SSH IV

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SSH IV

Summary:

Copying Files With 'scp'
Copying Files With 'sftp'
Copying Files using 'rsync'
Copying Files Via Tunneled FTP

Copying Files With 'scp'

SSH gives you access to a set of commands and a shell on a remote machine. By itself, it does not enable you to copy files, it however provides the

scp

command.
Say you want to copy a file called 'dumb' from the current directory of the local machine to your home directory on a remote machine called www.foobar.com. Your account name on the remote machine is 'bilbo'. The command would be:

scp dumb bilbo@www.foobar.com:.

To copy it back:

scp bilbo@www.foobar.com:dumb .

'scp' calls SSH to do the login, then it copies the file and then calls SSH again to close the connection.

If your '~~/.ssh/config' already contains a configuration for your account on www.foobar.com like

Host *fbc ~HostName www.foobar.com User bilbo ~ForwardAgent yes

then you can replace 'bilbo@www.foobar.com' with 'fbc':

scp dumb fbc:.

'scp' assumes your home directory on the remote machine to be your current working directory, so if you are using relative paths for the remote machine, they have to be relative to the location of your home directory on that machine.
Using the

-r

switch for 'scp', you can also copy directories recursively. 'scp' also allows you to copy files between remote machines.

Now you might be tempted to try something like this: you open an SSH connection to www.foobar.com. Once you are logged in, you type

scp &#123;local machine&#125;:dumb .

to copy the local file 'dumb' to the remote server you are currently logged in. Most likely you will get a message like

ssh: secure connection to &#123;local machine&#125; refused

What has happened is that you executed the remote version of 'scp', and it tried to connect to an SSH server running on your machine … So remember to run 'scp' always from a local terminal, unless your machine also runs an SSH server.

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Copying Files With 'sftp'

If you prefer a more 'ftp-ish' approach, try sftp (part of the sftp RPM). 'sftp' establishes an SSH tunneled FTP connection to a server and allows you to use most of the standard FTP command set. As an added bonus, 'sftp' allows you to run remote programs via the

exec

command. Since version 2.0.7, the popular graphical FTP client gftp supports sftp-transfers, which makes up for sftp's somewhat limited feature set. In Konqueror you simply type

sftp://serverdomain

into the upper URL line field to use it.

If the remote server doesn't have the sftp server, 'sftpserv', running, just copy the 'sftpserv' executable to your remote home directory (or a directory you have access to and which is included in your remote $PATH). 'sftp' will activate this server automatically upon connect. You'll need no extra permissions on the remote server.

There is a big problem with the usage of sftp on a command line. It is not able to copy also folders inside of other folders recursively. Use scp instead of it.

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Copying Files using 'rsync'

'rsync', the immensely useful tool for copying, updating and removing remote and local files, can most easily be used with SSH by adding the option

-e ssh

. I'm using it myself for MUO ;-).
One of the advantages of 'rsync' is, that it only transfers the differences between two given sets of files. A whole file is only transferred if it is missing at the target location. Furthermore it offers a very efficient method for compressing data and thus makes transfers even faster.
You'll find 'rsync' on your Mandrake CD.

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Copying Files Via Tunneled FTP

If you really insist on using your traditional FTP client, prepare for some fiddling ;-). SSH allows all kinds of protocols to be 'tunneled', FTP too. FTP is a bit of a weird protocol however (e.g. it requires two ports) and results may differ from server to server and from client program to client program. If your FTP client doesn't support connecting to a specified port, you can forget it right away.

The magic word is 'port forwarding'. You forward a non-privileged local port (i.e. usually a port > 1000) to a remote server and then connect to the local machine. Sounds complicated? Well, it is. And I can't be of much help here since I haven't got to getting it working either.
The basic idea is to forward a port, fork SSH into the background and occupying it with a senseless command to keep the channel open:

ssh &#123;user@remote host&#125; -f -L 1234:&#123;remote host&#125;:21 tail -f /etc/motd

Now start an FTP client, and point it at the forwarded port:

lftp -u &#123;user name&#125; -p 1234 localhost

Whereas commands like

cd

are OK, commands like

ls

get

either result in a hanging process or mysterious error messages or both.

There are several programs which try to get around this problem: ftpsshd and hsftp. But all of them are either not working correctly or are too inconvenient to use.

Bottom line: For transferring files, better stick with one of the first three methods.

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Next Item: Tunneling POP, X, VNC ...

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