Which is the best way to bring a file from a remot

问题:

When connecting to remote hosts via ssh, I frequently want to bring a file on that system to the local system for viewing or processing. Is there a way to copy the file over without (a) opening a new terminal/pausing the ssh session (b) authenticating again to either the local or remote hosts which works (c) even when one or both of the hosts is behind a NAT router?

The goal is to take advantage of as much of the current state as possible: that there is a connection between the two machines, that I'm authenticated on both, that I'm in the working directory of the file---so I don't have to open another terminal and copy and paste the remote host and path in, which is what I do now. The best solution also wouldn't require any setup before the session began, but if the setup was a one-time or able to be automated, than that's perfectly acceptable.

回答1:

zssh (a ZMODEM wrapper over openssh) does exactly what you want.

• Install zssh and use it instead of openssh (which I assume that you normally use)

• You'll have to have the lrzsz package installed on both systems.

Then, to transfer a file zyxel.png from remote to local host:

antti@local:~$ zssh remote
Press ^@ (C-Space) to enter file transfer mode, then ? for help
...
antti@remote:~$ sz zyxel.png
**B00000000000000
^@
zssh > rz
Receiving: zyxel.png
Bytes received:  104036/ 104036   BPS:16059729

Transfer complete
antti@remote:~$ 

Uploading goes similarly, except that you just switch rz(1) and sz(1).

Putty users can try Le Putty, which has similar functionality.

回答2:

On a linux box I use the ssh-agent and sshfs. You need to setup the sshd to accept connections with key pairs. Then you use ssh-add to add you key to the ssh-agent so you don't have type your password everytime. Be sure to use -t seconds, so the key doesn't stay loaded forever.
ssh-add -t 3600 /home/user/.ssh/ssh_dsa

After that,
sshfs hostname:/ /PathToMountTo/
will mount the server file system on your machine so you have access to it.

Personally, I wrote a small bash script that add my key and mount the servers I use the most, so when I start to work I just have to launch the script and type my passphrase.

回答3:

Using some little known and rarely used features of the openssh implementation you can accomplish precisely what you want!

• takes advantage of the current state
• can use the working directory where you are
• does not require any tunneling setup before the session begins
• does not require opening a separate terminal or connection
• can be used as a one-time deal in an interactive session or can be used as part of an automated session

You should only type what is at each of the local>, remote>, and ssh> prompts in the examples below.

local> ssh username@remote
remote> ~C
ssh> -L6666:localhost:6666
remote> nc -l 6666 < /etc/passwd
remote> ~^Z
[suspend ssh]
[1]+  Stopped                 ssh username@remote
local> (sleep 1; nc localhost 6666 > /tmp/file) & fg
[2] 17357
ssh username@remote
remote> exit
[2]-  Done                    ( sleep 1; nc localhost 6666 > /tmp/file )
local> cat /tmp/file
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
...

Or, more often you want to go the other direction, for example if you want to do something like transfer your ~/.ssh/id_rsa.pub file from your local machine to the ~/.ssh/authorized_keys file of the remote machine.

local> ssh username@remote
remote> ~C
ssh> -R5555:localhost:5555
remote> ~^Z
[suspend ssh]
[1]+  Stopped                 ssh username@remote
local> nc -l 5555 < ~/.ssh/id_rsa.pub &
[2] 26607
local> fg
ssh username@remote
remote> nc localhost 5555 >> ~/.ssh/authorized_keys
remote> cat ~/.ssh/authorized_keys
ssh-rsa AAAAB3NzaC1yc2ZQQQQBIwAAAQEAsgaVp8mnWVvpGKhfgwHTuOObyfYSe8iFvksH6BGWfMgy8poM2+5sTL6FHI7k0MXmfd7p4rzOL2R4q9yjG+Hl2PShjkjAVb32Ss5ZZ3BxHpk30+0HackAHVqPEJERvZvqC3W2s4aKU7ae4WaG1OqZHI1dGiJPJ1IgFF5bWbQl8CP9kZNAHg0NJZUCnJ73udZRYEWm5MEdTIz0+Q5tClzxvXtV4lZBo36Jo4vijKVEJ06MZu+e2WnCOqsfdayY7laiT0t/UsulLNJ1wT+Euejl+3Vft7N1/nWptJn3c4y83c4oHIrsLDTIiVvPjAj5JTkyH1EA2pIOxsKOjmg2Maz7Pw== username@local

A little bit of explanation is in order.

The first step is to open a LocalForward; if you don't already have one established then you can use the ~C escape character to open an ssh command line which will give you the following commands:

remote> ~C
ssh> help
Commands:
      -L[bind_address:]port:host:hostport    Request local forward
      -R[bind_address:]port:host:hostport    Request remote forward
      -D[bind_address:]port                  Request dynamic forward
      -KR[bind_address:]port                 Cancel remote forward

In this example I establish a LocalForward on port 6666 of localhost for both the client and the server; the port number can be any arbitrary open port.

The nc command is from the netcat package; it is described as the "TCP/IP swiss army knife"; it is a simple, yet very flexible and useful program. Make it a standard part of your unix toolbelt.

At this point nc is listening on port 6666 and waiting for another program to connect to that port so it can send the contents of /etc/passwd.

Next we make use of another escape character ~^Z which is tilde followed by control-Z. This temporarily suspends the ssh process and drops us back into our shell.

One back on the local system you can use nc to connect to the forwarded port 6666. Note the lack of a -l in this case because that option tells nc to listen on a port as if it were a server which is not what we want; instead we want to just use nc as a client to connect to the already listening nc on the remote side.

The rest of the magic around the nc command is required because if you recall above I said that the ssh process was temporarily suspended, so the & will put the whole (sleep + nc) expression into the background and the sleep gives you enough time for ssh to return to the foreground with fg.

In the second example the idea is basically the same except we set up a tunnel going the other direction using -R instead of -L so that we establish a RemoteForward. And then on the local side is where you want to use the -l argument to nc.

The escape character by default is ~ but you can change that with:

 -e escape_char
         Sets the escape character for sessions with a pty (default: ‘~’).  The escape character is only recognized at the beginning of a line.  The escape character followed by a dot
         (‘.’) closes the connection; followed by control-Z suspends the connection; and followed by itself sends the escape character once.  Setting the character to “none” disables any
         escapes and makes the session fully transparent.

A full explanation of the commands available with the escape characters is available in the ssh manpage

ESCAPE CHARACTERS
     When a pseudo-terminal has been requested, ssh supports a number of functions through the use of an escape character.

     A single tilde character can be sent as ~~ or by following the tilde by a character other than those described below.  The escape character must always follow a newline to be interpreted
     as special.  The escape character can be changed in configuration files using the EscapeChar configuration directive or on the command line by the -e option.

     The supported escapes (assuming the default ‘~’) are:

     ~.      Disconnect.

     ~^Z     Background ssh.

     ~#      List forwarded connections.

     ~&      Background ssh at logout when waiting for forwarded connection / X11 sessions to terminate.

     ~?      Display a list of escape characters.

     ~B      Send a BREAK to the remote system (only useful for SSH protocol version 2 and if the peer supports it).

     ~C      Open command line.  Currently this allows the addition of port forwardings using the -L, -R and -D options (see above).  It also allows the cancellation of existing remote port-
             forwardings using -KR[bind_address:]port.  !command allows the user to execute a local command if the PermitLocalCommand option is enabled in ssh_config(5).  Basic help is avail‐
             able, using the -h option.

     ~R      Request rekeying of the connection (only useful for SSH protocol version 2 and if the peer supports it).

回答4:

Using ControlMaster (the -M switch) is the best solution, way simpler and easier than the rest of the answers here. It allows you to share a single connection among multiple sessions. Sounds like it does what the poster wants. You still have to type the scp or sftp command line though. Try it. I use it for all of my sshing.

回答5:

In order to do this I have my home router set up to forward port 22 back to my home machine (which is firewalled to only accept ssh connections from my work machine) and I also have an account set up with DynDNS to provide Dynamic DNS that will resolve to my home IP automatically.

Then when I ssh into my work computer, the first thing I do is run a script that starts an ssh-agent (if your server doesn't do that automatically). The script I run is:

#!/bin/bash

ssh-agent sh -c 'ssh-add < /dev/null && bash'

It asks for my ssh key passphrase so that I don't have to type it in every time. You don't need that step if you use an ssh key without a passphrase.

For the rest of the session, sending files back to your home machine is as simple as

scp file_to_send.txt your.domain.name:~/

回答6:

Here is a hack called ssh-xfer which addresses the exact problem, but requires patching OpenSSH, which is a nonstarter as far as I'm concerned.

回答7:

Here is my preferred solution to this problem. Set up a reverse ssh tunnel upon creating the ssh session. This is made easy by two bash function: grabfrom() needs to be defined on the local host, while grab() should be defined on the remote host. You can add any other ssh variables you use (e.g. -X or -Y) as you see fit.

function grabfrom() { ssh -R 2202:127.0.0.1:22 ${@}; };
function grab() { scp -P 2202 $@ localuser@127.0.0.1:~; };

Usage:

localhost% grabfrom remoteuser@remotehost
password: <remote password goes here>
remotehost% grab somefile1 somefile2 *.txt
password: <local password goes here>

Positives:

• It works without special software on either host beyond OpenSSH
• It works when local host is behind a NAT router
• It can be implemented as a pair of two one-line bash function

Negatives:

• It uses a fixed port number so:
  • won't work with multiple connections to remote host
  • might conflict with a process using that port on the remote host
• It requires localhost accept ssh connections
• It requires a special command on initiation the session
• It doesn't implicitly handle authentication to the localhost
• It doesn't allow one to specify the destination directory on localhost
• If you grab from multiple localhosts to the same remote host, ssh won't like the keys changing

Future work: This is still pretty kludgy. Obviously, it would be possible to handle the authentication issue by setting up ssh keys appropriately and it's even easier to allow the specification of a remote directory by adding a parameter to grab()

More difficult is addressing the other negatives. It would be nice to pick a dynamic port but as far as I can tell there is no elegant way to pass that port to the shell on the remote host; As best as I can tell, OpenSSH doesn't allow you to set arbitrary environment variables on the remote host and bash can't take environment variables from a command line argument. Even if you could pick a dynamic port, there is no way to ensure it isn't used on the remote host without connecting first.

回答8:

You can use SCP protocol for tranfering a file.you can refer this link

http://tekheez.biz/scp-protocol-in-unix/

回答9:

You should be able to set up public & private keys so that no auth is needed.

Which way you do it depends on security requirements, etc (be aware that there are linux/unix ssh worms which will look at keys to find other hosts they can attack).

I do this all the time from behind both linksys and dlink routers. I think you may need to change a couple of settings but it's not a big deal.

回答10:

Use the -M switch.

"Places the ssh client into 'master' mode for connection shar-ing. Multiple -M options places ssh into ``master'' mode with confirmation required before slave connections are accepted. Refer to the description of ControlMaster in ssh_config(5) for details."

I don't quite see how that answers the OP's question - can you expand on this a bit, David?