Linux System Administration: A User's Guide
The reason for a good password goes right back to my description of the password file earlier in the book, specifically as it relates to the password field in nonshadow files. Here's a quick reminder of the format:
The password field (field 2) is encoded by virtue of a hashing algorithm. If you are curious as to the gory details, type <@cxb>man crypt<@$p> and you'll find everything you ever wanted to know about encoding passwords. The short form is this: that strange password is actually a coded version of your password based on a two-character, randomly generated salt. This salt is then used to seed the hashing routine to generate the final group of characters.
The term hashing represents a technique for taking a string of characters (a person's last name, for instance) and generating a unique key (ideally) for easy retrieval of the information from a database. What you are doing is encoding the normal text into a shorter, (usually) numeric representation.
Password crackers figure out passwords by using that salt to generate passwords against every word in the dictionary. While this sounds pretty complex, it's not. A simple program calls the crypt routine, runs the hash on a word and then compares it to the password entry in the /etc/passwd file. If it matches, bingo! They have your password. If it doesn't, they move on to the next word. On a reasonably punchy system, it doesn't take all that long for crackers to work their way through every password in the book.
Don't believe me? Take a look at the output in Figure 1 from a little program called Nutcracker, a freeware tool that does the kind of brute-force password checking I was talking about.
As you can see in Figure 1, picking something you'll remember easily because it is a common word is a bad choice for a password.
Have a look at what happens when I log in to a machine. Everything looks normal. I have a login name, a request for my password. I enter the password and voilà, I am in. But hold on—read that little one-line message that appears after I enter the password:
login: mgagne Password: Last login: Mon Jan 8 16:00:39 from energize
What the heck is “energize”? Energize is the hostname of the computer from which I last logged in apparently, except I don't have a system called energize. Furthermore, let's pretend that I don't know anyone with that system and I always log in from the same place. The only explanation is that somebody from a system called energize logged in to the server with my login name and password.
This is just a hypothetical situation, but it does illustrate one other habit that you should consider training your users to adopt. If they are logging in from the same PC day in and day out, that message should never change. If they do not recognize the hostname in the last login message, they should make it a policy to alert you.
Security isn't just the domain of the system administrator. After all, you've got plenty on your hands. Any help is appreciated. You need to get the users involved. Let them know that system security is their business as well as yours.
Marcel Gagné (email@example.com) is president of Salmar Consulting, Inc., a systems integration and network consulting firm and the author of Linux System Administration: A User's Guide, published by Addison-Wesley.
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.
Free to Linux Journal readers.Register Now!
- Google's SwiftShader Released
- Interview with Patrick Volkerding
- SUSE LLC's SUSE Manager
- My +1 Sword of Productivity
- Tech Tip: Really Simple HTTP Server with Python
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Non-Linux FOSS: Caffeine!
- Managing Linux Using Puppet
- SuperTuxKart 0.9.2 Released
- Returning Values from Bash Functions
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
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