I can't sftp directly into a particular host. To move a file from my home machine to the host, I must sftp a file to an intermediate host; ssh into the intermediate host; and sftp the file to the final destination. Is it possible to avoid such madness?
5 Answers
From your local machine you can create am SSH tunnel through the intermediate host to the final host:
ssh user@intermediate -L 2000:final:22 -N
This will open port 2000 on your localhost that will connect directly to the final server on port 22, by tunneling through the intermediate host. Now in another prompt connect with sftp on port 2000 to be tunneled through to the final server, noting that the user specified here is for the final host:
sftp -P 2000 user@localhost
Seems like this belongs on superuser.com or serverfault.com though.
-
Thanks, I'll try that; and you're right it is the wrong forum; sorry.– AnonymousMar 26, 2011 at 22:58
-
After giving the user@localhost password I received the message: Received message too long 1131376238 Mar 29, 2011 at 23:14
-
Many versions of sftp use
-P
for the "sftp_server_path
", rather than the port. Butsftp -o Port=2000
should work. Although if yoursftp
is new enough, it's easier just to use-J
for a ProxyJump as per the other answer. Dec 15, 2022 at 11:24
Since I originally wrote this answer, OpenSSH has added an easier way to do this. If you have at least OpenSSH 8.0 on your home machine and 7.3 on the intermediate host, you can use the new jump host (-J
) option:
sftp -J user@intermediatehost user@finalhost
If you have at least 7.3 on both the home and intermediate hosts, you can do the same thing with the ProxyJump
option in your ~/.ssh/config file:
Host finalhost
ProxyJump user@intermediatehost
With that entry, you can use sftp, scp, and ssh to finalhost, and it'll automatically invoke the tunnel. The only nontransparent part is that it'll prompt for two passwords (intermediatehost followed by finalhost), but if you want you can eliminate that as well with SSH keypairs.
If you don't have new enough versions of OpenSSH, you can still use the ProxyCommand
option to do essentially the same thing:
sftp -o "ProxyCommand=ssh -e none user@intermediatehost exec /usr/bin/nc %h %p 2>/dev/null" user@finalhost
(That's assuming the intermediate host has netcat installed as /usr/bin/nc
-- if not, you may have to find/install some equivalent way of gatewaying stdin&stdout into a TCP session.)
And the equivalent ~/.ssh/config option:
Host finalhost
ProxyCommand ssh -e none user@intermediatehost exec nc %h %p 2>/dev/null
See the OpenSSH Cookbook on Wikibooks for more info.
-
Thanks Gordon. It takes both passwords then halts with the message: Received message too long 1131376238 Mar 29, 2011 at 23:08
-
It sounds like something in the connection -- maybe a login script at one of the hosts, maybe nc -- is writing some extra text over the connection that's confusing sftp (see this FAQ at snailbook.com). 1131376238 is the decimal encoding of the ascii characters "Conn", so it's probably a message like "Connecting to..." "Connected from..." or maybe "Connection failed". Try it with ssh instead of sftp, see if the message is printed visibly and maybe you can tell where it's coming from. Mar 29, 2011 at 23:42
-
ssh worked fine. I should also mention that I am often faced with this question:The authenticity of host 'xxxxx (<no hostip for proxy command>)' can't be established. RSA key fingerprint is 37:40:d4:c7:etc.. Are you sure you want to continue connecting (yes/no)? yes Apr 1, 2011 at 23:49
-
Gordon, very useful! I'm adding this to my text file of command line fu oneliners. Thanks a ton! May 15, 2012 at 19:48
-
You can pipe data to the ssh process running on your machine, then run a command on the intermediate machine which reads stdin and sends it to sftp as appropriate.
This can be done in a oneliner on your local machine, though the quoting of arguments to ssh will require care. I am on my phone right now so unfortunately cannot type the details. Perhaps somebody else can complete this answer as an exercise!
I'm assuming the final host is firewalled and I can only guess at methods you could use to go around it.
For example - expose ssh from your local machine, then ssh to the first host, then ssh to the second and sftp from the final host to your machine.
lets say A and B are the first and second hosts. And the file to be copied is foo
Instead of sftp, you can use the following
cat foo | ssh A "cat - > foo"
Now, you can daisy-chain 2 of these together
cat foo| ssh A "cat - | ssh B \"cat - > foo\" "
-
I like it, so I tried it. It took the password for A, then produced the message: Host key verification failed. Mar 29, 2011 at 23:06