Letters to the Editor
I am a subscriber to LJ and, in fact, have every issue. I hesitate to say this, because it sounds like so much bullshit, but I have always been impressed by how quickly LJ came up to speed with quality articles. As a Unix applications programmer, I read several periodicals, and I find your nuts-and-bolts approach refreshing, compared to DDJ's articles. However, I am writing (if that is what this form of communication is properly called) to ask for an improvement in LJ. Would your editorial staff please give serious consideration to including articles on FreeBSD? Especially since it poses no threat to the sales of Linux. Furthermore, I think it would increase your sales, at least with some of the programmers that I know.
An informal survey made back in LJ's early days suggested the FreeBSD community wasn't interested in a magazine devoted to FreeBSD, which SSC was contemplating. (Perhaps things have changed?)
As far as giving time to FreeBSD within the pages of Linux Journal, we do have some ideas we're working on. Right now, though, we've got more material about Linux than we can print.
The July '96 issue of LJ presents the new Korn shell (ksh93). What is not mentioned (and is not widely known) is users not interested in commercial support can get Linux, Sun, etc. binaries for free (src is not available). This includes not only the ksh binary but also shared libraries and the Tksh extension for Tcl/Tk. Just check the URL www.research.att.com/orgs/ssr/book/reuse. By the way, the book that URL refers to (Practical Reusable Unix Software, Krishnamurthy, Wiley 1995), is a gold mine, describing and providing the source code for gems such as the dot tool. Dot is a directed graph layout tool, and now I can't live without it. Recommended.
—Alexandre Valente Sousa email@example.com
Mike Loukides and Andy Oram point out in their “Getting to Know gdb” article (September '96) that gdb is capable of setting hardware watchpoints on “only a few workstations”. Not only does the i386 (and beyond) have these capabilities, but current versions of Linux (1.2.1+) and gdb (4.14+) are able to use this feature.
The 386 supports up to four simultaneous hardware watchpoints which can trigger when a memory location is “accessed” (read or written). In Linux gdb, these are the “rwatch” and “awatch” commands. Both commands take an expression to be watched. As the authors point out, this feature is great for watching a memory location that is being mysteriously trashed. The advantage with hardware watchpoints is your program runs at full speed instead of being slowly single-stepped.
The one tricky point in dealing with these watchpoints is they are disabled automatically if program control transfers outside the scope of the expression. For example, if “i” is an automatic variable (a “local” variable), then when a subroutine is called, the meaning of “i” is lost. The workaround is to watch a raw memory location:
(gdb) print &i $1 = (int *) 0xbffffd2c (gdb) awatch *((int *) 0xbffffd2c) Hardware access(read/write) / watchpoint 3: *(int *) 3221224748 (gdb) cont Continuing. Hardware access(read/write) / watchpoint 3: *(int *) 3221224748 123 *foo = 0; (gdb)
—Andy Vaught firstname.lastname@example.org
I couldn't believe it—not one, not two, but three (!) issues of Linux Journal in my mail box Wednesday.
I don't know how to thank you for the happy hours I have wiled away in the past two days. I spent several hours just reading ads.
Not since the old days of Byte magazine can I remember enjoying a magazine's ads so much.
—Dwight Johnson email@example.com
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!
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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