我需要从服务器A复制一个文件，该文件只能先连接到服务器B才能访问

Question

I need to copy a file (~9 gigs) from a server, let's call it server B. I can only ssh into server B by first connecting to server A. I am trying to use scp to copy a file to my local machine. I was simply going to use scp to copy the file first to server A, and then again to copy to my local machine - unfortunately though there is only like half a gig of disk space available to me on server A. Is there any way to copy it directly from server B? I cannot use ssh to connect to server B directly from my computer. I'm using terminal on mac.

Answer 1

If your computer and the jump host (server A) are both running OpenSSH v7.3 or later, you can use the ProxyJump option to do this automatically:

scp -oProxyJump=userA@serverA userB@serverB:remoteFile localDest

What this does is open an SSH connection to server A, then tunnel over that to open an SSH (/scp) connection from the local computer to server B, then transfer the file over that connection. Note that it'll ask for two passwords as it connects: first serverA, then serverB.

You can also automate this by creating an ssh config file on your computer (~/.ssh/config), and making an entry something like this:

Host serverB
    ProxyJump userA@serverA

...which tells ssh (and scp) to automatically do the ProxyJump whenever you request a connection to serverB. See the OpenSSH docs on the config file for more details.

If you don't have a new enough OpenSSH on both computers but netcat (or nc or something similar) is available on serverA, you can probably also get the same effect with a ProxyCommand option. See this superuser question .