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• SSH attcack CentOS Amazon EC2

  - by user37143

  Hi, I run a few Rightscale CentOS AMI based instances on Amazon EC2. Two months back I found that our SSHD security is compromised( I had added host.allow and host.deny for ssh). So I created new instances and done an IP based ssh that allows only our IPs through AWS Firewall(ec2-authorize) and chnaged the ssh 22 default port to some other port but two days back I found I was not able to login to the server and when I tried on 22 port the ssh got connected and I found that sshd_conf was changed and when I tried to edit sshd_config I found root had no write permission on the file. So I tried a chmod and it said access denied for 'root' user. This is very strange. I checked secure log and history and found nothing informative. I have PHP, Ruby On Rails, Java, Wordpress apps running on these server. This time I did a chkrootkit scan and found nothing. I renamed the /etc/ssh folder and reinstalled openssh through yum. I had faced this on 3 instances on CentOS(5.2, 5.4) I have instances on Debian as well those working fine. Is this a CentOS/Rightscale issue. Guys, what security measures I should take to prevent this. Please support me this is very critical. Thanks

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• Loadbalancing with nginx and tomcat

  - by London

  Hello this should be fairly easy to answer for any system admin, the problem is that I'm not server admin but I have to complete this task, I'm very close but still not managing to do it. Here is what I mean, I have two tomcat instance running on machine1 and machine2. People usually access those by visiting urls : http://machine1:8080/appName http://machine2:9090/appName The problem is when I setup nginx with domain name i.e domain.com, nginx sends requests to http://machine1:8080/ and http://machine2:9090/ instead of http://machine1:8080/ and http://machine2:9090/appName Here is my configuration (very basic as it can be noted) : upstream backend { server machine1:8080; server machine2:9090; } server { listen 80; server_name www.mydomain.com mydomain.com; location / { # needed to forward user's IP address to rails proxy_set_header X-Real-IP $remote_addr; # needed for HTTPS proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header Host $http_host; proxy_redirect off; proxy_max_temp_file_size 0; proxy_pass http://backend; } #end location } #end server What changes must I do to do the following : - when user visits mydomain.com - transfer him to either machine1:8080/appName or machine2:9090 Thank you

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• passenger and apache memory usage

  - by Brent Faulkner

  On a "CentOS release 6.2 (Final)" server (with Ruby 1.9.3 and Rails 3.2), and using more memory than expected. Looking at passenger-memory-stats I see a couple of HUGE httpd processes... any thoughts on how I can figure out what's going on and reduce the memory usage? Stats are included here... thanks! ---------- Apache processes ----------- PID PPID VMSize Private Name --------------------------------------- 1371 1 202.1 MB 0.1 MB /usr/sbin/httpd 4573 1371 210.2 MB 5.0 MB /usr/sbin/httpd 4778 1371 202.5 MB 0.6 MB /usr/sbin/httpd 4780 1371 217.6 MB 9.4 MB /usr/sbin/httpd 4781 1371 217.1 MB 9.1 MB /usr/sbin/httpd 4856 1371 202.4 MB 0.5 MB /usr/sbin/httpd 4863 1371 204.1 MB 2.1 MB /usr/sbin/httpd 5027 1371 202.4 MB 0.5 MB /usr/sbin/httpd 5043 1371 202.4 MB 0.4 MB /usr/sbin/httpd 5044 1371 205.5 MB 2.7 MB /usr/sbin/httpd 5072 1371 202.4 MB 0.5 MB /usr/sbin/httpd 5084 1371 202.4 MB 0.5 MB /usr/sbin/httpd 32111 1371 1297.0 MB 246.5 MB /usr/sbin/httpd 32579 1371 1914.3 MB 215.5 MB /usr/sbin/httpd ### Processes: 14 ### Total private dirty RSS: 493.42 MB -------- Nginx processes -------- ### Processes: 0 ### Total private dirty RSS: 0.00 MB ----- Passenger processes ----- PID VMSize Private Name ------------------------------- 4180 280.5 MB 24.4 MB Passenger ApplicationSpawner: /var/www/apps/people/current 4345 309.5 MB 53.4 MB Rack: /var/www/apps/people/current 4800 300.2 MB 55.2 MB Rack: /var/www/apps/people/current 4808 297.8 MB 52.5 MB Rack: /var/www/apps/people/current 4815 297.4 MB 52.4 MB Rack: /var/www/apps/people/current 4822 302.7 MB 55.6 MB Rack: /var/www/apps/people/current 22780 209.0 MB 0.0 MB PassengerWatchdog 22783 991.5 MB 1.3 MB PassengerHelperAgent 22785 113.4 MB 1.1 MB Passenger spawn server 22788 144.6 MB 0.0 MB PassengerLoggingAgent 22911 310.4 MB 64.0 MB Rack: /var/www/apps/people/current 22939 311.6 MB 53.5 MB Rack: /var/www/apps/people/current 26175 304.1 MB 55.8 MB Rack: /var/www/apps/people/current 26182 310.4 MB 44.0 MB Rack: /var/www/apps/people/current ### Processes: 14 ### Total private dirty RSS: 513.24 MB

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• How to track things that SHOULD happen, but might not have

  - by Kamiel Wanrooij

  I am running into a couple of issues with some applications we've deployed and maintain. I have the feeling we have approached this with some anti-patterns up to now, but I would like to see how to make this more flexible and stable. In one situation, we have a server at a client which pushes data to us to parse every night (yes, Windows Task Scheduler). This is highly unstable however, so once every month this doesn't happen because of reasons out of our control. This heavily impacts our business since we run with stale data in that situation. In another scenario we have a lot of background job processes that should be running. We already keep them up using bluepill ( http://www.github.com/arya/bluepill ) but obviously restarts happen, both automatically and manually, and people forget things or systems mess up. What I would like to track is events that should occur or should be available. Like the existence of a process, the execution of a program, or the creation/age of a file, and track it when they don't happen or exist. We develop most things in Ruby on Rails, use NewRelic, Bluepill and Munin, and run on Ubuntu. I've been toying around with counting ps aux | grep processname | wc -l in Munin scripts, or capturing the age of a file and raising alerts over 24-26 hours, stuff like that. Is there better tooling to track things that should happen, and raise alerts if they don't? P.S. I know some things are suboptimal, like manually having to define bluepill for applications and then forgetting to do so. The same goes for the push based approach of the first application, a dedicated daemon that manages that on the client side that we control and can track its connection to us might be a much better solution.

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• Mysterious swap usage on EC2

  - by rusty

  We're in the middle of a project to move our infrastructure from a co-lo situation into Amazon EC2 and we've noticed some weird memory characteristics of the processes in our setup. Without going into too much detail about the specifics of our processes, we've noticed that on our EC2 instances "top" will show processes using a lot of swap space -- in fact, much greater than the amount of available swap or (if you add it all up) more than the available disk. Here's a sample top output: Mem: 7136868k total, 5272300k used, 1864568k free, 256876k buffers Swap: 1048572k total, 0k used, 1048572k free, 2526504k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ SWAP COMMAND 4121 jboss 20 0 5913m 603m 14m S 0.7 8.7 3:59.90 5.2g java 22730 root 20 0 2394m 4012 1976 S 2.0 0.1 4:20.57 2.3g PassengerHelper 20564 rails 20 0 2539m 220m 9828 S 0.3 3.2 0:23.58 2.3g java 1423 nscd 20 0 877m 1464 972 S 0.0 0.0 0:03.89 876m nscd You can see, for instance, that jboss is reportedly using 5.2 gigs of swap space which is definitely impossible since there's only 1G allocated and none is being used (probably because there's still 1.8G of RAM free). And here's the results of uname -a: Linux xxx.yyy.zzz 2.6.35.14-106.53.amzn1.x86_64 #1 SMP Fri Jan 6 16:20:10 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux We're running an AMI based off of the default Amazon Linux AMI (Amazon Linux AMI release 2011.09, so some RHEL5 and RHEL 6) with not too many customizations and definitely no kernel-level customizations. Something here tells me that on this particular kernel/distribution, the reporting of swap or maybe even total memory usage isn't what it appears to be... Any help would be appreciated!

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• apache/httpd responds slower under EL6.1 than EL5.6 (centos)

  - by daniel

  I've read through other threads on performance differences between RHEL6 and RHEL5, but none seem a tight match to mine. My issue manifests itself in slightly slower average response time (20ms) per request. I have about 10/10 servers of the same hardware spec with Cent6.1 and Cent5.6. The issue is consistent across the group. I am running Ruby on Rails with Passenger. Apache config is identical (checked out from the same SVN repo) Ruby and Passenger are identical builds. Application is identical and being served traffic round robin. mod_worker An interesting clue from server-status: The Cent6.1 servers have a steady 20-40 threads in the "Reading Request" state while the Cent5.6 servers have around 1. I'm graphing this so I can see it trend over time. I also have a bunch of much newer machines that are significantly faster and are running Cent6.1. They dust all the older machines in response time, but I can see they also have a steady 20-40 threads in the "Reading Request" state. This makes me believe I can get their response time down, if I can figure out what is holding up these requests. My gut is telling me that I need to tune some network setting in sysctl, but I haven't figured it out yet. Help is appreciated.

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• How to set up a server without a hosting control panel

  - by A4J

  I have always used a control panel on my dedicated servers - from cPanel to Plesk to Virtualmin, and I am now considering ditching a CP altogether and manually editing config files. My requirements are fairly simple, I will host multiple sites on the server; some Apache with PHP & Mysql and some Passenger with Rails & Postgres. All will require email smtp/pop. FTP/Stats will not be required. Could someone please give me a quick run-down of what I would need to do - in terms of installing software and configuration? My server will come with a base install of CentOS 6.4 minimal. My thoughts so far: Install/update latest versions of MySQL & Postgres (are they 'safe' out of the box? Or do I need to do anything else like set up root passwords etc?) Install Apache & PHP (again, are the base installs good to go or do they require security tweaks?) Set up nameservers/hostnames/reverse DNS etc (Any guides on how to do this please?) Install Rubygems Install and configure Dovecot and Postfix (any tips on doing this? Or links to how-tos that cover it please?) Set up each website - any links to guides on how to do this? Install/configure firewall (or is the default install good to go?) Any other tips or advice would be greatly appreciated, as would links to guides or how-tos.

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• solution for an offline server

  - by dashmug

  I'm trying to setup a development server at work that will ideally be able to test drive a couple of projects in PHP, Rails, or Django (not always running at the same time). I develop the apps locally on a Mac and then I'll put the projects up on this server for testing with my actual users (non-techies) before deploying to a production server. My problem is that we have a very poor internet connection (almost negligible) at work and doing the usual apt-get/yum/ports (make, clean, install) processes for setting up servers always get their packages from online repositories somewhere. I know I could probably download the source and then compile them myself but that's going to be too much of a hassle for me. I'm thinking about two solutions: Plan A: Run a server VM on my Mac and then use this VM as the source repository for the offline server. I've read about Ubuntu's apt-proxy and it seems to be good enough though I haven't tried it yet. I'm not sure if this is possible but can I simply do apt-get install nginx --downloadonly so that the package and its dependencies will be downloaded into my VM and my server can use the VM as the source repo for apt-get? Plan B: Run a server VM on my Mac (which I can setup/update easily when I'm home) and then clone the VM to the offline development server. Maybe I should simply make the server a VM host so I can simply copy the VM over. I think this is okay for the first-time setup but subsequent updates will take too long (cloning the VM image). If I was working on Windows, I imagine it'd be easier because most services have an installer file that I can download and then run at the server. If you could suggest another way, it would be much appreciated. Update: From Michael Hampton's answer, I found a possible solution which is apt-cacher. I also found this page on Ubuntu's website. I wonder if there is a better tool than this one.

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• What are the right questions to ask when deciding whether to use Chef or Puppet?

  - by John Feminella

  I am about to start a new project which will, in part, require deploying many identical nodes of approximately three different classes: Data nodes, which will run sharded instances of MongoDB. Application nodes, which will run instances of a Ruby on Rails application and an older ASP.NET MVC application. Processing nodes, which will run jobs requested by the application nodes. ALl the nodes will run on instances of Ubuntu 10.04, though they will have different packages installed. I have some familiarity with Chef from previous projects, though I don't consider myself an expert. In an effort to do due diligence, I have been investigating alternative possibilities. We have a number of folks in-house who are long-time Puppet users, and they have encouraged me to take a look. I am having trouble evaluating both choices, though. Chef and Puppet share many of the same domain terminology -- packages, resources, attributes, and so on, and they have a common history that stems from taking different approaches to the same problem. So in some sense they are very similar. But much of the comparison information I've found, like this article, is a little outdated. If you were starting this project today, what questions would you ask yourself to decide whether you should use Chef or Puppet for configuration management? (Note: I don't want answer to the question "Should I use Chef or Puppet?")

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• Using Monit to monitor Resque

  - by Alex

  I'm trying to use resque as a job runner for Rails. I've tried this config, and many other ways of demonizing the rescue task (because running rake resque:work leaves the terminal tied to that command). Unfortunately, their example configuration doesn't work for me. Does the configuration look correct? Or is there another way to turn the process into a daemon? Thank you :) check process resque_worker_QUEUE with pidfile /data/APP_NAME/current/tmp/pids/resque_worker_QUEUE.pid start program = "/bin/sh -c 'cd /data/APP_NAME/current; RAILS_ENV=production QUEUE=queue_name VERBOSE=1 nohup rake environment resque:work& > log/resque_worker_QUEUE.log && echo $! > tmp/pids/resque_worker_QUEUE.pid'" as uid deploy and gid deploy stop program = "/bin/sh -c 'cd /data/APP_NAME/current && kill -s QUIT `cat tmp/pids/resque_worker_QUEUE.pid` && rm -f tmp/pids/resque_worker_QUEUE.pid; exit 0;'" if totalmem is greater than 300 MB for 10 cycles then restart # eating up memory?

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• Strategy to isolate multiple nginx ssl apps with single domain via suburi's?

  - by icpu

  Warning: so far I have only learnt how to use nginx to serve apps with their own domain and server block. But I think its time to dive a little deeper. To mitigate the need for multiple SSL certificates or expensive wildcard certificates I would like to serve multiple apps (e.g. rails apps, php apps, node.js apps) from one nginx server_name. e.g. rooturl/railsapp rooturl/nodejsapp rooturl/phpshop rooturl/phpblog I am unsure on ideal strategy. Some examples I have seen and or thought about: Multiple location rules, this seems to cause conflicts between the individual app config requirements, e.g. differing rewrite and access requirements Isolated apps by backend internal port, is this possible? Each port routing to its own config? So config is isolated and can be bespoke to app requirements. Reverse proxy, I am little ignorant of how this works, is this what I need to research? is this actually 2 above? Help online seems to always proxy to another server e.g apache What is an effective way to isolate config requirements for apps served from a single domain via sub uris?

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• CNAME vs A records

  - by deb

  I built a small rails app that allow users to make a simple site. It uses subdomain accounts ex: deb.myapp.com Whenever an user wanted to have a domain name associated with their site, they would change their NS records to point to slicehost where the application is hosted and I would manage the DNS records myself. However, as more people are using the application this is not an option for me anymore. I prefer users to keep their nameservers at goddady, register.com, etc, so they can log in and manage their own MX records or whatever else they need to change. My question is, should I have them change the A records to point to my server's ip, or should I have them create a CNAME record? Do they need to delete the default A records to allow the CNAME record to work? Will the A record take precedence and overrule the CNAME record? Thanks in advance. Sorry if this is a very basic question. I've read other posts and I can't find a definite answer.

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• Why do I get "Invalid Column Name" errors in EF4?

  - by camainc

  I am trying to learn Entity Framework 4.0. Disclaimer 1: I am brand new to Entity Framework. I have successfully used LinqToSQL. Disclaimer 2: I am really a VB.Net programmer, so the problem could be in the C# code. Given this code snippet: public int Login(string UserName, string Password) { return _dbContext.Memberships .Where(membership => membership.UserName.ToLower() == UserName.ToLower() && membership.Password == Password) .SingleOrDefault().PrimaryKey; } Why do you suppose I get "Invalid column name" errors? {"Invalid column name 'UserName'.\r\nInvalid column name 'Password'.\r\nInvalid column name 'UserName'.\r\nInvalid column name 'Password'."} Those column names are spelled and cased correctly. I also checked the generated code for the entity in question, and those columns are properties in the entity. The intellisense and code completion also puts the column names into the expression just as they are here. I am stumped by this. Any help would be much appreciated. https://docs.google.com/leaf?id=0B-xLbzoqGvXvNjBmZmNjNDAtY2RhNC00NDA2LWIxNzMtYjhjNTYxMDIyZmZl&hl=en

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• faster implementation of sum ( for Codility test )

  - by Oscar Reyes

  How can the following simple implementation of sum be faster? private long sum( int [] a, int begin, int end ) { if( a == null ) { return 0; } long r = 0; for( int i = begin ; i < end ; i++ ) { r+= a[i]; } return r; } EDIT Background is in order. Reading latest entry on coding horror, I came to this site: http://codility.com which has this interesting programming test. Anyway, I got 60 out of 100 in my submission, and basically ( I think ) is because this implementation of sum, because those parts where I failed are the performance parts. I'm getting TIME_OUT_ERROR's So, I was wondering if an optimization in the algorithm is possible. So, no built in functions or assembly would be allowed. This my be done in C, C++, C#, Java or pretty much in any other. EDIT As usual, mmyers was right. I did profile the code and I saw most of the time was spent on that function, but I didn't understand why. So what I did was to throw away my implementation and start with a new one. This time I've got an optimal solution [ according to San Jacinto O(n) -see comments to MSN below - ] This time I've got 81% on Codility which I think is good enough. The problem is that I didn't take the 30 mins. but around 2 hrs. but I guess that leaves me still as a good programmer, for I could work on the problem until I found an optimal solution: Here's my result. I never understood what is those "combinations of..." nor how to test "extreme_first"

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• python unhashable type - posting xml data

  - by eterry28

  First, I'm not a python programmer. I'm an old C dog that's learned new Java and PHP tricks, but python looks like a pretty cool language. I'm getting an error that I can't quite follow. The error follows the code below. import httplib, urllib url = "pdb-services-beta.nipr.com" xml = '<?xml version="1.0"?><!DOCTYPE SCB_Request SYSTEM "http://www.nipr.com/html/SCB_XML_Request.dtd"><SCB_Request Request_Type="Create_Report"><SCB_Login_Data CustomerID="someuser" Passwd="somepass" /><SCB_Create_Report_Request Title=""><Producer_List><NIPR_Num_List_XML><NIPR_Num NIPR_Num="8980608" /><NIPR_Num NIPR_Num="7597855" /><NIPR_Num NIPR_Num="10166016" /></NIPR_Num_List_XML></Producer_List></SCB_Create_Report_Request></SCB_Request>' params = {} params['xmldata'] = xml headers = {} headers['Content-type'] = 'text/xml' headers['Accept'] = '*/*' headers['Content-Length'] = "%d" % len(xml) connection = httplib.HTTPSConnection(url) connection.set_debuglevel(1) connection.request("POST", "/pdb-xml-reports/scb_xmlclient.cgi", params, headers) response = connection.getresponse() print response.status, response.reason data = response.read() print data connection.close Here's the error: Traceback (most recent call last): File "C:\Python27\tutorial.py", line 14, in connection.request("POST", "/pdb-xml-reports/scb_xmlclient.cgi", params, headers) File "C:\Python27\lib\httplib.py", line 958, in request self._send_request(method, url, body, headers) File "C:\Python27\lib\httplib.py", line 992, in _send_request self.endheaders(body) File "C:\Python27\lib\httplib.py", line 954, in endheaders self._send_output(message_body) File "C:\Python27\lib\httplib.py", line 818, in _send_output self.send(message_body) File "C:\Python27\lib\httplib.py", line 790, in send self.sock.sendall(data) File "C:\Python27\lib\ssl.py", line 229, in sendall v = self.send(data[count:]) TypeError: unhashable type My log file says that the xmldata parameter is empty. Any ideas?

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• Negative ItemCount in SharePoint Document Library

  - by ccomet

  What can be done about negative numbers in library item counts? ItemCount is a read-only property, what are you supposed to do when it is drastically incorrect? Earlier last week, I was doing some testing involving the copying and moving of files and folders from one document library to another. I was transfering the items from our actual document library to a sandbox "Test" library that I used to run all sorts of object model and workflow testing in before migrating to the public lists and libraries. I noticed that with files, things worked correctly, but when I copied a folder that had a file inside it (using SPFolder.CopyTo()), the item count for the test library did not actually update. Since this testing was mostly playing around, I paid it little heed. Today I was back in the test library to test a different workflow (regarding PDF conversion). While I was there, I decided to delete the folder I left last week since I didn't need it anymore. And that's when I saw the item count for the list drop to -1 in the All Site Content View. When I deleted the new PDF I had just uploaded, it then dropped to -2! I even checked with the object model... getting an instance of the library I checked the ItemCount property... lo and behold it was also -2. Is there any process which runs in the background, kinda like the one that cleans up workflow history, which will correct this kind of issue? Or is a programmer expected to keep watch for this kind of situation and come up with calculations to compensate the "count penalty", as it were?

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• Why were namespaces removed from ECMAScript consideration?

  - by Bob

  Namespaces were once a consideration for ECMAScript (the old ECMAScript 4) but were taken out. As Brendan Eich says in this message: One of the use-cases for namespaces in ES4 was early binding (use namespace intrinsic), both for performance and for programmer comprehension -- no chance of runtime name binding disagreeing with any earlier binding. But early binding in any dynamic code loading scenario like the web requires a prioritization or reservation mechanism to avoid early versus late binding conflicts. Plus, as some JS implementors have noted with concern, multiple open namespaces impose runtime cost unless an implementation works significantly harder. For these reasons, namespaces and early binding (like packages before them, this past April) must go. But I'm not sure I understand all of that. What exactly is a prioritization or reservation mechanism and why would either of those be needed? Also, must early binding and namespaces go hand-in-hand? For some reason I can't wrap my head around the issues involved. Can anyone attempt a more fleshed out explanation? Also, why would namespaces impose runtime costs? In my mind I can't help but see little difference in concept between a namespace and a function using closures. For instance, Yahoo and Google both have YAHOO and google objects that "act like" namespaces in that they contain all of their public and private variables, functions, and objects within a single access point. So why, then, would a namespace be so significantly different in implementation? Maybe I just have a misconception as to what a namespace is exactly.

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• Algorithm design, "randomising" timetable schedule in Python although open to other languages.

  - by S1syphus

  Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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• Building Dynamic Classes in Objective C

  - by kjell_

  I'm a somewhat competent ruby programmer. Yesterday I decided to finally try my hand with Apple's Cocoa frameworks. Help me see things the ObjC way? I'm trying to get my head around objc_allocateClassPair and objc_registerClassPair. My goal is to dynamically generate a few classes and then be able to use them as I would any other class. Does this work in Obj C? Having allocated and registered class A, I get a compile error when calling [[A alloc] init]; (it says 'A' Undeclared). I can only instantiate A using runtime's objc_getClass method. Is there any way to tell the compiler about A and pass it messages like I would NSString? A compiler flag or something? I have 10 or so other classes (B, C, …), all with the same superclass. I want to message them directly in code ([A classMethod], [B classMethod], …) without needing objc_getClass. Am I trying to be too dynamic here or just botching my implementation? It looks something like this… NSString *name = @"test"; Class newClass = objc_allocateClassPair([NSString class], [name UTF8String], 0); objc_registerClassPair(newClass); id a = [[objc_getClass("A") alloc] init]; NSLog(@"new class: %@ superclass: %@", a, [a superclass]); //[[A alloc] init]; blows up.

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• Frame Buster Buster ... buster code needed

  - by Jeff Atwood

  Let's say you don't want other sites to "frame" your site in an <iframe>: <iframe src="http://yourwebsite.com"></iframe> So you insert anti-framing, frame busting JavaScript into all your pages: /* break us out of any containing iframes */ if (top != self) { top.location.replace(self.location.href); } Excellent! Now you "bust" or break out of any containing iframe automatically. Except for one small problem. As it turns out, your frame-busting code can be busted, as shown here: <script type="text/javascript"> var prevent_bust = 0 window.onbeforeunload = function() { prevent_bust++ } setInterval(function() { if (prevent_bust > 0) { prevent_bust -= 2 window.top.location = 'http://server-which-responds-with-204.com' } }, 1) </script> This code does the following: increments a counter every time the browser attempts to navigate away from the current page, via the window.onbeforeonload event handler sets up a timer that fires every millisecond via setInterval(), and if it sees the counter incremented, changes the current location to a server of the attacker's control that server serves up a page with HTTP status code 204, which does not cause the browser to nagivate anywhere My question is -- and this is more of a JavaScript puzzle than an actual problem -- how can you defeat the frame-busting buster? I had a few thoughts, but nothing worked in my testing: attempting to clear the onbeforeunload event via onbeforeonload = null had no effect adding an alert() stopped the process let the user know it was happening, but did not interfere with the code in any way; clicking OK lets the busting continue as normal I can't think of any way to clear the setInterval() timer I'm not much of a JavaScript programmer, so here's my challenge to you: hey buster, can you bust the frame-busting buster?

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• "Best" language /architecture for browser-based app with ODBC and sockets? (subjective)

  - by mawg

  Sorry to ask a subjective question, but I would welcome some advice. I am an experienced programmer of embedded s/w, but haven't done much network programming, although I have done a fair bit of hobbyist PHP. Anyway, I have to develop what is probably a fairly general type of app, as shown in this crude diagram --------------------------------------------------------------------------------- | Browser / user interface Takes input from user form and writes data to d/b. | | Also gets data and updates browser contents when when d/b contents are changed | | because of info received over TCP/IP. | |________________________________________________________________________________| | ODBC | |_______________________________________________________________________________| | database | |_______________________________________________________________________________| | ODBC | |_______________________________________________________________________________| | Socket (TCP/IP) | | Send data out when d/b is updated from browser. | | Also, update d/b when data are received over TCP/IP. | |_______________________________________________________________________________| As I say, I imagine this to be a fairly typical architecture? Am I right? Then client is insisting on MSIE - unless I can show compelling technical reasons for FireFox or other then it will have to be MSIE (are there any compelling technical reasons?). So, with MIE (almost) a given, I had though to use PHP, since I know it, but the client seems awfully keen on Java (which ought to be OK since I am conversant with C++) it woudl seem to make sense to use the same language for the "upper" interface between the web pages (which that app generates) and the d/b, and for the "lower" interface between the d/b and the socket. (a single language means a single set of tools since text approach, etc) So, the (probably highly subjective) question is "which language shoudl I choose". As I say, the client is keen on Java. Any compelling reason why not? Is it generally a good choice for the sort of thing described here? Any other hints & tips gratefully appreciated (and up-voted): URLs, books, tool chain suggestions, etc, etc

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• Best ways to teach a beginner to program?

  - by Justin Standard

  Original Question I am currently engaged in teaching my brother to program. He is a total beginner, but very smart. (And he actually wants to learn). I've noticed that some of our sessions have gotten bogged down in minor details, and I don't feel I've been very organized. (But the answers to this post have helped a lot.) What can I do better to teach him effectively? Is there a logical order that I can use to run through concept by concept? Are there complexities I should avoid till later? The language we are working with is Python, but advice in any language is welcome. How to Help If you have good ones please add the following in your answer: Beginner Exercises and Project Ideas Resources for teaching beginners Screencasts / blog posts / free e-books Print books that are good for beginners Please describe the resource with a link to it so I can take a look. I want everyone to know that I have definitely been using some of these ideas. Your submissions will be aggregated in this post. Online Resources for teaching beginners: A Gentle Introduction to Programming Using Python How to Think Like a Computer Scientist Alice: a 3d program for beginners Scratch (A system to develop programming skills) How To Design Programs Structure and Interpretation of Computer Programs Learn To Program Robert Read's How To Be a Programmer Microsoft XNA Spawning the Next Generation of Hackers COMP1917 Higher Computing lectures by Richard Buckland (requires iTunes) Dive into Python Python Wikibook Project Euler - sample problems (mostly mathematical) pygame - an easy python library for creating games Create Your Own Games With Python ebook Foundations of Programming for a next step beyond basics. Squeak by Example Recommended Print Books for teaching beginners Accelerated C++ Python Programming for the Absolute Beginner Code by Charles Petzold

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• Javascript/Greasemonkey: search for something then set result as a value

  - by thewinchester

  Ok, I'm a bit of a n00b when it comes to JS (I'm not the greatest programmer) so please be gentle - specially if my questions been asked already somewhere and I'm too stupid to find the right answer. Self deprecation out of the way, let's get to the question. Problem There is a site me and a large group of friends frequently use which doesn't display all the information we may like to know - in this case an airline bookings site and the class of travel. While the information is buried in the code of the page, it isn't displayed anywhere to the user. Using a Greasemonkey script, I'd like to liberate this piece of information and display it in a suitable format. Here's the psuedocode of what I'm looking to do. Search dom for specified element define variables Find a string of text If found Set result to a variable Write contents to page at a specific location (before a specified div) If not found Do nothing I think I've achieved most of it so far, except for the key bits of: Searching for the string: The page needs to search for the following piece of text in the page HEAD: mileageRequest += "&CLASSES=S,S-S,S-S"; The Content I need to extract and store is between the second equals (=) sign and the last comma ("). The contents of this area can be any letter between A-Z. I'm not fussed about splitting it up into an array so I could use the elements individually at this stage. Writing the result to a location: Taking that found piece of text and writing it to another location. Code so far This is what I've come up so far, with bits missing highlighted. buttons = document.getElementById('buttons'); ''Search goes here var flightClasses = document.createElement("div"); flightClasses.innerHTML = '<div id="flightClasses"> ' + '<h2>Travel classes</h2>' + 'For the above segments, your flight classes are as follows:' + 'write result here' + '</div>'; main.parentNode.insertBefore(flightClasses, buttons); If anyone could help me, or point me in the right direction to finish this off I'd appreciate it.

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• Is there a perfect algorithm for chess?

  - by Overflown

  Dear Stack Overflow community, I was recently in a discussion with a non-coder person on the possibilities of chess computers. I'm not well versed in theory, but think I know enough. I argued that there could not exist a deterministic Turing machine that always won or stalemated at chess. I think that, even if you search the entire space of all combinations of player1/2 moves, the single move that the computer decides upon at each step is based on a heuristic. Being based on a heuristic, it does not necessarily beat ALL of the moves that the opponent could do. My friend thought, to the contrary, that a computer would always win or tie if it never made a "mistake" move (however do you define that?). However, being a programmer who has taken CS, I know that even your good choices - given a wise opponent - can force you to make "mistake" moves in the end. Even if you know everything, your next move is greedy in matching a heuristic. Most chess computers try to match a possible end game to the game in progress, which is essentially a dynamic programming traceback. Again, the endgame in question is avoidable though. -- thanks, Allan Edit: Hmm... looks like I ruffled some feathers here. That's good. Thinking about it again, it seems like there is no theoretical problem with solving a finite game like chess. I would argue that chess is a bit more complicated than checkers in that a win is not necessarily by numerical exhaustion of pieces, but by a mate. My original assertion is probably wrong, but then again I think I've pointed out something that is not yet satisfactorily proven (formally). I guess my thought experiment was that whenever a branch in the tree is taken, then the algorithm (or memorized paths) must find a path to a mate (without getting mated) for any possible branch on the opponent moves. After the discussion, I will buy that given more memory than we can possibly dream of, all these paths could be found.

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• Metaprogramming - self explanatory code - tutorials, articles, books

  - by elena

  Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into practice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decisions - experience - good decisions)? EDIT: Something of the likes of this example from the Pragmatic Programmer: ...implement a mini-language to control a simple drawing package... The language consists of single-letter commands. Some commands are followed by a single number. For example, the following input would draw a rectangle: P 2 # select pen 2 D # pen down W 2 # draw west 2cm N 1 # then north 1 E 2 # then east 2 S 1 # then back south U # pen up Thank you!

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