The 101 Uses of OpenSSH: Part I
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
email@example.com:path/filenameFor 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.
|Using tshark to Watch and Inspect Network Traffic||Aug 31, 2015|
|Where's That Pesky Hidden Word?||Aug 28, 2015|
|A Project to Guarantee Better Security for Open-Source Projects||Aug 27, 2015|
|Concerning Containers' Connections: on Docker Networking||Aug 26, 2015|
|My Network Go-Bag||Aug 24, 2015|
|Doing Astronomy with Python||Aug 19, 2015|
- Using tshark to Watch and Inspect Network Traffic
- Problems with Ubuntu's Software Center and How Canonical Plans to Fix Them
- Concerning Containers' Connections: on Docker Networking
- A Project to Guarantee Better Security for Open-Source Projects
- Where's That Pesky Hidden Word?
- Firefox Security Exploit Targets Linux Users and Web Developers
- My Network Go-Bag
- Doing Astronomy with Python
- Build a “Virtual SuperComputer” with Process Virtualization
- diff -u: What's New in Kernel Development