Configuring pppd in Linux, Part I
It is interesting to notice that minicom itself doesn't have any idea about the at command or the OK response. In fact, minicom's main tasks are very simple: to display the characters that come from the serial port and to send the characters the user keys in through the keyboard to the serial port.
In a sense, the modem is like a robot that talks to the computer using the serial port. That is why using minicom allows you to, in a sense, have your own private conversation with the modem. In the previous section, for example, you sent the modem the string at<Enter>, and the modem responded with the string OK<Enter>.
What kind of conversation can you have with the modem? As a matter of fact, every modem understands the Hayes command set that is based on the at command set. Some manufacturers also offer some very interesting extensions. If you want to find out what they are, all you have to do is look up the commands available for your modem in your modem manual. For example, the commands ATL-1, ATL-2 and ATL-3 are common to every modem; they set the speaker volume to low, medium or high.
Even though you don't need to know many of these commands to use the modem effectively, you might want to try out a few commands to understand a bit more about how your modem works. Remember that it is always possible to type the commands at&f and at&w to reset the modem to the manufacturer's configuration in case you send the modem a few unsafe commands that compromise its configuration and prevent it from connecting.
The command ATDT93355100 is used to dial a number, in this case 93355100. DT stands for dial tone, as opposed to DP, which stands for dial pulse. You might have to use the latter if you live in a rural area and are connected to an analog telephone exchange. Try to send the modem the command ATDT, followed by the number of your internet service provider, to see what happens.
In my case, the connection looks like the one in Figure 3. As you can see, after the hardware handshake (with a lot of whistling on both sides), the modem responds with a nice CONNECT 52500 message, which means the connection was established without any trouble. Of course, there are other messages you may get as a response: NO DIALTONE (there is no phone line attached to the modem), BUSY (the line is engaged), NO ANSWER (there was no answer) and so on (see Figure 4).
In my case, the connection was established successfully and my ISP sent me the cryptic string as soon as I connected (the one that starts with ~}#.!}!±} }4}``}&} }*} } }%). In fact, my ISP is expecting to have a conversation with my PPP dæmon, whereas I am only running minicom, which will show exactly what my ISP would have sent to my PPP dæmon.
It is very important to remember that from now on the modem is going to stop responding to any at commands; all the information sent to the serial port will be modulated and sent to the other side of the line. At the same time, all the information coming from the other side of the line will be demodulated and sent to the serial port (hence, the word modem). The computer (or, better, the serial port) is not aware of all this. It runs exactly as if there was a serial cable running from your computer to the computer on the other side. In fact, if you have two PCs at home, you can network them together quite easily using pppd and connecting their serial ports with a serial cable (you have to make sure it's an inverted cable so that the send pin of the first computer is connected to the receive pin of the second computer, and vice versa).
Next month I'll talk about configuring your computer so that you can connect to the Internet without using any advanced tools. Stay tuned!
Practical Task Scheduling Deployment
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.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- SuperTuxKart 0.9.2 Released
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
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