Sandra Henry-Stocker

  • Review

    Book Review: The Book of Inkscape

    Posted November 25, 2009 - 1:02 pm

    Years ago, I discovered Gimp, the free tool that provides Photoshop-like processing of images. Only recently have I come across Inkscape -- the free graphics editor that competes with the likes of Adobe Illustrator. Even you can prepare professional quality graphics if you take the time to learn this fabulous tool. And now here's a book to teach you everything you need to know.
  • Solaris Tip: Have Your Files Changed Since Installation?

    Posted November 18, 2009 - 2:16 pm

    One way to check the integrity of files on your Solaris systems is by comparing their ownership, sizes and checksums against their original values. You don't need expensive application software to do basic integrity checking. One easy and free way to do this is to take advantage of a file that your system maintains on your behalf and a command called pkgchk.
  • Looping the Easy Way

    Posted November 11, 2009 - 1:51 pm

    One of the nice things about writing a column every week is that I don't often have to tackle the really big issues -- such as why Unix is still the best OS or which big company is buying which other big company and how this is going to affect all of us. Instead, I can hone in on an issue as small and personal as how you loop through a sequence of values in a script. Speaking of looping, I've just learned (and then implemented) a new trick.
  • Unix Tip: Grepping on Whole Words

    Posted November 3, 2009 - 6:55 pm

    If every time you grep for a specific word or string, you get a pile of lines that don't match what you were looking for, maybe it's time to learn about whole word searching. In today's column, we examine two ways to get what you want, the whole of what you want and nothing but what you want.
  • Is Your Web Site Under Attack?

    Posted October 26, 2009 - 7:24 pm

    If you have a web site, the answer is undoubtedly "yes". Someone somewhere or, more likely, quite a few someones are attempting to attack your site or the system on which it is running. Assuming hackers have found your site and are testing it for holes that they might crawl through, let's take a look at how you can uncover evidence of their exploits with a quick examination of your web logs.
  • Easy Email Filtering with Procmail

    Posted October 21, 2009 - 1:13 pm

    Tossing email into the /dev/null bit bucket is fine when you know the account in question will never receive any valid form of email. You can, however, get a much finer degree of control over email and still automate the cleanup of spam by using a tool such as procmail. Procmail is a basic email filter and not nearly as difficult to set up as people imagine. Let's run through the setup and focus on a couple potential stumbling blocks.
  • Eradicate Spam from Unix Service Accounts!

    Posted October 13, 2009 - 3:25 pm

    There are numerous ways to reduce the amount of spam that you receive. Good email filters can keep you from ever having to deal with the onslaught of stupid offers you never wanted to see, never mind the outright attempts to steal personal information or rope you into some type of scam. I've found that the spammers have become so desperate to increase their spam traffic deliveries that they are sending spam to system accounts such as bin and listen. Instead of trying to bounce this mail back to the senders -- which in less perverted times might have actually worked, I find it's speedier and less consuming of system resources to just pitch the mail into the bit bucket. Here's how this works.
  • Putting Text in Window Title Bars

    Posted October 6, 2009 - 7:59 pm

    In last week's post, I talked about customizing prompts to help remind your users what system they're logged into and where they are in the file system. Another useful way to help your users keep which window is which straight in their minds is to label the windows themselves. With the system name or project identifier displayed on the title bars of their windows, your users are less likely to type a command meant for system A on the command line for system B.
  • Unix Holidays

    Posted September 22, 2009 - 2:23 pm

    In honor of Eid al-Fitr -- three days that mark the end of Ramadan (a month of fasting and reflection) and my daughter's birthday, I thought I'd take a look at how Unix handles holidays. Think it doesn't? If you're using Solaris, take a look in /etc/acct for a file named "holidays".
  • Checking the Status of Your NICs

    Posted September 15, 2009 - 6:21 pm

    Sun's BigAdmin System Administration Portal provides an extremely useful tool for reporting the status of your network interface cards. Using ifconfig and a seriesof ndd (get driver parameter) and kstat (display kernal statistics) commands, the script prepares a summary of the network interface settings in table form.
  • The Day that Cron Stood Still

    Posted September 11, 2009 - 1:37 pm

    I was surprised a couple days ago to notice that a cron job that was set up to move files from one system to another suddenly stopped working. Squeezing a little timefrom my other tasks to keep the files flowing to the application that needed them, I noted that I could run the script and move the files by hand. In fact, everything ran normally when I did and the files arrived at their proper destination in time to be processed and turned into useful graphs. Even so, the next day, the same thing happened again.
  • Relaying Mail from Subdomains

    Posted September 8, 2009 - 3:06 pm

    Relaying mail doesn't only come into play when someone is trying to use your mail server to deliver mail to a third domain. It can also affect your own subdomains.
  • Review

    Book Review: The Art of Deception: Controlling the Human Element of Security

    Posted September 2, 2009 - 9:56 am

    If I had only one thing to say about The Art of Deception, it would be that it convinced me that even technologically savvy people fall prey to the guile of practiced social engineers (formerly known as a "con artists" to most of us).
  • You're nobody until ...

    Posted August 26, 2009 - 10:48 am

    The old song continues "somebody loves you", the geekier version changes this to "somebody quotes you" and the NFS version claims "somebody trusts you". Whether files in your NFS mounts list "nobody" as the owner and "nobody" as the group or show root and real usernames depends on your NFS settings.
  • Getting help with scat

    Posted August 18, 2009 - 1:47 pm

    Since we looked at mdb last week and probed into a core dump, we should take a quick look at another tool for analyzing core dumps. The "scat" tool provides an easy way to extract an extensive amount of information from a core dump and provide it to you in a relatively readable fashion (as readable as data from a core dump is ever likely to be). Once you start the tool, you can get some help figuring out what commands to use.
  • Probing into Core Dumps with mdb

    Posted August 12, 2009 - 2:19 pm

    The Solaris Modular Debugger (mdb) is a debugger that was designed for low-level debugging -- examining the running kernel or looking into core files and using assembly language know how to figure out what was happening at the time of a system crash. Core dumps are similar in concept to the flight recorders on commercial airplanes. Because they contain the contents of memory at the time of the crash, you can ask just about question you might want to ask about that fatal system moment, but you have to be a very savvy systems geek to know what questions to ask and to understand the answers.
  • Setting up sudo, part 2

    Posted July 28, 2009 - 7:14 pm

    In my July 22nd posting, I promised to provide some more examples of sudoer file entries. Some of these files contain only a few settings -- maybe allowing one or two people to run only a single command or any command with the authority of root -- or they may define groups of users, groups of systems and groups of commands and use these groupings to define how blocks of privileges are assigned.
  • Serial numbers in zone files: Yours and named's

    Posted July 27, 2009 - 5:55 pm

    Serial numbers in zone files help your DNS service determine when it should re-ingest your zone files or ignore them. But there's more to these pseudo timestamps than meets the eye. In fact, the number that you put in your file and the one that DNS extracts from it might be as different as 200907270001 and 3338774385.
  • Setting up sudo

    Posted July 22, 2009 - 3:49 pm

    System administrators are generally very protective of superuser access, as they should be. Root access in the hands of anyone who doesn't fully understand what they're doing is a dangerous thing. Root access in the hands of someone well versed with Unix is bad enough -- we all make mistakes. At the same time, your users can become overly dependent on you if they can't issue any commands as root. Some developers, for example, really need to be able to reboot the systems on which they do development and it isn't necessarily a good thing if they have to wait for you to come back from lunch.
  • Unix Wizdumb: Document It!

    Posted July 15, 2009 - 3:35 pm

    One of the failures that many (if not most) sysadmins exhibit is a failure to document the changes they make or the reasons for particular configuration settings. Many of us have the mistaken belief that, 1) a few years from today, we will still remember what we did today and why and that 2) no one else will ever need to figure out what we did.
  • Unix Wizdumb: Clean up empty "in use" files with "cat /dev/null"

    Posted July 8, 2009 - 6:54 pm

    Ever run into the problem of a 100% full /var file system? Who hasn't? It's so tempting to whip out the old rm command and start cleaning out files. But what if you remove a file that's eating a huge chunk of space only to find that none of the space is freed up? Oops!
  • Unix: Impossible File Types

    Posted July 1, 2009 - 3:27 pm

    In spite of its long history as one of the tried and true Unix commands, even the tar command can offer some surprises. My first encounter with "impossible file type" errors took place earlier today.
  • Unix: Adding swap space on the fly

    Posted June 24, 2009 - 9:02 pm

    Swap space can be critical to the performance of a Unix system. Even if you think you have sufficient memory (1-2 GB), you might find that the demands on your system cry out for more. You can resolve a swap space shortage in a pinch if you have an unused partition on your disk or just extra disk space on a mounted drive.
  • Review

    Network Know-How: An Essential Guide for the Accidental Admin

    Posted June 17, 2009 - 7:51 pm

    If you find yourself getting calls from all your neighbors just because you're a systems geek and can pull a network together in your sleep, here's a great source of fundamental network know how that you might recommend.
  • So many passwords, so few hiding places

    Posted June 10, 2009 - 3:40 pm

    Maybe so, but the hiding places are getting so much better! Let's take a look at what technology hath wrought for solving this age old problem.
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