Unix as a Second Language

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Sandra Henry-Stocker has been administering Unix systems for more than 25 years. She describes herself as "USL" (Unix as a second language) but remembers enough English to write books and buy groceries. She currently works for TeleCommunication Systems -- a company that builds innovative technologies to make critical connections happen -- where no one else necessarily shares any of her opinions. This blog offers advice for everyday Unix systems administration and some clever ways to approach more challenging problems. Send comments and suggestions to mailto:bugfarm@gmail.com.

by Sandra Henry-Stocker

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  • Unix: Rewriting history

    Posted Jun 16, 2013 - 03:35 pm

    The history feature in Unix shells can save you a lot of time when typing long, fairly repetitious commands, but don't count on it to accurately represent history.
    .bash_profile, bash

  • Unix How To: Sed & Awk -- Still friendly after all these years

    Posted Mar 10, 2010 - 04:45 pm

    Even after decades of using Unix on thousands of systems, I find that it's still fun to discover various convolutions of sed and awk commands to perform command line wizardry. There's a lot more to each of these tools than those uses I make of these commands on a routine basis. Let's take a look at some one-liners you might not yet have tried.
    awk, one-liners

  • Unix tip: Making do with less

    Posted May 20, 2009 - 12:26 pm

    Know the less command? Really know the less command? If you don't use it routinely, you might be surprised at how many things this modest little command can do.
    head, less command

  • Squeezing out the white space

    Posted Oct 29, 2008 - 11:22 am

    Ever need to clean up some sloppy text? You can squeeze out extra white space with some very simple Perl commands. Let's take a look at how this works.
    Perl, Sandra Henry-Stocker

  • Port Knocking

    Posted Mar 03, 2010 - 11:20 am

    Fred Stluka from Bristle.com just introduced me to port knocking -- a method of opening ports on a firewall by trying to connect with a series of ports in a pre-determined order. The sequence of "knocks" acts like a secret access code -- like tapping out the first couple of bars from your favorite song to tell someone inside that it's you. Similar secret taps were used during Prohibition to ensure that only those who knew the secret knock would be allowed into the speakeasies. These days, port knocking provides a way to forge access through a firewall by using the code.
    firewall access, iptables

  • Linux commands: Newusers adds new users ... fast and furious!

    Posted May 14, 2013 - 11:39 am

    Whether you're setting up accounts for existing users on a new server or providing accounts for a crop of new staff members on your primary server, it's nice to be able to do the job quickly and accurately. The newusers command in Linux is designed to make this process as smooth as possible, but it may not do everything you expect -- especially if your data file is, uh, sloppy. Let's take a look at what it does and where it might fall short of expectations.
    accounts, Group

  • Unix How-To: Counting Anything

    Posted Sep 15, 2010 - 11:23 am

    A reader recently asked whether it was possible on Unix systems to count how many times a particular character appears on each line of text. "On Unix", I answered, "not only is just about anything possible, but there are usually half a dozen ways to do it".
    awk, count characters

  • Using prtdiag to troubleshoot system problems

    Posted Oct 15, 2008 - 05:00 am

    Those amber warning lights on your servers are trying to tell you something. Want to know what they're trying to tell you? Take a look at the output of the "prtdiag -v" command and you might learn more about your system than you knew could be known.
    diagnostics, fault

  • How to do a risk assessment for ISO 27001

    Posted Jul 15, 2012 - 02:26 pm

    A key element in the ISO 27001 certification process is to identify and assess risks. While this idea may seem obvious, you may be surprised at how much you can learn about your systems, processes and security threats by pushing them through this very systematic process.
    assessment, control

  • Unix Tip: Avoiding the Oops

    Posted Aug 11, 2010 - 07:32 pm

    Ever type "rm -rf dirname" and then realize you've just blown away the wrong directory? You can always alias the rm command to "rm -i", but let's look at a way that you can selectively determine which directories get that special "Are you sure you want to do that" treatment and which get quietly blown away.
    -i option, protect directories

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