The 101 Uses of OpenSSH: Part I

 in
Mick scratches the surface of ssh.
Using scp for Encrypted File Transfers

We'll cover one more ssh topic before we adjourn for this month. The scp command, in most ways equivalent to the old rcp utility, is used to copy a file or directory from one host to another. (In fact, scp is based on rcp's source code.) In case you're unfamiliar with either, they're noninteractive: each is invoked with a single command line, in which you must specify the names and paths of both of what you're copying and where you want it to go.

This noninteractive quality makes scp a bit less user-friendly than ftp: like it or not, to use scp you need to read its man page (or articles like this) and memorize a few flags. But like most other command-line utilities, scp is far more useful in scripts than interactive tools tend to be. Using scp “on the fly”, though, is easy to learn. The basic syntax of the scp command is

scp [ options ] sourcefilestring destfilestring

where the source and destination file strings can either be a normal UNIX file/path string (e.g., "./docs/hello.txt", "/home/me/mydoc.txt", etc.) or a host-specific string in the format

username@remote.host.name:path/filename
For example, suppose you're logged into the host “crueller” and want to transfer the file “recipe” to your home directory on the remote host “kolach”. Suppose further that you've got the same user name on both systems. The session would look something like this (user input in bold):
crueller: > scp ./recipe kolach:~
mick@kolach's password: *******
recipe         100% |**************>| 13226    00:00
crueller: >
After typing the scp command line, we were prompted for our password (our username, since we didn't specify one, was automatically submitted for us using the username we're logged on to crueller as). scp then copied the file over, showing us a handy progress bar as it went along. And that's it!

Suppose you're logged on to crueller as “mick” but have the username “mbauer” on kolach and wish to write the file to kolach's directory data/recipes/pastries. Then our command line would look like this:

crueller: > scp ./recipe mbauer@kolach:/data/recipies/pastries/

Now let's switch things around. Suppose we want to retrieve the file /etc/oven.conf from kolach (we're still logged in to crueller). Then our command line looks like this:

crueller: > scp mbauer@kolach:/etc/oven.conf.
Get the picture? The important thing to remember is that the source must come before the destination.

Although most users use ssh and scp for simple logins and file transfers, respectively, this only scratches the surface of what ssh can do. Next month we'll examine how RSA and DSA keys can be used to make ssh transactions even more secure, how “null-passphrase” keys can allow ssh commands to be included in scripts, how to cache ssh credentials in RAM to avoid unnecessary authentication prompts and how to tunnel other TCP services through an encrypted ssh connection.

Resources

Mick Bauer (mick@visi.com) is security practice lead at the Minneapolis bureau of ENRGI, a network engineering and consulting firm. He's been a Linux devotee since 1995 and an OpenBSD zealot since 1997, taking particular pleasure in getting these cutting-edge operating systems to run on obsolete junk. Mick welcomes questions, comments and greetings.

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thanks

joviton's picture

god bless you for taking trouble in writing this tutorial of SSH .
linux is the best OS ever .

Linux

Misafir's picture

Linux Where the on World Wide should look

Using SSH

Mithilesh's picture

Hi,

I am new and today used the SSH first time then i thought to study more about SSH and googled the uses of SSH and found your website its very helpfull but still i am unable to understand few things can yu suggest me any good site/article for a new user. I wanted to use this just because it is fast and i love it.

about ssh

Rakesh's picture

sir
I read your article The 101 Uses of OpenSSH: Part I
it boost me to start doing experiments with ssh. it gives me all the basic as i am new bie to it.
But I had one problem i tried to uninstall ssh from my system to install new one using rpm -e option -> It not worked.
I knew (through net searching)the new intallation overwrite the old one, but i want to remove it and install it on my system(redhat-9).
Please can you suggest anything regarding this.

thanking you.

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