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Understanding Threads
The traditional Unix model was fork and exec, which is "expensive" in terms of cpu time. However (and this is the part that often gets left out), that doesn't mean that fork and exec is "bad" and threads are "good": it depends upon what it is you need to accomplish. Even at that, there are other considerations, as we shall see.
| Title | Date | Comments | |||
|---|---|---|---|---|---|
| Here files (shell scripting) | 2012 10 | 2012/10/09 TonyLawrence | |||
| - Once again, I've been bitten by not having read the manual recently. This bite really annoyed me. - | |||||
| No clobber scp - scp without overwriting | 2012 10 | 2012/10/07 TonyLawrence | |||
| - Although you usually want scp to update files, there are times when you definitely do not. I wrote this script to avoid overwriting existing files. - | |||||
| Capture and report (Bash Scripting) | 2011 11 | ||||
| - You've been asked to copy some jpg files to a USB disk overnight. That's easy enough - a cron job and a simple 'cp -a' will do that. But there is so much that could go wrong, isn't there? There might not be any files to copy or there might not be room on the USB disk. Somebody might have changed permissions on files or directories alreasdy in place, preventing overwrite with updated images. - | |||||
| Do you hate your computer? | 2011 09 | 2011/09/15 BigDumbDInosaur | |||
| - I knew someone who became so frustrated with a computer printer that he threw it down on the floor and jumped up and down on it until it was smashed to pieces. That's a bit extreme (and damaging to your bank account), but technology can make us feel like that, can't it? - | |||||
| Death of the command line revisited | 2011 09 | 2011/09/10 TonyLawrence | |||
| - Five years ago I wrote a little blurb called Death of the command line. As it happened, that article was misunderstood by many who read it - I don't know if it was my fault or theirs, but somehow many readers ended up thinking I was either predicting the demise of CLI's (Command Line Interfaces) or hoping for that demise or both. Nothing could have been farther from the truth. I remain a big fan of CLI's and use them daily. And yet, just five years later and still at risk of angering yet another batch of folk who won't read carefully, I'm going to suggest that predicting the death of the CLI may not be such a bad bet after all. - | |||||
| Cranky Old Newsgroup Guys | 2011 09 | 2011/10/22 BigDumbDinosaur | |||
| - People new to the Internet may not even understand the difference between a forum and a Newsgroup. Indeed, many may never have participated in any Newsgroup discussions at all. If you have, it may have only been thorough Google Groups, and if your only exposure to the Usenet Newsgroups (with a capital N, yes) has been through that, it can be a little hard to tell the difference between those and a discussion forum. They both have people discussing things, arguing, calling each other idiots and so on. What's the difference? - | |||||
| Email addresses still matter (for now) | 2011 09 | ||||
| - Email: it has helped kill the post office, is the primary source of spam, is critical to many businesses and, after malware, is probably the single largest source of user difficulties. Every internet user has at least one email address and many of us have several. Email is ubiquitous and very important. It's also threatened: many people use services like Facebook and Google+ for most of their daily communication. Somewhat ironically, you typically need an email address to sign up for these services, but the deficiencies of email have even caused some to try to eschew it completely and only use alternatives like those. That trend may continue; in a decade or so, "email" may be as antiquated as "gopher" and "uucp" are today. - | |||||
| Why defragging your computer may be a waste of time | 2011 09 | 2012/12/03 BigDumbDinosaur | |||
| - In fact, defragmenting may be a total waste of time. It's unlikely to be harmful (though it can be if interrupted by a sudden power failure), but it may actually accomplish nothing worth even the minor effort it takes to run it. - | |||||
| Common email problems | 2011 08 | 2011/09/02 ed | |||
| - Yesterday I talked about why you shouldn't send Word attachments in email. Today I'll continue with more attachment related issues and also touch on some other common email glitches. - | |||||
| Why you shouldn't send Word attachments | 2011 08 | 2011/08/31 BigDumbDinosaur | |||
| - As I continued my walk, I thought about how email issues are likely the most common mysteries my neighbors have with their computers. Notice that I said "mysteries" and not "problems". That's because most email issues are from misunderstanding and confusion, not necessarily any real problem. A virus infection is a problem. A dead hard drive is also a problem, but email is usually simple confusion or lack of knowledge. - | |||||
| 10 things - no, 11 things - you say that drive your computer tech person crazy | 2011 08 | 2011/09/20 anonymous | |||
| - Yes, of course people sometimes say or do silly things, even outright stupid things. We all do. Look me straight in the eye and tell me you have never done anything like that with a computer and I'll look you straight in the eye and tell you the same thing and then we'll both try not to laugh. - | |||||
| Switching to Mac OS X - quick tips for new users | 2011 08 | ||||
| - First thing, understand that I'm not going to try to convince to to switch. I f you are stuck in the world of Microsoft, I feel sorry for you, but making you understand that you should switch is not my purpose today. This article is just quick tips for those who have decided to switch. - | |||||
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| A non-technical guide to understanding and fixing TCP/IP problems on a network | 2011 08 | 2011/08/14 BigDumbDinosaur | |||
| - The title is a bit incorrect in the .non-technical. claim, because we are dealing with a geekish subject here and I can't avoid being a little "techie". - | |||||
| Getting Started with Amazon Web Services | 2011 04 | 2011/04/12 TonyLawrence | |||
| - Getting a web site up and running on Amazon Web Services is much easier than it looks. - | |||||
| Tips on Hard Drive Problems | 2011 02 | 2011/03/02 BigDumbDinosaur | |||
| - Back in the 1980's, I could count on earning a few hundred dollars every month from hard disk failures. - | |||||
| Using the shell (Terminal) in Mac OS X | 2002 12 | 2013/01/27 TonyLawrence | |||
| - Many Mac OS X users will not have any need to use the Unix shell that underlies their graphical interface. They are missing out. - | |||||
| Using sudo | 2002 02 | 2013/03/05 lou | |||
| - I'm sure that there are more poorly written man pages, but "man sudoers" (which is how you find out about "sudo") is among my all time favorites for poor explanation. Let's clear that up. - | |||||
| Basic DNS: PTR records and why you care | 2004 07 | 2011/05/02 BigDumbDinosaur | |||
| - A PTR record (sometimes called a "host PTR record") is what lets someone do a "reverse" DNS lookup - that is, they have your IP address and want to know what your host/domain is. - | |||||
| Writing and Compiling C programs on Linux | 2004 12 | 2012/02/10 TonyLawrence | |||
| - Writing and compiling c programs on Linux, common errors for beginners. Most Linux and Unix programs are written in C. When you download source for a project, it will often be C or C++ source code. You don't necessarily need to know a darn thing about C or anything else to compile the source if you aren't changing it. It may be helpful for you to understand a bit if you are having problems with the compile, but even that isn't really necessary. - | |||||
| GPG/PGP Basics | 2001 11 | 2013/04/05 ClovisSangrail | |||
| - Using gpg for encryption, understanding the basic use of GPG for new users. Recently someone asked me for a GPG or PGP public key so that they could send some sensitive material to me by email. - | |||||
| UNIX Basics-JOB SCHEDULING | 2004 05 | 2011/10/29 anonymous | |||
| - Basics of Cron scheduling. In the UNIX or Linux environment, it is possible to asynchronously execute tasks at any desired time of the day, a feature made possible by the cron clock daemon. - | |||||
| Understanding PAM | 2005 03 | 2013/04/18 anonymous | |||
| - PAM is the Pluggable Authentication Module, invented by Sun. It's a beautiful concept, but it can be confusing and even intimidating at first. - | |||||
| Recursive chown | 2006 03 | 2012/08/16 TonyLawrence | |||
| - 'chown -R' is smarter than you think. I had email this morning from someone using "chown" to fix up permissions on a directory. He had discovered "-R" in the man page but had run into a small problem... That succesfully changed the ownership of the "dot" files, but had an unexpected (to him) side effect: /usr was also changed. - | |||||
| Controlling core files (Linux) | 2005 03 | 2011/11/06 TonyLawrence | |||
| - Control Linux core files with ulimit and /proc templates. - | |||||
| Mac Screen sharing is not just for Macs | 2008 01 | 2012/03/22 TonyLawrence | |||
| - Mac Screen Sharing can connect to any VNC host. That's Mac Screen Sharing connecting to a TightVNC server on my wife's Windows XP machine. - | |||||
| Tightvnc, Chicken of the VNC | 2003 10 | ||||
| - Reviews of TightVNC and Chicken of the VNC. VNC is "Virtual Network Computing" and is a crossplatform method of allowing remote access to desktops (Windows or Unix/Linux, Mac and others)). It is conceptually like using Terminal Services or PcAnywhere etc for Windows but is license free and of course capable of serving Linux/Unix machines also. - | |||||
| Numeric Unix Error Messages | 2001 12 | 2010/04/06 TonyLawrence | |||
| - It's an unfortunate fact that many programmers are lazy about error messages. Very often, all you get is a cryptic "Error 5", and you may be lucky to get that. - | |||||
| Routing Basics | 1997 | 2013/04/27 TonyLawrence | |||
| - Network routing basics, understanding TCP/IP routing. So, let's say that 192.168.200.83 is our server, and 192.168.201.35 is a Windows machine. Again, it's a class C netmask (255.255.255.0), so there is going to have to be a router in the network. That router is going to have to have one port on the 192.168.200 network, and one on the 192.168.201 network. - | |||||
| Basics: rsync | 2003 07 | ||||
| - You can learn quite a bit about rsync and how it works right on your own machine. That's actually a good way to learn: it's quick, and you can easily see the results. - | |||||
| Operating System Concepts | 2003 05 | ||||
| - Basic OS concepts. The CPU (Central Processing Unit) is the heart of any computer, but the operating system is the brain. Unfortunately, understanding exactly how these things really work can be difficult, because it's fairly hard to "play" with the operating system that you are actually using. You can do quite a bit with sophisticated debuggers, but eventually you run into confusion and difficulty. And, as you try more complex tasks, you run the risk of interfering with the real machine's operating system. Finally, modern CPU's are very complex, and that complexity can make it more difficult to understand basic concepts. - | |||||
| What is a Managed Switch? | 2005 08 | 2012/07/17 TonyLawrence | |||
| - A managed switch allows you to control the individual ports of your switch - | |||||
| Understanding Floating Point Formats | 2003 09 | 2011/10/28 TonyLawrence | |||
| - Understanding basic floating point. Under ordinary circumstances, you don't have to know or care how numbers are represented within your programs. However, when you are transferring data files that contain numbers, you will have to convert if the storage formats are not identical. If the numbers are just integers, that's fairly easy because the only differences will be the length and the byte order: how many bytes the number takes up, and whether it is stored lsb or msb (least significant byte or most significant byte first). Once you know that, conversion is trivial. - | |||||
| Unix Permissions | 2001 04 | ||||
| - Note: these are classic Unix permissions. However, many modern Unixes support extended attributes that go beyond this. We'll look at one example of that later in the article. - | |||||
| General Trouble Shooting | 2000 08 | 2010/12/24 anonymous | |||
| - Sometimes computer problems can feel like Dickens' dying woman- you know something is wrong, but you have no idea where or how to start looking for it. - | |||||
| Cron At and Batch | 2000 01 | 2012/06/11 TonyLawrence | |||
| - Cron, Batch and At, including explanations of why it might not be working - | |||||
| VPN's and other remote access | 2001 04 | 2011/05/09 TonyLawrence | |||
| - VPN Basics. A VPN is a Virtual Private Network. The concept is that you are using public or other shared lines (generally the Internet) to connect machines, but that all packets are encrypted (so your connections are "private"). - | |||||
| Understanding Device files | 1998 | 2012/08/30 TonyLawrence | |||
| - Unix device files are not like ordinary files. Understanding their properties and use is very helpful. - | |||||
| Floppy Disks | 2001 01 | 2013/03/25 TonyLawrence | |||
| - Unix/Linux Basics Floppy Disks. If you are coming from the Windows world, Unix floppy drives are going to seem really dumb. In Windows, the drive is just there: you pop it open in My Computer, the files are visible, you run the program you want or just drag files off to your hard drive. Simple. - | |||||
| Xinetd | 2003 07 | 2010/10/29 SalvoLtWorfTomaselli | |||
| - Xinetd is a replacement for inetd, which was the original Unix super-daemon used to start network services on demand. The reason for inetd goes back to days of low memory and poor memory management: you didn't want to keep a service running in memory if it was infrequently used. - | |||||
| Unix and Linux startup scripts, Part 1 | 2009 12 | ||||
| - In the beginning, there was "init". If you had a Unix system, you had "init" and it was almost certainly process id 1. - | |||||
| Understanding Packed BCD | 2003 09 | ||||
| - Understanding Packed BCD. Packed BCD (Binary Coded Decimal) is a numeric format that was directly supported on cpu's almost from the beginning, and still is today. Simply put, it relies on the fact that 4 bits are more than sufficient to represent decimal numbers. Therefore, two decimal numbers can be held in each byte, a 32 bit register can hold 8 such numbers, and a 64 bit register can of course hold 16. - | |||||
| Continuation Lines | 2006 06 | 2010/05/27 anonymous | |||
| - There's been a long standing Unix convention of breaking long lines with a "\" to make them easier to read. You'd almost always see this in files like /etc/printcap, but there are plenty of other places where this convention is used. - | |||||
| How can i mount a ISO Image CD ? | 2004 07 | 2010/07/10 TonyLawrence | |||
| - You have an image of a CD or perhaps of a floppy disk and need to mount it as a filesystem (Linux, Mac OS X, BSD, SCO, Solaris). - | |||||
| Why is my system slow? | 2001 12 | 2010/06/11 veera | |||
| - This is not a performance tuning article. If your Linux or Unix system is always slow, this article may not be what you are looking for. - | |||||
| Simple XML POST and reply | 2010 03 | 2010/03/24 TonyLawrence | |||
| - A customer has an app that needs to post and get XML data from a website. This task was being handled by .asp scripts on a Windows box, but now they want it moved to Linux and Perl. - | |||||
| Understanding Serial Wiring | 1992 | ||||
| - I have seen intelligent adult human beings brought to the very edge of insanity by the (anticipated) simple connection of a terminal or a serial printer to a Unix system. - | |||||
| Using color in shell scripts (Linux, Mac OS X) | 2009 11 | 2010/01/03 BigDumbDInosaur | |||
| - Color is tricky. Displays can be bad at it, people can be color blind... using colors can make text hard to read - I don't like using color in scripts. - | |||||
| Sort -u vs. uniq | 2009 11 | ||||
| - Don't tie yourself in pipeline knots with either of them; learn to use each of them appropriately and your scripts will be easier. - | |||||
| Understanding Virtual Domains | 2003 07 | ||||
| - Virtual domains can seem confusing at first, but actual it's pretty simple. Here's the basic idea: you have ONE web server, at ONE IP address, but you host multiple websites, each with different content. - | |||||
| Networks 101 | 1998 03 | ||||
| - There are a few fundamental ideas about TCP/IP networks that people seem to get confused about. This article might help. - | |||||
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| Random Numbers | 2003 09 | 2010/07/13 TonyLawrence | |||
| - Understanding Random Numbers. Until fairly recently, cpu's had no direct way to generate random numbers. Intel's Pentium III introduced a hardware random number generator that uses thermal noise "to generate high-quality random and nondeterministic numbers" , but prior to that systems that needed good random numbers had to rely on add-on boards or other external input. - | |||||
| Bash typecasting | 2006 08 | ||||
| - Bash has typecasts - but only sort of and your scripts can easily break because of it - | |||||
| taskset for CPU affinity | 2005 10 | 2012/01/09 TonyLawrence | |||
| - SMP operating systems have choices when it comes to scheduling processes: a new or newly rescheduled process can run on any available cpu. However, while it shouldn't matter where a new process runs, an existing process should go back to the same cpu it was running on simply because the cpu may still be caching data that belongs to that process. - | |||||
| SSH | 2001 05 | ||||
| - Standard Unix tools like telnet and ftp are not encrypted- everything you type, including your precious passwords, travels in packets that can at least potentially be seen by every machine they pass by or through. - | |||||
| Using Tapes and tape drives | 1998 09 | ||||
| - This is an old article about SCO Unix tapes and tape drives and is only left here for historical purposes. - | |||||
| Basic TrueCrypt Usage | 2010 01 | 2010/01/12 TonyLawrence | |||
| - People have said that they installed TrueCrypt, but have no idea what to do next. OK, maybe the interface isn't all that user friendly. - | |||||
| The amazing tool called netcat | 2009 08 | ||||
| - netcat with its simple and yet incredibly powerful command line constructs has helped me innumerable times - | |||||
| Symlinks | 2005 10 | ||||
| - Symlinks is a handy utility for managing symbolic links. It can clean up the sort of problems that come from carelesness when creating symbolic links. - | |||||
| Network Troubleshooting | 2010 03 | 2010/03/16 AndrewSmallshaw | |||
| - As it turned out, the problem was very physical: a light fixture had fallen down and loosened some connections to a long forgotten ethernet switch. - | |||||
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