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• WiFi, No ping, other works fine

  - by Linux Mom

  I installed Ubuntu 12.04 LTS for my mom, this runs OK. However recently, I switched back and forth between encryptions on our WiFi Router from WPA-PSK to WEP and back again to WPA-PSK, same password. Now this old laptop won't even ping the gateway on the router, although the nm-applet shows connected. I tried re-adding the network and putting in the BSSID. I did this over again sometimes just to verify. I tried with my 3G Tethering on my phone, it works fine, can go online too. My other Linux laptop can go on the same wifi as well as my phone. And this laptop used to been online on the same network, same password, same encryption (WPA-PSK) What can be wrong ? Does it need a serious kick in the butt or removing some cached authorisation somewhere?

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• How to set up multiple GPUs (12.04)?

  - by Brother Erryn

  I have two GPUs: one Intel i915 integrated, and one NVIDIA 560 Ti. This is NOT a hybrid setup, nor a laptop. In Windows 7, each card is connected to a different monitor, with the NVIDIA doing any "heavy lifting". For the life of me I cannot get Ubuntu to recognize the i915, but when logging off or rebooting, the shutdown actually appears on the i915. lshw lists both. I'm running the "current" NVIDIA drivers (not the experimental), but Displays calls its monitor a "Laptop". Is this even possible under Ubuntu? The only things that even looked like potential solutions were for laptop hybrid setups and used Bumblebee, but that doesn't seem to apply here.

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• Can't load Wordpress static files on home network

  - by Tosho

  I've just installed Wordpress 3.5 on my laptop (LAMP on Ubuntu 12.10) and when I'm trying to access the site from my phone but it doesn't load static files (css and images). I tried with Opera Mobile Emulator on my laptop and it works perfectly. I also have another Drupal site on my localhost which I can load from my phone without any issues. Both directories have chmod 777 permissions. What can cause that? Just tried to open the site from my sister's laptop but it except static file I can't access any post or page.

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• External hdd boot entries added to GRUB after upgrade to 13.10

  - by Jason

  Long story short, I was using my laptop's internal HDD as an external one on my desktop, and I forgot to remove it when I was upgrading to 13.10. Now GRUB on my desktop has added entries for the Windows and Ubuntu partitions that exist on the laptop's HDD, but I don't want them to be there. Can I safely remove them ? My GRUB table looks like this if I recall correctly: Ubuntu Advanced Options (or something like this) Memtest Another Memtest Entry Windows 7 (loader) on /dev/sda1 Windows 7 (loader) on /dev/sdb1 Ubuntu 13.04 Advanced Options for Ubuntu 13.04 Where Windows 7 (loader) on /dev/sdb1 Ubuntu 13.04 Advanced Options for Ubuntu 13.04 are the entries from the external/laptop's HDD.

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• No sound/audio after resuming from sleep

  - by hansvonaachen

  I've made a fresh UEFI install of Ubuntu 13.10 (64 bit) on a Lenovo Ideapad Z510 laptop with Intel i5 4200M processor. Ubuntu is the only OS installed on the computer, secure boot disabled. Everythings works fine (backlight issue fixed after editing rc.local file), the only minor trouble I have is resuming the laptop from "sleep" mode. If I close the lid and then wake the laptop opening it again, there is no audio/sound. I need to restart the computer (not even logging out helps). If I suspend the computer in a graphical way (not closing the lid): gearwheel in top right of the screen -- suspend and wake it up/turning on, audio works with no issues. Ideas how to fix this? Thanks!

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• Ubuntu 12.4 not listed while in boot menu

  - by radkrish

  I am using Dell Inspiron 17R with Windows7 as the primary OS to boot my system up. I am new to Linux and to begin with, I thought of installing Ubuntu 12.4 AMD 64 bit version on my laptop. Today I performed a successful installation on my laptop but when I reboot, it doesn't show me the Ubuntu OS in the list (I can only see Windows7). Is there any way to bring up the Ubuntu entry into this list? While installing I selected the option to have both Windows7 and Ubuntu OS on my laptop. The root drive for both OS is C: drive. Hence I split the drive into two (250 GB for Windows7 and 250 GB for Ubuntu). Now I can only see 250GB in my C:\ drive for Windows7. Is the remaining 250GB assigned to Ubuntu or did I lose that 250GB space?? Your answers will be highly appreciated..

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• Dual display setup - only one displayed after logon

  - by oneofthemany

  During boot process my desktop shows both Monitors, but after log I only get one. I'm using Ubuntu 11.10 When I go into Displays its still only shows on Monitor. Here is my graphics card details: 01:00.0 VGA compatible controller: nVidia Corporation G72 [GeForce 7300 LE] (rev a1) (prog-if 00 [VGA controller]) Subsystem: Dell Device 0405 Flags: bus master, fast devsel, latency 0, IRQ 16 Memory at dd000000 (32-bit, non-prefetchable) [size=16M] Memory at c0000000 (64-bit, prefetchable) [size=256M] Memory at de000000 (64-bit, non-prefetchable) [size=16M] [virtual] Expansion ROM at dfe00000 [disabled] [size=128K] Capabilities: <access denied> Kernel driver in use: nvidia Kernel modules: nvidia_96, nvidia_173, nouveau, nvidiafb

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• Connecting 2 PCs using USB-to-USB (male-male) cable

  - by Amirizzuan

  I found this while Googling around: http://www.hardwaresecrets.com/article/Connecting-Two-PCs-Using-a-USB-USB-Cable/248 But then, the solution given in the article is using Windows. Is there any Ubuntu equivalent to this? I would really love to SSH into my Ubuntu server via my Ubuntu laptop, just by connecting one end of the male USB to my laptop, and another end of the male USB to my server. I know I can always SSH into my server via the network, but then in this case of mine, there are cases the server is inside a secluded-secured network server room, and the only way for me to check things out is to go into the server room and open the keyboard console and monitor there. But, if I can just bring my laptop inside and connect to the USB there, then that would be cool. Any idea guys?

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• Implementing a State Machine in Angular.js to control routing

  - by ldn_tech_exec

  Can anyone help me with integrating a state machine to control routing? What's the best method to do this? Create a service? I need to basically intercept every $location request, run the state machine and let it figure out what the next $location.path should be. Think of the problem like a bank of questions that get added and removed over time. The user visits once in a while, passes in the user's answers object to the statemachine, and the statemachine figures out which question to load. This is my pseudocode, but i need to figure out where to put this or what event I can hook into to make sure all route requests are passed through the machine. Do I need a specific stateMachine controller? Do I create a service? Where do I use the service? Do I need to override $locationProvider? $scope.user.answers = [{ id: 32, answer: "whatever" }, { id:33, answer: "another answer" }] $scope.questions = [{ id:32, question:"what is your name?", path:"/question/1" },{ id:34, question:"how old are you?", path:"/question/2" }] var questions = $scope.questions; angular.forEach(questions, function(question) { if(question.id !exist in $scope.user.answers.id) { $location.path = question.path break; }); Thanks

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• BASH: How to count all the human readable files?

  - by user1687406

  I'm taking an intro course to UNIX and have a homework question that follows: How many files in the previous question are text files? A text file is any file containing human-readable content. (TRICK QUESTION. Run the file command on a file to see whether the file is a text file or a binary data file! If you simply count the number of files with the ".txt" extension you will get no points for this question.) The previous question simply asked how many regular files there were, which was easy to figure out by doing find . -type f | wc -l I'm just having trouble determining what "human readable content" is, since I'm assuming it means anything besides binary/assembly, but I thought that's what -type f displays. Maybe that's what the professor meant by saying "trick question"? This question has a follow up later that also asks "What text files contain the string "csc" in any mix of upper and lower case?". Obviously "text" is referring to more than just .txt files, but I need to figure out the first question to determine this!

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• Redirecting users after destroy

  - by mathee

  I have 3 models: Questions, Answers, and Profiles (I know, it should be called "Users"). When you view a question Q, I query the database for the answers to Q. (They are linked by id.) In the view, the current user has the option to delete his answer by clicking on the destroy link displayed next to his answer: %table %tr %td Answers: - @answers.each do |a| %tr %td - @provider = Profile.find(a.provider) %i #{h @provider.username} said: %br #{h a.description} %td = link_to 'View full answer', a %td - if a.provider == @profile.id #{link_to 'Delete my answer', a, :confirm => 'Are you sure?', :method => :delete} The problem is that when the user clicks on the destroy link, it redirects to the /answers/index. I want it to redirect to /questions/Q. What's the best way to do this? I know that there's a redirect_to method, but I don't know how to implement it when I want to redirect to an action for a different controller. It also needs to remember the question from which the answer is being deleted. I tried passing something like :question_id in link_to as: #{link_to 'Delete my answer', a, :confirm => 'Are you sure?', :question_id => @question.id, :method => :delete} In AnswersController#destroy: def destroy @answer = Answer.find(params[:id]) @answer.destroy respond_to do |format| format.html { redirect_to(answers_url) } format.xml { head :ok } end @question = Question.find(params[:question_id]) redirect_to question_path(@question) end The :question_id information is not passed to the destroy method, so I get this error: Couldn't find Question without an ID To confirm, I added a puts call before Question.find, and it returned nil.

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• ROR accepts_nested_attributes_for one to many relationship with selection

  - by bilash.saha

  I have two models Doctors and Questions like the follwong: Doctor Model class Doctor < ActiveRecord::Base has_many :questions has_many :brands accepts_nested_attributes_for :questions end Question model class Question < ActiveRecord::Base belongs_to :discipline belongs_to :doctor belongs_to :brand end Now you can clearly see that Doctor has many questions and brands and question belongs to doctor and brand.I want to add previously saved question to a doctor from doctors edit page. I want to remove them as well.How can I proceed ? I tried like : <%= form.fields_for :questions, question,:child_index => (question.new_record? ? "index_to_replace_with_js" : nil) do |question_form| %> <table> <tr> <td> <div class="label">Select Question</div> <%= question_form.collection_select :id, Question.all, :id, :title ,{:include_blank => true } %> </td> </tr> </table> but this doesnot works for me.Can you give me a solution with proper example ?

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• where is the best palce to count the lazy load property using JPA

  - by Ke

  Let's say we have a "Question" and "Answer" entity, @Entity public class Question extends IdEntity { @Lob private String content; @Transient private int answerTotal; @OneToMany(fetch = FetchType.LAZY) private List<Answer> answers = new ArrayList<Answer>(); ...... I need to tell how many answers for the question every time Question is queryed. So I need to do count: String count = "select count(o) from Answer o WHERE o.question=:q"; My question is, where is the best place to do the count? (Because I did a lot of query about Question entity, by date, by tag, by category, by asker, etc. It is obviously not a good solution to add count operation in each query. My first attempt is to implement a @PostLoad listener, so every time Question entity is loaded, I do count. However, EntityManager cannot be injected in listener. So this way does not work. Any hint?

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• How do i map this in NHibernate

  - by Andrew Smith

  I Have two classes, Survey and Poll classes. Also I have Question and Question Choice classes. How do I map these so I come out with particular table formats. here is the classes involved. public class Survey { public IList<Question> Questions { get; private set; } } public class Poll { public Question Question { get; set; } } public class Question { public string Text { get; set; } public IList<QuestionChocie> Choices { get; private set; } } public class QuestionChoice { public string Text { get; set; } } The resulting tables that I'm shooting for include the following Surveys- a table of survey information. Polls - a table of polls information. SurveyQuestions -a table of survey questions. PollQuestions - a table of poll questions. SurveyChoices - a table of the question choices for the surveys. PollChoices - a table of the question choices for the survey. preferably i really want to know for fluent nhibernate, or just mapping xml is fine too.

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• Looping Through Database Query

  - by DrakeNET

  I am creating a very simple script. The purpose of the script is to pull a question from the database and display all answers associated with that particular question. We are dealing with two tables here and there is a foreign key from the question database to the answer database so answers are associated with questions. Hope that is enough explanation. Here is my code. I was wondering if this is the most efficient way to complete this or is there an easier way? <html> <head> <title>Advise Me</title> <head> <body> <h1>Today's Question</h1> <?php //Establish connection to database require_once('config.php'); require_once('open_connection.php'); //Pull the "active" question from the database $todays_question = mysql_query("SELECT name, question FROM approvedQuestions WHERE status = active") or die(mysql_error()); //Variable to hold $todays_question aQID $questionID = mysql_query("SELECT commentID FROM approvedQuestions WHERE status = active") or die(mysql_error()); //Print today's question echo $todays_question; //Print comments associated with today's question $sql = "SELECT commentID FROM approvedQuestions WHERE status = active"; $result_set = mysql_query($sql); $result_num = mysql_numrows($result_set); for ($a = 0; $a < $result_num; $a++) { echo $sql; } ?> </body> </html>

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• Ordering .each results in the view...

  - by bgadoci

  I am wondering if it is possible to dictate the order (i.e. :order = 'created_at DESC') within the view. I realize that logic in the view is not ideal but I seem to be having some problems locating where to affect this output. For instance, here is my code: <% @user.questions.each do |question| %> <%= link_to_unless_current h (question.title), question %> Created about <%= time_ago_in_words h(question.created_at) %> ago Updated about <%= time_ago_in_words h(question.updated_at) %> ago <%= link_to 'Edit', edit_question_path(question) %> | <%= link_to 'Destroy', question, :confirm => 'Are you sure?', :method => :delete %> <% end %> In my QuestionsController I have the following index action but it is not affecting the output from the code above. class QuestionsController < ApplicationController def index @questions = Question.all(:order => 'created_at DESC', :limit => 20) respond_to do |format| format.html # index.html.erb format.xml { render :xml => @questions } end end end

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• Silverlight ~ MVVM ~ Dynamic setting of Style property based on model value

  - by eponymous23

  I have a class called Question that represents a question and it's answer. I have an application that renders an ObservableCollection of Question objects. Each Question is rendered as a StackPanel that contains a TextBlock for the question verbiage, and a TextBox for the user to enter in an answer. The questions are rendered using an ItemsControl, and I have initially set the Style of the Questions's StackPanel using a StaticResource key called 'IncorrectQuestion' (defined in UserControl.Resources section of the page). In the UserControl.Resources section, I've also defined a key calld 'CorrectQuestion' which I need to somehow apply to the Question's StackPanel when the user correctly answers the question. My problem is I'm not sure how to dynamically change the Style of the StackPanel, specifically within the constraints of a ViewModel class (i.e. I don't want to put any style selection code in the View's code-behind). My Question class has an IsCorrect property which is accurately being set when the correction is answered. I'd like to somehow reflect the IsCorrect value in the form of a Style selection. How do I do that?

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• Answers to Your Common Oracle Database Lifecycle Management Questions

  - by Scott McNeil

  We recently ran a live webcast on Strategies for Managing Oracle Database's Lifecycle. There were tons of questions from our audience that we simply could not get to during the hour long presentation. Below are some of those questions along with their answers. Enjoy! Question: In the webcast the presenter talked about “gold” configuration standards, for those who want to use this technique, could you recommend a best practice to consider or follow? How do I get started? Answer:Gold configuration standardization is a quick and easy way to improve availability through consistency. Start by choosing a reference database and saving the configuration to the Oracle Enterprise Manager repository using the Save Configuration feature. Next create a comparison template using the Oracle provided template as a starting point and modify the ignored properties to eliminate expected differences in your environment. Finally create a comparison specification using the comparison template you created plus your saved gold configuration and schedule it to run on a regular basis. Don’t forget to fill in the email addresses of those you want to notify upon drift detection. Watch the database configuration management demo to learn more. Question: Can Oracle Lifecycle Management Pack for Database help with patching an Oracle Real Application Cluster (RAC) environment? Answer: Yes, Oracle Enterprise Manager supports both parallel and rolling patch application of Oracle Real Application Clusters. The use of rolling patching is recommended as there is no downtime involved. For more details watch this demo. Question: What are some of the things administrators can do to control configuration drift? Why is it important? Answer:Configuration drift is one of the main causes of instability and downtime of applications. Oracle Enterprise Manager makes it easy to manage and control drift using scheduled configuration comparisons combined with comparison templates. Question: Does Oracle Enterprise Manager 12c Release 2 offer an incremental update feature for "gold" images? For instance, if the source binary has a higher PSU level, what is the best approach to update the existing "gold" image in the software library? Do you have to create a new image or can you just update the original one? Answer:Provisioning Profiles (Gold images) can contain the installation files and database configuration templates. Although it is possible to make some changes to the profile after creation (mainly to configuration), it is normally recommended to simply create a new profile after applying a patch to your reference database. Question: The webcast talked about enforcing in-house standards, does Oracle Enterprise Manager 12c offer verification of your databases and systems to those standards? For example, the initial "gold" image has been massively deployed over time, and there may be some changes to it. How can you do regular checks from Enterprise Manager to ensure the in-house standards are being enforced? Answer:There are really two methods to validate conformity to standards. The first method is to use gold standards which you compare other databases to report unwanted differences. This method uses a new comparison template technology which allows users to ignore known differences (i.e. SID, Start time, etc) which results in a report only showing important or non-conformant differences. This method is quick to setup and configure and recommended for those who want to get started validating compliance quickly. The second method leverages the new compliance framework which allows the creation of specific and robust validations. These compliance rules are grouped into standards which can be assigned to databases quickly and easily. Compliance rules allow for targeted and more sophisticated validation beyond the basic equals operation available in the comparison method. The compliance framework can be used to implement just about any internal or industry standard. The compliance results will track current and historic compliance scores at the overall and individual database targets. When the issue is resolved, the score is automatically affected. Compliance framework is the recommended long term solution for validating compliance using Oracle Enterprise Manager 12c. Check out this demo on database compliance to learn more. Question: If you are using the integration between Oracle Enterprise Manager and My Oracle Support in an "offline" mode, how do you know if you have the latest My Oracle Support metadata? Answer:In Oracle Enterprise Manager 12c Release 2, you now only need to download one zip file containing all of the metadata xmls files. There is no indication that the metadata has changed but you could run a checksum on the file and compare it to the previously downloaded version to see if it has changed. Question: What happens if a patch fails while administrators are applying it to a database or system? Answer:A large portion of Oracle Enterprise Manager's patch automation is the pre-requisite checks that happen to ensure the highest level of confidence the patch will successfully apply. It is recommended you test the patch in a non-production environment and save the patch plan as a template once successful so you can create new plans using the saved template. If you are using the recommended ‘out of place’ patching methodology, there is no urgency because the database is still running as the cloned Oracle home is being patched. Users can address the issue and restart the patch procedure at the point it left off. If you are using 'in place' method, you can address the issue and continue where the procedure left off. Question: Can Oracle Enterprise Manager 12c R2 compare configurations between more than one target at the same time? Answer:Oracle Enterprise Manager 12c can compare any number of target configurations at one time. This is the basis of many important use cases including Configuration Drift Management. These comparisons can also be scheduled on a regular basis and emails notification sent should any differences appear. To learn more about configuration search and compare watch this demo. Question: How is data comparison done since changes are taking place in a live production system? Answer:There are many things to keep in mind when using the data comparison feature (as part of the Change Management ability to compare table data). It was primarily intended to be used for maintaining consistency of important but relatively static data. For example, application seed data and application setup configuration. This data does not change often but is critical when testing an application to ensure results are consistent with production. It is not recommended to use data comparison on highly dynamic data like transactional tables or very large tables. Question: Which versions of Oracle Database can be monitored through Oracle Enterprise Manager 12c? Answer:Oracle Database versions: 9.2.0.8, 10.1.0.5, 10.2.0.4, 10.2.0.5, 11.1.0.7, 11.2.0.1, 11.2.0.2, 11.2.0.3. Watch the On-Demand Webcast Stay Connected: Twitter | Facebook | YouTube | Linkedin | NewsletterDownload the Oracle Enterprise Manager Cloud Control12c Mobile app

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• What is Active Directory and how does it work?

  - by MDMarra

  This is a Canonical Question about Active Directory. What is Active Directory? What does it do and how does it work? I find myself explaining some of what I assume is common knowledge about it almost daily. This question will, hopefully, serve as a canonical question and answer for most basic Active Directory questions. If you feel that you can improve the answer to this question, please edit away.

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• My server is slower than the average user's computer, should I still offload Access queries to SQL Server? [closed]

  - by andrewb

  Possible Duplicate: How do you do Load Testing and Capacity Planning for Databases I have a database set up with MS Access 2007 front ends and an SQL Server 2005 back end. At the moment, all the queries are saved in the front end as I've only recently moved to an SQL Server backend. I'm wondering how much of those queries I should save as stored procedures/views on SQL Server. About the system The number of concurrent users is only a handful, though it could be as high as 25 at one time (very unlikely). The average computer has an Intel i3-2120 CPU running at 3.3 GHz, which gets a PassMark score of 3,987, whilst the server has an Intel Xeon E5335 running at 2.0 GHz, which gets a PassMark score of 2,637. Always an awkward situation when an i3 outperforms a Xeon... though the i3 is from Q1 2011 and the Xeon is Q2 2009. There is potential for a server upgrade in the future, though it wouldn't come easy. I'm inclined to move the queries to the back end, as they are beginning to take noticeable time and I figure that is a better way of doing things. I like the idea of throwing everything at the server, then pushing for a server upgrade. It makes more sense in my mind to be upgrading one server rather than 30 PCs. Or am I being overzealous? Why my question isn't a duplicate It seems that my question has been misinterpreted and labelled a duplicate of quite a different question, one about testing and capacity planning. I'll try explain how my question is very different from the linked question. The crux of my question is something like "Even though my server is technically slower, is it better to have it doing more of the queries?" There's two ways that people could have answered this: I agree the server is going to be slower, but the extra benefits of such and such (like the less Access the better) means you should move most to the server anyway. (OR no it doesn't outweigh the benefit, keep them in Access) Actually the server will be faster because of such and such. I'm hoping that people out there could provide some answers like this, and the question in the dupe link doesn't really provide either of these answers. Ok sure, I suppose I could do extensive performance testing to compare Access queries running on a local machine to SQL Server queries running on the server, but that sounds like a very hard task (particularly performance testing of access) compared to someone giving some quick general guidance, and again, my question is looking for a lot more than immediate performance benefit.

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• Issues printing through ssh tunnel and port forwarding

  - by simogasp

  I'm having some problems trying to print through a ssh tunnel. I'd like to print from my laptop to a network printer (Toshiba es453, for what matters) which is in a local network. I can reach the local network using a gateway. So far I did the following: ssh -N -L19100:<Printer_IP>:9100 <username>@<ssh_gateway> Basically i just mapped the port 19100 of my laptop directly to the input port of the printer, passing through the gateway. So far, so good. Then, i tried to install on my laptop a new printer with the GUI config tool of ubuntu, so that the new printer is on localhost at port 19100 (as APP Socket/HP Jet Direct) , then I provided the proper driver of the printer. In theory, once the tunnel is open I should be able to print from any program just selecting this printer. Of course, it does not work. :-) The document hangs in the queue with status Processing while in the shell where I set up the tunnel I get these errors on failing opening channels debug1: Local forwarding listening on ::1 port 19100. debug1: channel 0: new [port listener] debug1: Local forwarding listening on 127.0.0.1 port 19100. debug1: channel 1: new [port listener] debug1: Requesting [email protected] debug1: Entering interactive session. debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 3: new [direct-tcpip] channel 2: open failed: connect failed: Connection timed out debug1: channel 2: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44434, nchannels 4 debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] channel 3: open failed: connect failed: Connection timed out debug1: channel 3: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44443, nchannels 4 channel 2: open failed: connect failed: Connection timed out debug1: channel 2: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44493, nchannels 3 debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] As a further debugging test I tried the following. From a machine inside the local network I did a telnet <IP_printer> 9100, got access, wrote some random thing, closed the connection and correctly I got a print of what I had written. So the port and the ip of the printer should be correct. I tried the same from my laptop with the tunnel opened, the telnet succeeded but, again, the printer didn't print anything, getting the usual channel x: open failed: errors. I'm not a great expert on the matter, I just thought that in theory it was possible to do something like that, but maybe there is something that I didn't consider or I did wrong. Any clue? Thanks! Simone [update] As further debugging test, I tried to replicate the procedure from a machine in the local network. From that machine, I did ssh -N -L19100:<IP_printer>:9100 <username>@<ssh_gateway> (note that now the machine, the gateway and the printer are in the same local network) then I tried again the telnet test with telnet localhost 19100, I got access and everything, but I didn't get the print but the usual error channel 2: open failed: connect failed: Connection timed out Maybe I am missing some other connection to be forwarded or maybe this is not allowed by the administrators. Of course, if I connect via ssh tunneling to the local machine from my laptop through the gateway, I can successfully print using the lpr command (from the local machine). But this is what I would like to avoid (yes, I'm lazy...:-), I would like to have a more 'elegant' and transparent way to do that.

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• Why would Copying a Large Image to the Clipboard Freeze a Computer?

  - by Akemi Iwaya

  Sometimes, something really odd happens when using our computers that makes no sense at all…such as copying a simple image to the clipboard and the computer freezing up because of it. An image is an image, right? Today’s SuperUser post has the answer to a puzzled reader’s dilemna. Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. Original image courtesy of Wikimedia. The Question SuperUser reader Joban Dhillon wants to know why copying an image to the clipboard on his computer freezes it up: I was messing around with some height map images and found this one: (http://upload.wikimedia.org/wikipedia/commons/1/15/Srtm_ramp2.world.21600×10800.jpg) The image is 21,600*10,800 pixels in size. When I right click and select “Copy Image” in my browser (I am using Google Chrome), it slows down my computer until it freezes. After that I must restart. I am curious about why this happens. I presume it is the size of the image, although it is only about 6 MB when saved to my computer. I am also using Windows 8.1 Why would a simple image freeze Joban’s computer up after copying it to the clipboard? The Answer SuperUser contributor Mokubai has the answer for us: “Copy Image” is copying the raw image data, rather than the image file itself, to your clipboard. The raw image data will be 21,600 x 10,800 x 3 (24 bit image) = 699,840,000 bytes of data. That is approximately 700 MB of data your browser is trying to copy to the clipboard. JPEG compresses the raw data using a lossy algorithm and can get pretty good compression. Hence the compressed file is only 6 MB. The reason it makes your computer slow is that it is probably filling your memory up with at least the 700 MB of image data that your browser is using to show you the image, another 700 MB (along with whatever overhead the clipboard incurs) to store it on the clipboard, and a not insignificant amount of processing power to convert the image into a format that can be stored on the clipboard. Chances are that if you have less than 4 GB of physical RAM, then those copies of the image data are forcing your computer to page memory out to the swap file in an attempt to fulfil both memory demands at the same time. This will cause programs and disk access to be sluggish as they use the disk and try to use the data that may have just been paged out. In short: Do not use the clipboard for huge images unless you have a lot of memory and a bit of time to spare. Like pretty graphs? This is what happens when I load that image in Google Chrome, then copy it to the clipboard on my machine with 12 GB of RAM: It starts off at the lower point using 2.8 GB of RAM, loading the image punches it up to 3.6 GB (approximately the 700 MB), then copying it to the clipboard spikes way up there at 6.3 GB of RAM before settling back down at the 4.5-ish you would expect to see for a program and two copies of a rather large image. That is a whopping 3.7 GB of image data being worked on at the peak, which is probably the initial image, a reserved quantity for the clipboard, and perhaps a couple of conversion buffers. That is enough to bring any machine with less than 8 GB of RAM to its knees. Strangely, doing the same thing in Firefox just copies the image file rather than the image data (without the scary memory surge). Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

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• Best Practices - Core allocation

  - by jsavit

  This post is one of a series of "best practices" notes for Oracle VM Server for SPARC (also called Logical Domains) Introduction SPARC T-series servers currently have up to 4 CPU sockets, each of which has up to 8 or (on SPARC T3) 16 CPU cores, while each CPU core has 8 threads, for a maximum of 512 dispatchable CPUs. The defining feature of Oracle VM Server for SPARC is that each domain is assigned CPU threads or cores for its exclusive use. This avoids the overhead of software-based time-slicing and emulation (or binary rewriting) of system state-changing privileged instructions used in traditional hypervisors. To create a domain, administrators specify either the number of CPU threads or cores that the domain will own, as well as its memory and I/O resources. When CPU resources are assigned at the individual thread level, the logical domains constraint manager attempts to assign threads from the same cores to a domain, and avoid "split core" situations where the same CPU core is used by multiple domains. Sometimes this is unavoidable, especially when domains are allocated and deallocated CPUs in small increments. Why split cores can matter Split core allocations can silenty reduce performance because multiple domains with different address spaces and memory contents are sharing the core's Level 1 cache (L1$). This is called false cache sharing since even identical memory addresses from different domains must point to different locations in RAM. The effect of this is increased contention for the cache, and higher memory latency for each domain using that core. The degree of performance impact can be widely variable. For applications with very small memory working sets, and with I/O bound or low-CPU utilization workloads, it may not matter at all: all machines wait for work at the same speed. If the domains have substantial workloads, or are critical to performance then this can have an important impact: This blog entry was inspired by a customer issue in which one CPU core was split among 3 domains, one of which was the control and service domain. The reported problem was increased I/O latency in guest domains, but the root cause might be higher latency servicing the I/O requests due to the control domain being slowed down. What to do about it Split core situations are easily avoided. In most cases the logical domain constraint manager will avoid it without any administrative action, but it can be entirely prevented by doing one of the several actions: Assign virtual CPUs in multiples of 8 - the number of threads per core. For example: ldm set-vcpu 8 mydomain or ldm add-vcpu 24 mydomain. Each domain will then be allocated on a core boundary. Use the whole core constraint when assigning CPU resources. This allocates CPUs in increments of entire cores instead of virtual CPU threads. The equivalent of the above commands would be ldm set-core 1 mydomain or ldm add-core 3 mydomain. Older syntax does the same thing by adding the -c flag to the add-vcpu, rm-vcpu and set-vcpu commands, but the new syntax is recommended. When whole core allocation is used an attempt to add cores to a domain fails if there aren't enough completely empty cores to satisfy the request. See https://blogs.oracle.com/sharakan/entry/oracle_vm_server_for_sparc4 for an excellent article on this topic by Eric Sharakan. Don't obsess: - if the workloads have minimal CPU requirements and don't need anywhere near a full CPU core, then don't worry about it. If you have low utilization workloads being consolidated from older machines onto a current T-series, then there's no need to worry about this or to assign an entire core to domains that will never use that much capacity. In any case, make sure the most important domains have their own CPU cores, in particular the control domain and any I/O or service domain, and of course any important guests. Summary Split core CPU allocation to domains can potentially have an impact on performance, but the logical domains manager tends to prevent this situation, and it can be completely and simply avoided by allocating virtual CPUs on core boundaries.

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• Slow draw on some apps and dynamic clocks not working properly with ATI/AMD proprietary drivers

  - by Rakeka

  I've recently purchased a new computer (around July 2010) and I've been having some problems with proprietary video drivers on Linux. The hardware is: Video: ATI/AMD Radeon HD 5870 (XFX HD-587X-ZNFC); Motherboard: Asus P7P55D-E Deluxe; Processor: Intel i5 750; Memory: Kingston Hyperx KHX1600C8D3K2/4GX (2x - 8GB Total); Power Supply: XFX P1-750B-CAG9; There are no overclocks, not even the memories (they are at 1333mhz due processor memory controller limitation). The operational system is a homebrew Linux distribution with the following software: Architecture: x86_64 (multilib) Kernel: 2.6.35.10 Xorg: 7.5 Window Manager: wmii-3.9.2 Video Driver: ATI/AMD Catalyst 10.12 There are no desktop effects programs like compiz fusion or beryl. The problems: With ATI/AMD proprietary driver, some applications are with slow draw/redraw, and, the same applications make the driver to increase the card clocks to maximum (0% gpu activity, only the clocks are increased). I dunno exactly how to describe the slow draw but I'll list some applications and symptoms. xterm Flickers a lot when drawing continuous output; When I'm in a workspace with fullscreen xterm, The gpu load stays at 12% in idle, and, with smaller xterm, smaller GPU load. "aticonfig --odgc" output: Default Adapter - ATI Radeon HD 5800 Series Core (MHz) Memory (MHz) Current Clocks : 157 300 Current Peak : 850 1200 Configurable Peak Range : [600-900] [900-1300] GPU load : 12% "aticonfig --pplib-cmd 'get activity'" output: Current Activity is Core Clock: 157MHZ Memory Clock: 300MHZ VDDC: 950 Activity: 12 percent Performance Level: 0 Bus Speed: 5000 Bus Lanes: 16 Maximum Bus Lanes: 16 More examples: mplayer time info flickers on terminal; "find /" flickers a lot (It takes some time to stop with control-c. But, If I change the workspace or put some window upon it, just after the control-c, it stops instantly); "cat somefile" if the file is big (Xorg.0.log for example) it takes some time to display; vim and less (ex: find / | less) don't have much problems, just a little flicker when scrolling; mplayer (no gui) Slow reproduction and seek with -vo x11; Tearing with -vo xv; Time info flickers on terminal (xterm consequence); gvim A little slow draw when scrolling with page up/page down; Firefox Slow draw/redraw on some pages like www.boadica.com.br and sometimes on www.youtube.com with flash enable (never noticed on many pages); Corruptions when informative yellow boxes are showing and scroll the page (an gray box appears at the same place of the informative box); "Wallpaper" After minimizing a fullscreen window or changing to an empty workspace it takes some time to redraw wallpaper. "Video Card" The core and memory clocks are increased with the events described above and on other situations like change workspace (even without wallpaper), minimize, maximize or move a window; Idle clocks: Core: 157mhz, Memory: 300mhz Full clocks: Core: 850mhz, Memory: 1200mhz xpdf Painful slow scrolling; display (from ImageMagick) Slow menus and sometimes slow image redraw; Programs that I use and are apparently without problems: gimp; pidgin; mplayer (-vo gl, gl2); blender; unigine heaven (better fps than on Windows); doom3; tibia; penumbra overture; amnesia the dark descent (wine); diablo 2 (wine); No problems on Windows (Windows 7 Ultimate 64bit). And special note to this: Full desktop effects from Debian and Ubuntu gnome appearance cpanel don't cause ANY problems, even the core and memory clocks don't increase when change workspace, minimize, maximize or move a window. What I've tested: Unsuccessful tests: Tested all drivers versions since 10.6 (released approximately when I've installed the first slackware in this PC); Tested other video card - ATI/AMD Radeon HD 5570 (XFX HD-557X-ZHF2); Tested some options on xorg.conf and that I've found googling (some of these options are commented on my xorg.conf. I'll send the links at the end of post); Tested some patches like 107_fedora_dont_fill_bg_none.patch and xserver-xorg-backclear.patch from Arch Linux Catalyst page (https://wiki.archlinux.org/index.php/ATI_Catalyst); Tested other distros and software versions: Tested XORG-7.6 on my own distribution; Tested Debian Squeeze (testing - from 2010-12-20); Tested Ubuntu Marverick (10.10); Tested Slackware 13.1; Distros info: Architecture: i386 Debian and Ubuntu with all default software (kernel, gnome, xorg, drivers); Slackware with Catalyst from AMD page and default window managers like: fvwm, xfce, and my own build of wmii; Successful tests: Tested other video card (only on my homebrew distro) - NVIDIA Geforce 7300GS with driver 260.19.29; That didn't shown the slow draw problems, but that card is a bit obsolete, so, dunno if that lacks features like the dynamic clocks. I don't dispose of other video cards like nvidia g/gt/gts/gtx 200~400~500 or Radeon HD 3000/4000/6000 to make more tests. Tested other hardware: Video: ATI/AMD Radeon HD 5570 (XFX HD-557X-ZHF2); Motherboard: Intel DG31PR; Processor: Core 2 Duo E6750; Software for that hardware: Fresh install of same distros (except for the mine) with same program versions; That video card (HD 5570) were full time at the maximum clocks (something like 500/750, don't remember) in all the operational systems (Windows XP and Windows 7 too), but it didn't shown the same problems that I have here. I've googled a lot about common problems with ATI/AMD proprietary drivers for Linux and didn't find similar problems, except by the Firefox corruptions, that the solutions were to disable ATI Direct2DAccel and use XAA. With XAA the problems persists and the other applications like pidgin and rest of Firefox showed the same problems of slow draw/redraw. Open source Drivers: With open source drivers (xf86-video-ati-6.13.2) I hadn't the same slow draw problems, but, had other problems, that, for now, make it no viable solution. I'll not discuss it here because this is another line of problems and will confuse everything. If it happens to be the only solution, I'll make another thread to discuss it. Logs and Configs: kernel .config dmesg xorg package list xorg.conf Xorg.0.log

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 6

  - by MarkPearl

  Learning Outcomes Discuss the physical characteristics of magnetic disks Describe how data is organized and accessed on a magnetic disk Discuss the parameters that play a role in the performance of magnetic disks Describe different optical memory devices Magnetic Disk The way data is stored on and retried from magnetic disks Data is recorded on and later retrieved form the disk via a conducting coil named the head (in many systems there are two heads) The writ mechanism exploits the fact that electricity flowing through a coil produces a magnetic field. Electric pulses are sent to the write head, and the resulting magnetic patterns are recorded on the surface below with different patterns for positive and negative currents The physical characteristics of a magnetic disk   Summarize from book   The factors that play a role in the performance of a disk Seek time – the time it takes to position the head at the track Rotational delay / latency – the time it takes for the beginning of the sector to reach the head Access time – the sum of the seek time and rotational delay Transfer time – the time it takes to transfer data RAID The rate of improvement in secondary storage performance has been considerably less than the rate for processors and main memory. Thus secondary storage has become a bit of a bottleneck. RAID works on the concept that if one disk can be pushed so far, additional gains in performance are to be had by using multiple parallel components. Points to note about RAID… RAID is a set of physical disk drives viewed by the operating system as a single logical drive Data is distributed across the physical drives of an array in a scheme known as striping Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure (not supported by RAID 0 or RAID 1) Interesting to note that the increase in the number of drives, increases the probability of failure. To compensate for this decreased reliability RAID makes use of stored parity information that enables the recovery of data lost due to a disk failure.   The RAID scheme consists of 7 levels…   Category Level Description Disks Required Data Availability Large I/O Data Transfer Capacity Small I/O Request Rate Striping 0 Non Redundant N Lower than single disk Very high Very high for both read and write Mirroring 1 Mirrored 2N Higher than RAID 2 – 5 but lower than RAID 6 Higher than single disk Up to twice that of a signle disk for read Parallel Access 2 Redundant via Hamming Code N + m Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Parallel Access 3 Bit interleaved parity N + 1 Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Independent Access 4 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, significantly lower than single disk for write Similar to RAID 0 for read, significantly lower than single disk for write Independent Access 5 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, lower than single disk for write Similar to RAID 0 for read, generally  lower than single disk for write Independent Access 6 Block interleaved parity N + 2 Highest of all listed alternatives Similar to RAID 0 for read; lower than RAID 5 for write Similar to RAID 0 for read, significantly lower than RAID 5  for write   Read page 215 – 221 for detailed explanation on RAID levels Optical Memory There are a variety of optical-disk systems available. Read through the table on page 222 – 223 Some of the devices include… CD CD-ROM CD-R CD-RW DVD DVD-R DVD-RW Blue-Ray DVD Magnetic Tape Most modern systems use serial recording – data is lade out as a sequence of bits along each track. The typical recording used in serial is referred to as serpentine recording. In this technique when data is being recorded, the first set of bits is recorded along the whole length of the tape. When the end of the tape is reached the heads are repostioned to record a new track, and the tape is again recorded on its whole length, this time in the opposite direction. That process continued back and forth until the tape is full. To increase speed, the read-write head is capable of reading and writing a number of adjacent tracks simultaneously. Data is still recorded serially along individual tracks, but blocks in sequence are stored on adjacent tracks as suggested. A tape drive is a sequential access device. Magnetic tape was the first kind of secondary memory. It is still widely used as the lowest-cost, slowest speed member of the memory hierarchy.

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