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  • Python script won't write data when ran from cron

    - by Ruud
    When I run a python script in a terminal it runs as expected; downloads file and saves it in the desired spot. sudo python script.py I've added the python script to the root crontab, but then it runs as it is supposed to except it does not write the file. $ sudo crontab -l > * * * * * python /home/test/script.py >> /var/log/test.log 2>&1 Below is a simplified script that still has the problem: #!/usr/bin/python scheduleUrl = 'http://test.com/schedule.xml' schedule = '/var/test/schedule.xml' # Download url and save as filename def wget(url, filename): import urllib2 try: response = urllib2.urlopen(url) except Exception: import traceback logging.exception('generic exception: ' + traceback.format_exc()) else: print('writing:'+filename+';') output = open(filename,'wb') output.write(response.read()) output.close() # Download the schedule wget(scheduleUrl, schedule) I do get the message "writing:name of file;" inside the log, to which the cron entry outputs. But the actual file is nowhere to be found... The dir /var/test is chmodded to 777 and using whatever user, I am allowed to add and change files as I please.

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  • Check connection and reconnect wifi

    - by Ruud
    I'm building a wireless photoframe. The one thing I haven't been able to figure out is how to get my wifi connection back up using a recommended method. Right now I edited /etc/network/interfaces so wlan0 is started at boot: auto wlan0 iface wlan0 inet dhcp wireless-essid ourssid This method works fine for booting. But I found that if I do not check the connection for a long time (could be a week) it might be down. So I should reconnect. What I do now to verify the connection is working is downloading a file from the server that can't be cached (http://server.ext/ping.php?randomize=123456) If I fail to retrieve the file I assume that the connection is no longer working and I run a shell script like #!/bin/bash ifconfig wlan0 up iwconfig wlan0 essid "ourssid" dhclient wlan0 And the connection comes back. But I can't find anything if this is in any way a good method. Can this be improved upon, or is this already right?

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  • How the SPARC T4 Processor Optimizes Throughput Capacity: A Case Study

    - by Ruud
    This white paper demonstrates the architected latency hiding features of Oracle’s UltraSPARC T2+ and SPARC T4 processors That is the first sentence from this technical white paper, but what does it exactly mean? Let's consider a very simple example, the computation of a = b + c. This boils down to the following (pseudo-assembler) instructions that need to be executed: load @b, r1 load @c, r2 add r1,r2,r3 store r3, @a The first two instructions load variables b and c from an address in memory (here symbolized by @b and @c respectively). These values go into registers r1 and r2. The third instruction adds the values in r1 and r2. The result goes into register r3. The fourth instruction stores the contents of r3 into the memory address symbolized by @a. If we're lucky, both b and c are in a nearby cache and the load instructions only take a few processor cycles to execute. That is the good case, but what if b or c, or both, have to come from very far away? Perhaps both of them are in the main memory and then it easily takes hundreds of cycles for the values to arrive in the registers. Meanwhile the processor is doing nothing and simply waits for the data to arrive. Actually, it does something. It burns cycles while waiting. That is a waste of time and energy. Why not use these cycles to execute instructions from another application or thread in case of a parallel program? That is exactly what latency hiding on the SPARC T-Series processors does. It is a hardware feature totally transparent to the user and application. As soon as there is a delay in the execution, the hardware uses these otherwise idle cycles to execute instructions from another process. As a result, the throughput capacity of the system improves because idle cycles are no longer wasted and therefore more jobs can be run per unit of time. This feature has been in the SPARC T-series from the beginning, so why this paper? The difference with previous publications on this topic is in the amount of detail given. How this all works under the hood is fully explained using two example programs. Starting from the assembly language instructions, it is demonstrated in what way these programs execute. To really see what is happening we go down to the processor pipeline level, where the gaps in the execution are, and show in what way these idle cycles are filled by other copies of the same program running simultaneously. Both the SPARC T4 as well as the older UltraSPARC T2+ processor are covered. You may wonder why the UltraSPARC T2+ is included. The focus of this work is on the SPARC T4 processor, but to explain the basic concept of latency hiding at this very low level, we start with the UltraSPARC T2+ processor because it is architecturally a much simpler design. From the single issue, in-order pipelines of this processor we then shift gears and cover how this all works on the much more advanced dual issue, out-of-order architecture of the T4. The analysis and performance experiments have been conducted on both processors. The results depend on the processor, but in all cases the theoretical estimates are confirmed by the experiments. If you're interested to read a lot more about this and find out how things really work under the hood, you can download a copy of the paper here. A paper like this could not have been produced without the help of several other people. I want to thank the co-author of this paper, Jared Smolens, for his very valuable contributions and our highly inspiring discussions. I'm also indebted to Thomas Nau (Ulm University, Germany), Shane Sigler and Mark Woodyard (both at Oracle) for their feedback on earlier versions of this paper. Karen Perkins (Perkins Technical Writing and Editing) and Rick Ramsey at Oracle were very helpful in providing editorial and publishing assistance.

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  • Which programming language suits a system that must work without user input

    - by Ruud
    I'm building a prototype of a device that will function much alike a digital photoframe. It will display images retrieved from the internet. The device must start up and run the photoframe. It will have no user interface. The device has a minimal ubuntu installation, but I could install Xorg or whatever needed. Question: I have trouble figuring out which programming language will be suitable. I've just started using Python to try out several things and I am able to download and display images. I guess that means Python can do what I'd like, but is it suitable as a language that will be run on boot without any user interference? Related questions: - How do I set up Linux to start that script automatically? - How to setup a second Python script as a server that runs in the background to retrieve images before they are displayed (Because I think I'll need threading of some sort?)

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  • Derived template override return type of member function C++

    - by Ruud v A
    I am writing matrix classes. Take a look at this definition: template <typename T, unsigned int dimension_x, unsigned int dimension_y> class generic_matrix { ... generic_matrix<T, dimension_x - 1, dimension_y - 1> minor(unsigned int x, unsigned int y) const { ... } ... } template <typename T, unsigned int dimension> class generic_square_matrix : public generic_matrix<T, dimension, dimension> { ... generic_square_matrix(const generic_matrix<T, dimension, dimension>& other) { ... } ... void foo(); } The generic_square_matrix class provides additional functions like matrix multiplication. Doing this is no problem: generic_square_matrix<T, 4> m = generic_matrix<T, 4, 4>(); It is possible to assign any square matrix to M, even though the type is not generic_square_matrix, due to the constructor. This is possible because the data does not change across children, only the supported functions. This is also possible: generic_square_matrix<T, 4> m = generic_square_matrix<T, 5>().minor(1,1); Same conversion applies here. But now comes the problem: generic_square_matrix<T, 4>().minor(1,1).foo(); //problem, foo is not in generic_matrix<T, 3, 3> To solve this I would like generic_square_matrix::minor to return a generic_square_matrix instead of a generic_matrix. The only possible way to do this, I think is to use template specialisation. But since a specialisation is basically treated like a separate class, I have to redefine all functions. I cannot call the function of the non-specialised class as you would do with a derived class, so I have to copy the entire function. This is not a very nice generic-programming solution, and a lot of work. C++ almost has a solution for my problem: a virtual function of a derived class, can return a pointer or reference to a different class than the base class returns, if this class is derived from the class that the base class returns. generic_square_matrix is derived from generic_matrix, but the function does not return a pointer nor reference, so this doesn't apply here. Is there a solution to this problem (possibly involving an entirely other structure; my only requirements are that the dimensions are a template parameter and that square matrices can have additional functionality). Thanks in advance, Ruud

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  • Problems when trying to connect to a router wirelessly

    - by Ruud Lenders
    The situation - At my girlfriend's parents' place there are six Windows 7 devices that are wired or wireless connected to a router: 3 dekstops and 3 laptops. There are also several smartphones using the router. The router is secured with WPA2 (AES). The problem - We never had any problems with the router for over a year. But recently - about 3 weeks ago - my girlfriend's laptop (HP) and my laptop (ASUS) started to develop problems while trying to connect to the router. The router has stopped showing up from the network list. Sometimes it comes back and shows up, but then it keeps saying something along the lines of "Could not connect", and not long after that it dissapears again. The range of the router is not the problem here, because we experience the same when we sit next to the router. Sometimes, if we are lucky, and waited a long time (10-15 minutes) without using the laptop for anything, the laptop will eventually succesful connect to the router. The attempts - Of course, the Window 7 troubleshooter. We tried troubleshooting the connection problems and the wireless network adapter, but no luck. We also reset the router enough times to know that's not helping either. Here's the full list of things we tried, but did not help: Running the Windows 7 troubleshooter Resetting the router (more than once) Setting the router settings to factory defaults Disconnecting all other devices except one laptop Applying a system restore Trying static/dynamic IP/DNS - Dynamic is better, right? Enabling/disabling IPv6 - Should I keep IPv6 disabled? Running the command: netsh wlan stop hostednetwork Running the command: netsh wlan set hostednetwork mode=disallow Updating/reïnstalling wireless adapter drivers The tests - To help finding the core of the problem, we tested the following: Plugging an ethernet cable in the router and in our laptops - worked fine Connecting someone else's laptop to the router (wireless) - worked fine Connecting our laptops to someone else's router - worked fine The router - This information might be relevant: Router model: Sitecom 300N Wireless Router Router hardware: version 01 The DCHP Server's IPs range from 192.168.0.100 to 192.168.0.200. Router settings: Wireless channel: 12 Channel bandwidth: 20/40 MHz Extension channel: 8 Preamble type: Long 802.11g protection: Disabled UPnP: Enabled The laptops - If you are wondering about our laptops: My laptop model: ASUS Pro64JQ Girlfriend's laptop: HP Pavillion G6 OS: Both Windows 7 Professional x64 - with Service Pack 1 My wireless adapter: Atheros AR9285 AdHoc 11n: Enabled The question - Does anyone have experienced the same problems as I do? Or does someone know how to solve this? Are there more tricks I can try, or settings I should change? Note - Our laptops are not slow or old. My laptop is 1.5 years old, and the other laptop is just 5 months old. I know how to keep laptops clean and I'm pretty sure both laptops are not bloated with useless software.

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  • Xbox Music ignores Asus FN media keys in Desktop Mode

    - by Ruud Lenders
    I have an Asus PRO64JQ laptop, and I recently upgraded to Windows 8. The FN keys stopped working, so I tried to install default drivers using the CD that came with my laptop. Unfortunately, the CD does not support Windows 8. Asus Support does not help me either. It seems that Asus does not support Windows 8 on my model, since I can't find it in their list of Windows 8 upgradable models. Also, the support page of my laptop does not allow me to select Windows 8 as OS. That's why I'm asking my question here. I fixed (most of) the FN keys by installing the ATKPackage, and I was happy to find out that the media keys (play/pauze, next, previous) works with the Xbox Music app. But the keys only work in the Metro UI. In Desktop Mode, pressing FN+? (play/pause) starts up Windows Media Player. Disabling Windows Media Player through the control panel stops it from popping up, but Xbox Music still only responds to them in the Metro UI. I remember that I had similar problems when I tried to make these media keys to work with iTunes on Windows 7. The fix there was a small iTunes plug-in. So tell me, do you know how to fix my problem? Thanks.

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  • Deep insight into the behaviour of the SPARC T4 processor

    - by nospam(at)example.com (Joerg Moellenkamp)
    Ruud van der Pas and Jared Smolens wrote an really interesting whitepaper about the SPARC T4 and its behaviour in regard with certain code: How the SPARC T4 Processor Optimizes Throughput Capacity: A Case Study. In this article the authors compare and explain the behaviour of the the UltraSPARC T4 and T2+ processor in order to highlight some of the strengths of the SPARC T-series processors in general and the T4 in particular.

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  • Two different seeds producing the same "random" sequence

    - by Ruud Lenders
    Maybe there is a very logic explanation for this, but I just can't seem to understand why the seeds 0 and 2,147,483,647 produce the same "random" sequence, using .NET's Random Class (System). Quick code example: ushort len = 8; Random r0 = new Random(0), r1 = new Random(1), r2 = new Random(int.MaxValue); //2,147,483,647 byte[] b0 = new byte[len], b1 = new byte[len], b2 = new byte[len]; r0.NextBytes(b0); r1.NextBytes(b1); r2.NextBytes(b2); for (int i = 0; i < len; i++) { System.Diagnostics.Debug.WriteLine("{0}\t\t{1}\t\t{2}", b0[i], b1[i], b2[i]); } Console.ReadLine(); Output: 26 70 26 12 208 12 70 134 76 111 130 111 93 64 93 117 151 115 228 228 228 216 163 216 As you can see, the first and the third sequence are the same. Can someone please explain this to me?

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  • Store return value of function in reference C++

    - by Ruud v A
    Is it valid to store the return value of an object in a reference? class A { ... }; A myFunction() { A myObject; return A; } //myObject goes out of scope here void mySecondFunction() { A& mySecondObject = myFunction(); } Is it possible to do this in order to avoid copying myObject to mySecondObject? myObject is not needed anymore and should be exactly the same as mySecondObject so it would in theory be faster just to pass ownership of the object from one object to another. (This is also possible using boost shared pointer but that has the overhead of the shared pointer.) Thanks in advance.

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