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
firstname.lastname@example.org: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.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide