38.Op Ar user Ns @ Ns 39.Ar hostname 40.Nm 41.Fl h | Fl ? 42.br 43.Sh DESCRIPTION 44.Nm 45is a script that uses 46.Xr ssh 1 47to log into a remote machine (presumably using a login password, 48so password authentication should be enabled, unless you've done some 49clever use of multiple identities). It assembles a list of one or more 50fingerprints (as described below) and tries to log in with each key, to 51see if any of them are already installed (of course, if you are not using 52.Xr ssh-agent 1 53this may result in you being repeatedly prompted for pass-phrases). 54It then assembles a list of those that failed to log in, and using ssh, 55enables logins with those keys on the remote server. By default it adds 56the keys by appending them to the remote user's 57.Pa ~/.ssh/authorized_keys 58(creating the file, and directory, if necessary). It is also capable 59of detecting if the remote system is a NetScreen, and using its 60.Ql set ssh pka-dsa key ... 61command instead. 62.Pp 63The options are as follows: 64.Bl -tag -width Ds 65.It Fl i Ar identity_file 66Use only the key(s) contained in 67.Ar identity_file 68(rather than looking for identities via 69.Xr ssh-add 1 70or in the 71.Ic default_ID_file ) . 72If the filename does not end in 73.Pa .pub 74this is added. If the filename is omitted, the 75.Ic default_ID_file 76is used. 77.Pp 78Note that this can be used to ensure that the keys copied have the 79comment one prefers and/or extra options applied, by ensuring that the 80key file has these set as preferred before the copy is attempted. 81.It Fl f 82Forced mode: doesn't check if the keys are present on the remote server. 83This means that it does not need the private key. Of course, this can result 84in more than one copy of the key being installed on the remote system. 85.It Fl n 86do a dry-run. Instead of installing keys on the remote system simply 87prints the key(s) that would have been installed. 88.It Fl s 89SFTP mode: usually the public keys are installed by executing commands on the remote side. 90With this option the user's 91.Pa ~/.ssh/authorized_keys 92file will be downloaded, modified locally and uploaded with sftp. 93This option is useful if the server has restrictions on commands which can be used on the remote side. 94.It Fl h , Fl ? 95Print Usage summary 96.It Fl p Ar port , Fl o Ar ssh_option 97These two options are simply passed through untouched, along with their 98argument, to allow one to set the port or other 99.Xr ssh 1 100options, respectively. 101.Pp 102Rather than specifying these as command line options, it is often better to use (per-host) settings in 103.Xr ssh 1 Ns 's 104configuration file: 105.Xr ssh_config 5 . 106.El 107.Pp 108Default behaviour without 109.Fl i , 110is to check if 111.Ql ssh-add -L 112provides any output, and if so those keys are used. Note that this results in 113the comment on the key being the filename that was given to 114.Xr ssh-add 1 115when the key was loaded into your 116.Xr ssh-agent 1 117rather than the comment contained in that file, which is a bit of a shame. 118Otherwise, if 119.Xr ssh-add 1 120provides no keys contents of the 121.Ic default_ID_file 122will be used. 123.Pp 124The 125.Ic default_ID_file 126is the most recent file that matches: 127.Pa ~/.ssh/id*.pub , 128(excluding those that match 129.Pa ~/.ssh/*-cert.pub ) 130so if you create a key that is not the one you want 131.Nm 132to use, just use 133.Xr touch 1 134on your preferred key's 135.Pa .pub 136file to reinstate it as the most recent. 137.Pp 138.Sh EXAMPLES 139If you have already installed keys from one system on a lot of remote 140hosts, and you then create a new key, on a new client machine, say, 141it can be difficult to keep track of which systems on which you've 142installed the new key. One way of dealing with this is to load both 143the new key and old key(s) into your 144.Xr ssh-agent 1 . 145Load the new key first, without the 146.Fl c 147option, then load one or more old keys into the agent, possibly by 148ssh-ing to the client machine that has that old key, using the 149.Fl A 150option to allow agent forwarding: 151.Pp 152.D1 user@newclient$ ssh-add 153.D1 user@newclient$ ssh -A old.client 154.D1 user@oldl$ ssh-add -c 155.D1 No ... prompt for pass-phrase ... 156.D1 user@old$ logoff 157.D1 user@newclient$ ssh someserver 158.Pp 159now, if the new key is installed on the server, you'll be allowed in 160unprompted, whereas if you only have the old key(s) enabled, you'll be 161asked for confirmation, which is your cue to log back out and run 162.Pp 163.D1 user@newclient$ ssh-copy-id -i someserver 164.Pp 165The reason you might want to specify the -i option in this case is to 166ensure that the comment on the installed key is the one from the 167.Pa .pub 168file, rather than just the filename that was loaded into your agent. 169It also ensures that only the id you intended is installed, rather than 170all the keys that you have in your 171.Xr ssh-agent 1 . 172Of course, you can specify another id, or use the contents of the 173.Xr ssh-agent 1 174as you prefer. 175.Pp 176Having mentioned 177.Xr ssh-add 1 Ns 's 178.Fl c 179option, you might consider using this whenever using agent forwarding 180to avoid your key being hijacked, but it is much better to instead use 181.Xr ssh 1 Ns 's 182.Ar ProxyCommand 183and 184.Fl W 185option, 186to bounce through remote servers while always doing direct end-to-end 187authentication. This way the middle hop(s) don't get access to your 188.Xr ssh-agent 1 . 189A web search for 190.Ql ssh proxycommand nc 191should prove enlightening (N.B. the modern approach is to use the 192.Fl W 193option, rather than 194.Xr nc 1 ) . 195.Sh "SEE ALSO" 196.Xr ssh 1 , 197.Xr ssh-agent 1 , 198.Xr sshd 8 199