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  • Staggering java linux process startup to prevent OOM

    - by ctennis
    I am running a number of java processes on a single Linux machine. From a memory and computing standpoint, everything is fine when things are static. However, periodically we use a configuration management package up upgrade the jar or war files, and restart the java process. The problem is, that is restarts them all relatively quickly, and so we get 10 or so java VMs restarting all at the same time (we use daemontools for the service stops/starts), which wreaks havoc on the machine, in terms of OOMs or just really slow. This is because it's spawning the JVM 10x at the same time. Other than trying to stagger the startups, is there a smarter way of handling this? Maybe a sysctl tuning performance parameters, or a JVM parameter?

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  • Can the expect utility handle a case where the process it spawns also spawns a sub process?

    - by davidparks21
    I'm trying to use expect to handle rsync over an ssh shell, but it gets stuck. If I run my rsync command it works (simplified here): It prompts me for my password and copies files to the server: rsync -e ssh -<other_params> If I then enclose that in expect: expect -d -c "spawn rsync -e ssh -<other_params>" -c "expect password:" -c "send mypass\r" It does not execute properly, the program exists and no files are copied. Even the debug mode isn't giving many clues. My best guess is that rsync is spawning the ssh process, and the ssh process is what needs to be interacted with, but send is picking up the rsync process id and sending the input there. Any thoughts?

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  • optimizing mod_fcgid for a dediciated site

    - by Mike Williams
    i'm using mod_fcgid and I'm trying to find resources on how i can optimize it for running a dedicated website but have had no luck... so far i have: ive got apache2 running and im trying to have php processes spawned and always running so apache does not have to keep spawning them. # Fastcgi configuration for PHP5 LoadModule fcgid_module modules/mod_fcgid.so MaxRequestsPerProcess 5000 # Maximum number of PHP processes. MaxProcessCount 8 # Number of seconds of idle time before a process is terminated IPCCommTimeout 1800 IdleTimeout 1800 AddHandler fcgid-script .php5 .php4 .php .php3 .php2 .phtml FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .php5 FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .php4 FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .php FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .php3 FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .php2 FCGIWrapper /usr/local/cpanel/cgi-sys/php5 .phtml

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  • Apache stops serving requests when connections increase

    - by Gunjan
    The values for MaxClients, ServerLimit etc parameters are quite high (4000). Available RAM on the server is high too (~8G). Load average remains below 1 on a 24 core CPU. But when the number of visitors on the website increase apache just stops serving requests. The apache error log is blank and access log shows no more requests coming in. Restarting apache makes it work again until the number of requests increases again. Any ideas where to start looking? UPDATE Getting the below errors in apache error log on running it with LogLevel Debug [info] server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers), spawning 32 children, there are 479 idle, and 1027 total children

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  • Slides and links for Looking at the Clouds through Dirty Windows :-)

    - by Eric Nelson
    Tomorrow (Friday 23/4/2010) I am delivering a session at the Cloud Grid Exchange in London at SkillsMatter (A top training company and superb supporter of development communities). To be perfectly honest – I’m more interested in attending than presenting as the sessions and speaker line up look great. But in the middle of all that I will be doing the following (rather cheekily named) session: Looking at the Clouds through dirty Windows Many developers assume that the Microsoft Windows Azure Platform for Cloud Computing is only relevant if you develop solutions using Microsoft Visual Studio and the .NET Framework. The reality is somewhat different. In the same way that developers can build great applications on Windows Server using a variety of programming languages, developers can do the same for Azure. Java, Tomcat, PHP, Ruby, Python, MySQL and more all work great on Azure. In this session we will take a lap around the services offered by the Azure PaaS and demonstrate just how easy it is to build and deploy applications built in .NET and other technologies. The session will be a mix of slides and demos – currently I plan to demo .NET and Ruby on Rails running on Azure – but I may flex that depending on how the morning sessions go and who turns up. Looking at the clouds through dirty windows View more presentations from Eric Nelson. Links: Getting started: Details on how to sign up for FREE to try out Windows Azure http://bit.ly/azure25  Getting started with Windows Azure UK Site http://bit.ly/startazure UK Azure Site http://bit.ly/landazure UK Community http://ukazure.ning.com Examples of Azure and none .NET technologies: http://ukinterop.cloudapp.net Restlet based, using Windows Azure Storage http://rubyukinterop.cloudapp.net Rails based clone using Windows Azure Storage (down at time of posting) http://rubysqlazure.cloudapp.net Simple rails using SQL Azure http://bookingbug.com Real world “Ruby on Rails on Azure” (Work in progress for conversion to Azure) Domino’s Pizza migration of Java/Tomcat on Solaris to Java/Tomcat on Windows Azure Main Azure Interop site http://www.microsoft.com/WindowsAzure/interop/: Eclipse Tooling http://windowsazure4e.org Java support http://www.windowsazure4j.org/ Rails on Azure skeleton project for Visual Studio http://code.msdn.com/railsonazure Azure Runme utility for spawning processes http://azurerunme.codeplex.com Feedback www.mygreatwindowsazureidea.com

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  • android game performance regarding timers

    - by iQue
    Im new to the game-dev world and I have a tendancy to over-simplify my code, and sometimes this costs me alot fo memory. Im using a custom TimerTask that looks like this: public class Task extends TimerTask { private MainGamePanel panel; public Task(MainGamePanel panel) { this.panel=panel; } /** * When the timer executes, this code is run. */ public void run() { panel.createEnemies(); } } this task calls this method from my view: public void createEnemies() { Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.female); if(enemyCounter < 24){ enemies.add(new Enemy(bmp, this)); } enemyCounter++; } Since I call this in the onCreate-method instead of in my views contructor (because My enemies need to get width and height of view). Im wondering if this will work when I have multiple levels in game (start a new intent). And if this kind of timer really is the best way to add a delay between the spawning-time of my enemies performance-wise. adding code for my timer if any1 came here cus they dont understand timers: private Timer timer1 = new Timer(); private long delay1 = 5*1000; // 5 sec delay public void surfaceCreated(SurfaceHolder holder) { timer1.schedule(new Task(this), 0, delay1); //I call my timer and add the delay thread.setRunning(true); thread.start(); }

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  • Making an interactive 2D map

    - by Chad
    So recently I have been working on a Legend of Zelda: A Link to the Past clone, and I am wondering how I could handle certain map interactions (like cutting grass, lifting rocks, etc). The way I am currently doing the tilemap is with 2 PNGs. The first is the "tilemap" where each pixel represents a 16x16 tile and the (red, green) values are the (x, y) coords for the tile in the second PNG (the "tileset"). I am then using the blue channel to store collision data. Each tile is split into 4 8x8 tiles and represented by a 2 bit value (0 = empty, 1 = Jumpdown point, 2 = unused right now, 3 = blocking). 4 of these 2 bit values make up the full blue channel (1 byte). So collisions work great, and I am moving on to putting interactive units on the level; but I am not sure what a good way is to do it. I have experimented with spawning an entity for each grass and rock, but there are just WAY to many; FPS just dies even if I confine it to the current "zone" the user is in (for those who remember LTTP it had zones you moved between). It does make a difference that this is a browser-based JavaScript game. tl;dr: What is a good way to have an interactive map without using full blown entities for each interactive item?

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  • juju -v status ERROR Invalid SSH key

    - by Captain T
    root@cloudcontrol:/storage# juju -v status 2012-06-07 11:19:47,602 DEBUG Initializing juju status runtime 2012-06-07 11:19:47,621 INFO Connecting to environment... 2012-06-07 11:19:47,905 DEBUG Connecting to environment using node-386077143930... 2012-06-07 11:19:47,906 DEBUG Spawning SSH process with remote_user="ubuntu" remote_host="node-386077143930" remote_port="2181" local_port="57004". The authenticity of host 'node-386077143930 (10.5.5.113)' can't be established. ECDSA key fingerprint is 31:94:89:62:69:83:24:23:5f:02:70:53:93:54:b1:c5. Are you sure you want to continue connecting (yes/no)? yes 2012-06-07 11:19:52,102 ERROR Invalid SSH key 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.5 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@662: Client environment:host.name=cloudcontrol 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@669: Client environment:os.name=Linux 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@670: Client environment:os.arch=3.2.0-23-generic 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@671: Client environment:os.version=#36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@679: Client environment:user.name=sysadmin 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@687: Client environment:user.home=/root 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@699: Client environment:user.dir=/storage 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=localhost:57004 sessionTimeout=10000 watcher=0x7feb11afc6b0 sessionId=0 sessionPasswd= context=0x2dc7d20 flags=0 2012-06-07 11:19:52,429:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-06-07 11:19:55,765:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client This is from a clean install with 2 nodes all running 12.04 Precise juju bootstrap - finishes with no errors and allocates the machine to the user but still no joy after juju environment-destroy and rebuild with different users and different nodes. Anyone got any ideas

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  • Invalid SSH key erron in juju

    - by Captain T
    This is the output of juju from a clean install with 2 nodes all running 12.04 Precise juju bootstrap - finishes with no errors and allocates the machine to the user but still no joy after juju environment-destroy and rebuild with different users and different nodes. root@cloudcontrol:/storage# juju -v status 2012-06-07 11:19:47,602 DEBUG Initializing juju status runtime 2012-06-07 11:19:47,621 INFO Connecting to environment... 2012-06-07 11:19:47,905 DEBUG Connecting to environment using node-386077143930... 2012-06-07 11:19:47,906 DEBUG Spawning SSH process with remote_user="ubuntu" remote_host="node-386077143930" remote_port="2181" local_port="57004". The authenticity of host 'node-386077143930 (10.5.5.113)' can't be established. ECDSA key fingerprint is 31:94:89:62:69:83:24:23:5f:02:70:53:93:54:b1:c5. Are you sure you want to continue connecting (yes/no)? yes 2012-06-07 11:19:52,102 ERROR Invalid SSH key 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.5 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@662: Client environment:host.name=cloudcontrol 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@669: Client environment:os.name=Linux 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@670: Client environment:os.arch=3.2.0-23-generic 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@671: Client environment:os.version=#36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@679: Client environment:user.name=sysadmin 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@687: Client environment:user.home=/root 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@699: Client environment:user.dir=/storage 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=localhost:57004 sessionTimeout=10000 watcher=0x7feb11afc6b0 sessionId=0 sessionPasswd=<null> context=0x2dc7d20 flags=0 2012-06-07 11:19:52,429:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-06-07 11:19:55,765:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client

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  • How to simulate pressure with particles?

    - by BeachRunnerJoe
    I'm trying to simulate pressure with a collection of spherical particles in a Unity game I'm building. A couple notes about the problem: The goal is to fill a constantly changing 2d space/void with small, frictionless spheres. The game is trying to simulate the ever-growing pressure of more objects being shoved into this space. The level itself is constantly scrolling from left to right, meaning if the space's dimensions are not changed by the user it will automatically get smaller (the leftmost part of the space will continually scroll off-screen). I'm wondering what some approaches are that I can take to tackling these problems... Knowing when to detect when there is space to fill and then add spheres to the space. Removing spheres from the space when it is shrinking. Strategies to simulate pressure on the spheres such that they "explode outwards" when more space is created. The current approach I am contemplating is using a constantly moving wall, that is off screen and moves with the screen, as this image illustrates: . This moving wall will push and trap the spheres into the space. As for adding new spheres, I was going to have either (1) spheres replicate themselves upon detecting free space, OR (2) spawn them at the left side of the space (where the wall is) - pushing the rest of the spheres to fill the space. I foresee problems with idea #1 because this likely wouldn't really create/simulate pressure; idea #2 seems more promising, but raises the question of how to provide a location for these new sphere particles to spawn (and the ramifications of spawning them when there IS no space). Thanks so much in advance for your wisdom!

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  • Setting Krypton Light to Screen Pixels

    - by Adam Jerrett
    So a few days back, I started playing around with Krypton XNA for 2D lighting in my game. I noticed in general, that spawning a light at (0,0) with Krypton causes the light to appear in, pretty much, the centre of the game screen. Is there any way to change this so a Krypton light's "starting point" at [0,0] would spawn at the top left of the screen, and thus follow the standard screen co-ordinates for position? I ask because currently I'm busy working on my game where my spawn point is [512,512]. With hard code, the closest I've got to the light being "central" to this point is the vector position [12,-20], which makes no sense and is impossible to craft, mathematically, if I want the light to move with the camera (the position [480,512] maps roughly to [10,-20]). So, is there any way to "normalise" the krypton lights to use standard screen co-ordinates? If you guys can, play around with the demo from the site and please see if you can find anything out about it. Documentation on the engine is rather scarce, so it's difficult to find anything relevant to my "pixel-perfect" need. It might just also be something in the code with regards to the matrices that I'm not fully understanding. Any help would be useful. Thanks.

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  • Agile Data Book from O'Reilly Media

    - by Compudicted
    Originally posted on: http://geekswithblogs.net/Compudicted/archive/2013/07/01/153309.aspxAs part of my ongoing self-education and approaching of some free time, yeah, both is a must for every IT person and geek! I have carefully examined the latest trends in the Computersphere with whatever tools I had at my disposal (nothing really fancy was used) and came to a conclusion that for a database pro the *hottest* topic today is undoubtedly the #BigData and all the rapidly growing and spawning ecosystem around it. Having recently immersed myself into the NoSQL world (let me tell here right away NoSQL means Not Only SQL) one book really stood out of the crowd: Book site: http://shop.oreilly.com/product/0636920025054.doDespite being a new book I am sure it will end up on the tables of many Big Data Generalists.In a few dozen words, it is primarily for two reasons:1) The author understands that a  typical business today cannot wait for a Data Scientist for too long to deliver results demanding as usual a very quick turnaround on investments (ROI), and 2) The book covers all the needed and proven modern brick and mortar offerings to get the job done by a relatively newcomer to the Big Data World.It certainly enables such a professional to grow and expand based on the acquired knowledge, and one can truly do it very fast.

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  • How to properly multi thread an RPG

    - by Nagrom_17
    I am working on an RPG type game in Java and I would like to know a few things relating to threading, What is the best way to implement a "wait for this then do this" without hanging the whole thread? Like waiting for a player to move to a location then pick up an item? or to wait one second then attack? Currently I am spawning new threads every time I need to wait for something, but that doesn't feel like the best solution. Any help is appreciated. EDIT: Clarification and an example of how I currently do things. User clicks on an item The function walkToAndPickUp(item) is called which is basically this: Make a new thread so we don't freeze the thread handling input while the player moves. Tell player to move to the item While the player is not at the item(The player moves through an update() function called in a different thread, I don't know how else to do it without freezing threads) Repeat until the player is at the item If the player is at the item then call delete item from map and add to inventory.

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  • Ubuntu 13.10 Unity doesn't load after upgrade

    - by William
    Just upgraded to Ubuntu 13.10 only to find that Unity won't load (login freezes, after doing ctrl+alt+F1, logging in and then doing startx, I get a blank desktop and the mouse pointer, and nothing else). I can right click, but the only operations that work are "create new file" and "create new folder". For example, "change desktop background" doesn't work. Also, after doing a few right clicks and choosing "change desktop background", I get a warning message box: "compiz closed unexpectedly." Guest login works fine. Tried creating a new user, but I experience the same thing with the new user. Tried removing all configuration files from my home directory... same thing. Doing dconf reset -f /org/compiz/ gives an error "error spawning command line..." Doing unity --reset also gives errors. Tried uninstalling unity (and compiz) and reinstalling, but that doesn't help. Tried reconfiguring lightdm, didn't help. I don't have any proprietary drivers installed. Once again, the funny thing is that the guest session works fine.

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  • Trac FastCGI + Python on dreamhost leaves zombie python running

    - by Katsuke
    Hello there, Recently I installed trac in one of my dreamhost domains. I followed the instructions of http://trac.mlalonde.net/wiki/CreamyTrac and everything worked perfectly. At least i thought that was the case. After a few days, i started to notice that i was getting random 500 pages. I quickly checked the error log, and found a bunch of: [Fri Apr 16 14:35:34 2010] [error] [client *.*.*.*] Premature end of script headers: dispatch.fcgi [Fri Apr 16 14:35:54 2010] [error] [client *.*.*.*] Premature end of script headers: dispatch.fcgi, referer: http://www.trac.****.com/login [Fri Apr 16 16:05:58 2010] [error] [client *.*.*.*] Premature end of script headers: dispatch.fcgi, referer: http://www.trac.****.com/timeline The trac instance has very low traffic so it is possible that this might have been triggered faster if there was more use of it. So next step i went to look at top and am amazed by what i see: (this is NOT exactly what i saw, i just reproduced this from memory) 23730 rl_inst 20 0 44516 15m 4012 S 0.0 0.4 0:00.17 python2.4 23731 rl_inst 20 0 44616 15m 4012 S 0.0 0.4 0:03.17 python2.4 23732 rl_inst 20 0 44116 15m 4012 S 0.0 0.4 0:01.17 python2.4 23733 rl_inst 20 0 44826 15m 4012 S 0.0 0.4 0:04.17 python2.4 23734 rl_inst 20 0 44216 15m 4012 S 0.0 0.4 0:02.17 python2.4 23735 rl_inst 20 0 44416 15m 4012 S 0.0 0.4 0:01.17 python2.4 I opened the trac site again and that changed to this: 23730 rl_inst 20 0 44516 15m 4012 S 0.0 0.4 0:00.17 python2.4 23731 rl_inst 20 0 44616 15m 4012 S 0.0 0.4 0:03.17 python2.4 23732 rl_inst 20 0 44116 15m 4012 S 0.0 0.4 0:01.17 python2.4 23733 rl_inst 20 0 44826 15m 4012 S 0.0 0.4 0:04.17 python2.4 23734 rl_inst 20 0 44216 15m 4012 S 0.0 0.4 0:02.17 python2.4 23735 rl_inst 20 0 44416 15m 4012 S 0.0 0.4 0:01.17 python2.4 28378 rl_inst 20 0 2608 1208 1008 S 0.0 0.0 0:00.00 dispatch.fcgi 28382 rl_inst 20 0 44248 15m 4012 S 0.0 0.4 0:02.19 python2.4 So the dispatch.fcgi was being called correctly and was spawning correctly other python2.4 process. After the IDLE time passed this is the results: 23730 rl_inst 20 0 44516 15m 4012 S 0.0 0.4 0:00.17 python2.4 23731 rl_inst 20 0 44616 15m 4012 S 0.0 0.4 0:03.17 python2.4 23732 rl_inst 20 0 44116 15m 4012 S 0.0 0.4 0:01.17 python2.4 23733 rl_inst 20 0 44826 15m 4012 S 0.0 0.4 0:04.17 python2.4 23734 rl_inst 20 0 44216 15m 4012 S 0.0 0.4 0:02.17 python2.4 23735 rl_inst 20 0 44416 15m 4012 S 0.0 0.4 0:01.17 python2.4 28382 rl_inst 20 0 44248 15m 4012 S 0.0 0.4 0:02.19 python2.4 dispatch.fcgi was gone but the corresponding python2.4 was still there o_O. I had started with 5 sleeping processes of python and after idle time i ended up with 6. I repeated this and found that it kept spawning more and more python2.4, this was indeed what was causing my 500s indirectly. Let me explain my findings. Am on a shared hosting so my processes get killed if they are way too many. So everytime i opened trac 2 new processes spawned and one remained, to the point that dreamhost was killing a random process when i reached my limit. Sometimes killing the python2.4 that actually was rendering the current page. Hence header premature ending, python is gone the .fcgi doesnt know what to do and throws an 500. I found a dirty solution to this. I changed my dispatch.fcgi to contain a line that killed any currently running python2.4 process and then spawn a new one. Since then i dont get any rogues what so ever. But i dont think this is the best solution, calling killall in every fcgi just seems wrong. Anyone has run into this issue and found a cleaner solution? Is there anything that i have overlooked?

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  • How to Run Low-Cost Minecraft on a Raspberry Pi for Block Building on the Cheap

    - by Jason Fitzpatrick
    We’ve shown you how to run your own blocktastic personal Minecraft server on a Windows/OSX box, but what if you crave something lighter weight, more energy efficient, and always ready for your friends? Read on as we turn a tiny Raspberry Pi machine into a low-cost Minecraft server you can leave on 24/7 for around a penny a day. Why Do I Want to Do This? There’s two aspects to this tutorial, running your own Minecraft server and specifically running that Minecraft server on a Raspberry Pi. Why would you want to run your own Minecraft server? It’s a really great way to extend and build upon the Minecraft play experience. You can leave the server running when you’re not playing so friends and family can join and continue building your world. You can mess around with game variables and introduce mods in a way that isn’t possible when you’re playing the stand-alone game. It also gives you the kind of control over your multiplayer experience that using public servers doesn’t, without incurring the cost of hosting a private server on a remote host. While running a Minecraft server on its own is appealing enough to a dedicated Minecraft fan, running it on the Raspberry Pi is even more appealing. The tiny little Pi uses so little resources that you can leave your Minecraft server running 24/7 for a couple bucks a year. Aside from the initial cost outlay of the Pi, an SD card, and a little bit of time setting it up, you’ll have an always-on Minecraft server at a monthly cost of around one gumball. What Do I Need? For this tutorial you’ll need a mix of hardware and software tools; aside from the actual Raspberry Pi and SD card, everything is free. 1 Raspberry Pi (preferably a 512MB model) 1 4GB+ SD card This tutorial assumes that you have already familiarized yourself with the Raspberry Pi and have installed a copy of the Debian-derivative Raspbian on the device. If you have not got your Pi up and running yet, don’t worry! Check out our guide, The HTG Guide to Getting Started with Raspberry Pi, to get up to speed. Optimizing Raspbian for the Minecraft Server Unlike other builds we’ve shared where you can layer multiple projects over one another (e.g. the Pi is more than powerful enough to serve as a weather/email indicator and a Google Cloud Print server at the same time) running a Minecraft server is a pretty intense operation for the little Pi and we’d strongly recommend dedicating the entire Pi to the process. Minecraft seems like a simple game, with all its blocky-ness and what not, but it’s actually a pretty complex game beneath the simple skin and required a lot of processing power. As such, we’re going to tweak the configuration file and other settings to optimize Rasbian for the job. The first thing you’ll need to do is dig into the Raspi-Config application to make a few minor changes. If you’re installing Raspbian fresh, wait for the last step (which is the Raspi-Config), if you already installed it, head to the terminal and type in “sudo raspi-config” to launch it again. One of the first and most important things we need to attend to is cranking up the overclock setting. We need all the power we can get to make our Minecraft experience enjoyable. In Raspi-Config, select option number 7 “Overclock”. Be prepared for some stern warnings about overclocking, but rest easy knowing that overclocking is directly supported by the Raspberry Pi foundation and has been included in the configuration options since late 2012. Once you’re in the actual selection screen, select “Turbo 1000MhHz”. Again, you’ll be warned that the degree of overclocking you’ve selected carries risks (specifically, potential corruption of the SD card, but no risk of actual hardware damage). Click OK and wait for the device to reset. Next, make sure you’re set to boot to the command prompt, not the desktop. Select number 3 “Enable Boot to Desktop/Scratch”  and make sure “Console Text console” is selected. Back at the Raspi-Config menu, select number 8 “Advanced Options’. There are two critical changes we need to make in here and one option change. First, the critical changes. Select A3 “Memory Split”: Change the amount of memory available to the GPU to 16MB (down from the default 64MB). Our Minecraft server is going to ruin in a GUI-less environment; there’s no reason to allocate any more than the bare minimum to the GPU. After selecting the GPU memory, you’ll be returned to the main menu. Select “Advanced Options” again and then select A4 “SSH”. Within the sub-menu, enable SSH. There is very little reason to keep this Pi connected to a monitor and keyboard, by enabling SSH we can remotely access the machine from anywhere on the network. Finally (and optionally) return again to the “Advanced Options” menu and select A2 “Hostname”. Here you can change your hostname from “raspberrypi” to a more fitting Minecraft name. We opted for the highly creative hostname “minecraft”, but feel free to spice it up a bit with whatever you feel like: creepertown, minecraft4life, or miner-box are all great minecraft server names. That’s it for the Raspbian configuration tab down to the bottom of the main screen and select “Finish” to reboot. After rebooting you can now SSH into your terminal, or continue working from the keyboard hooked up to your Pi (we strongly recommend switching over to SSH as it allows you to easily cut and paste the commands). If you’ve never used SSH before, check out how to use PuTTY with your Pi here. Installing Java on the Pi The Minecraft server runs on Java, so the first thing we need to do on our freshly configured Pi is install it. Log into your Pi via SSH and then, at the command prompt, enter the following command to make a directory for the installation: sudo mkdir /java/ Now we need to download the newest version of Java. At the time of this publication the newest release is the OCT 2013 update and the link/filename we use will reflect that. Please check for a more current version of the Linux ARMv6/7 Java release on the Java download page and update the link/filename accordingly when following our instructions. At the command prompt, enter the following command: sudo wget --no-check-certificate http://www.java.net/download/jdk8/archive/b111/binaries/jdk-8-ea-b111-linux-arm-vfp-hflt-09_oct_2013.tar.gz Once the download has finished successfully, enter the following command: sudo tar zxvf jdk-8-ea-b111-linux-arm-vfp-hflt-09_oct_2013.tar.gz -C /opt/ Fun fact: the /opt/ directory name scheme is a remnant of early Unix design wherein the /opt/ directory was for “optional” software installed after the main operating system; it was the /Program Files/ of the Unix world. After the file has finished extracting, enter: sudo /opt/jdk1.8.0/bin/java -version This command will return the version number of your new Java installation like so: java version "1.8.0-ea" Java(TM) SE Runtime Environment (build 1.8.0-ea-b111) Java HotSpot(TM) Client VM (build 25.0-b53, mixed mode) If you don’t see the above printout (or a variation thereof if you’re using a newer version of Java), try to extract the archive again. If you do see the readout, enter the following command to tidy up after yourself: sudo rm jdk-8-ea-b111-linux-arm-vfp-hflt-09_oct_2013.tar.gz At this point Java is installed and we’re ready to move onto installing our Minecraft server! Installing and Configuring the Minecraft Server Now that we have a foundation for our Minecraft server, it’s time to install the part that matter. We’ll be using SpigotMC a lightweight and stable Minecraft server build that works wonderfully on the Pi. First, grab a copy of the the code with the following command: sudo wget http://ci.md-5.net/job/Spigot/lastSuccessfulBuild/artifact/Spigot-Server/target/spigot.jar This link should remain stable over time, as it points directly to the most current stable release of Spigot, but if you have any issues you can always reference the SpigotMC download page here. After the download finishes successfully, enter the following command: sudo /opt/jdk1.8.0/bin/java -Xms256M -Xmx496M -jar /home/pi/spigot.jar nogui Note: if you’re running the command on a 256MB Pi change the 256 and 496 in the above command to 128 and 256, respectively. Your server will launch and a flurry of on-screen activity will follow. Be prepared to wait around 3-6 minutes or so for the process of setting up the server and generating the map to finish. Future startups will take much less time, around 20-30 seconds. Note: If at any point during the configuration or play process things get really weird (e.g. your new Minecraft server freaks out and starts spawning you in the Nether and killing you instantly), use the “stop” command at the command prompt to gracefully shutdown the server and let you restart and troubleshoot it. After the process has finished, head over to the computer you normally play Minecraft on, fire it up, and click on Multiplayer. You should see your server: If your world doesn’t popup immediately during the network scan, hit the Add button and manually enter the address of your Pi. Once you connect to the server, you’ll see the status change in the server status window: According to the server, we’re in game. According to the actual Minecraft app, we’re also in game but it’s the middle of the night in survival mode: Boo! Spawning in the dead of night, weaponless and without shelter is no way to start things. No worries though, we need to do some more configuration; no time to sit around and get shot at by skeletons. Besides, if you try and play it without some configuration tweaks first, you’ll likely find it quite unstable. We’re just here to confirm the server is up, running, and accepting incoming connections. Once we’ve confirmed the server is running and connectable (albeit not very playable yet), it’s time to shut down the server. Via the server console, enter the command “stop” to shut everything down. When you’re returned to the command prompt, enter the following command: sudo nano server.properties When the configuration file opens up, make the following changes (or just cut and paste our config file minus the first two lines with the name and date stamp): #Minecraft server properties #Thu Oct 17 22:53:51 UTC 2013 generator-settings= #Default is true, toggle to false allow-nether=false level-name=world enable-query=false allow-flight=false server-port=25565 level-type=DEFAULT enable-rcon=false force-gamemode=false level-seed= server-ip= max-build-height=256 spawn-npcs=true white-list=false spawn-animals=true texture-pack= snooper-enabled=true hardcore=false online-mode=true pvp=true difficulty=1 player-idle-timeout=0 gamemode=0 #Default 20; you only need to lower this if you're running #a public server and worried about loads. max-players=20 spawn-monsters=true #Default is 10, 3-5 ideal for Pi view-distance=5 generate-structures=true spawn-protection=16 motd=A Minecraft Server In the server status window, seen through your SSH connection to the pi, enter the following command to give yourself operator status on your Minecraft server (so that you can use more powerful commands in game, without always returning to the server status window). op [your minecraft nickname] At this point things are looking better but we still have a little tweaking to do before the server is really enjoyable. To that end, let’s install some plugins. The first plugin, and the one you should install above all others, is NoSpawnChunks. To install the plugin, first visit the NoSpawnChunks webpage and grab the download link for the most current version. As of this writing the current release is v0.3. Back at the command prompt (the command prompt of your Pi, not the server console–if your server is still active shut it down) enter the following commands: cd /home/pi/plugins sudo wget http://dev.bukkit.org/media/files/586/974/NoSpawnChunks.jar Next, visit the ClearLag plugin page, and grab the latest link (as of this tutorial, it’s v2.6.0). Enter the following at the command prompt: sudo wget http://dev.bukkit.org/media/files/743/213/Clearlag.jar Because the files aren’t compressed in a .ZIP or similar container, that’s all there is to it: the plugins are parked in the plugin directory. (Remember this for future plugin downloads, the file needs to be whateverplugin.jar, so if it’s compressed you need to uncompress it in the plugin directory.) Resart the server: sudo /opt/jdk1.8.0/bin/java -Xms256M -Xmx496M -jar /home/pi/spigot.jar nogui Be prepared for a slightly longer startup time (closer to the 3-6 minutes and much longer than the 30 seconds you just experienced) as the plugins affect the world map and need a minute to massage everything. After the spawn process finishes, type the following at the server console: plugins This lists all the plugins currently active on the server. You should see something like this: If the plugins aren’t loaded, you may need to stop and restart the server. After confirming your plugins are loaded, go ahead and join the game. You should notice significantly snappier play. In addition, you’ll get occasional messages from the plugins indicating they are active, as seen below: At this point Java is installed, the server is installed, and we’ve tweaked our settings for for the Pi.  It’s time to start building with friends!     

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  • Recursion causes exit to exit all JFrames (terminates app)

    - by Trizicus
    I have made an application that gives the user the option to open up a new spawn of the application entirely. When the user does so and closes the application the entire application terminates; not just the window. How should I go about recursively spawning an application and then when the user exits the JFrame spawn; killing just that JFrame and not the entire instance? Here is the relevant code: [...] JMenuItem newMenuItem = new JMenuItem ("New"); newMenuItem.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { new MainWindow(); } }); fileMenu.add(newMenuItem); [....] JMenuItem exit = new JMenuItem("Exit"); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } }); fileMenu.add(exit); [...]

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  • Is using ReaderWriterLockSlim a bad idea for long lived objects?

    - by uriDium
    I am trying to track down the reason that an application has periods of bad performance. I think that I have linked the bad performance to the points where Garbage Collection is run for Gen 2. I get a profiling tool (CLR Profiler) and was quite surprised by the results. In my test I was spawning and processing millions of objects. However the biggest hog of the Gen 2 space comes from something Called Threading.ReaderWriterCount which comes from System.Threading.ReaderWriterLockSlim::InitializeThreadCounts. I know nothing about the inner workings of ReaderWriterLockSlim but from what I am getting from the reports it is okay to have 1 or 2 Locks for longer lived objects but try and use other locks if you are going to have many smaller objects. Does anyone have any comments or experience with ReaderWriterLockSlim and/or what to look for if it seems that GC is killing application performance?

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  • Running another ruby script from a ruby script

    - by Andrew Grimm
    In ruby, is it possible to specify to call another ruby script using the same ruby interpreter as the original script is being run by? For example, if a.rb runs b.rb a couple of times, is it possible to replace system("ruby", "b.rb", "foo", "bar") with something like run_ruby("b.rb", "foo", "bar") so that if you used ruby1.9.1 a.rb on the original, ruby1.9.1 would be used on b.rb, but if you just used ruby a.rb on the original, ruby would be used on b.rb? I'd prefer not to use shebangs, as I'd like it to be able to run on different computers, some of which don't have /usr/bin/env. Edit: I didn't mean load or require and the like, but spawning new processes (so I can use multiple CPUs).

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  • iPhone: NSOperationQueue running operations serially

    - by Greg Maletic
    I have a singleton NSOperationQueue that handles all of my network requests. I'm noticing, however, that when I have one particularly long operation running (this particular operation takes at least 25 seconds), my other operations don't run until it completes. maxConcurrentOperationCount is set to NSOperationQueueDefaultMaxConcurrentOperationCount, so I don't believe that's the issue. Any reason why this would be happening? Besides spawning multiple NSOperationQueues (a solution that I'm not sure would work, nor am I sure it's a good idea), what's the best way to fix this problem? Thanks.

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  • Multiprocessing Bomb

    - by iKarampa
    I was working the following example from Doug Hellmann tutorial on multiprocessing: import multiprocessing def worker(): """worker function""" print 'Worker' return if __name__ == '__main__': jobs = [] for i in range(5): p = multiprocessing.Process(target=worker) jobs.append(p) p.start() When I tried to run it outside the if statement: import multiprocessing def worker(): """worker function""" print 'Worker' jobs = [] for i in range(5): p = multiprocessing.Process(target=worker) jobs.append(p) p.start() It started spawning processes non-stop, without any way of to terminating it. Why would that happen? Why it did not generate 5 processes and exit? Why do I need the if statement?

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  • Avoding multiple thread spawns in pthreads

    - by madman
    Hi StackOverflow, I have an application that is parallellized using pthreads. The application has a iterative routine call and a thread spawn within the rountine (pthread_create and pthread_join) to parallelize the computation intensive section in the routine. When I use an instrumenting tool like PIN to collect the statistics the tool reports statistics for several threads(no of threads x no of iterations). I beleive it is because it is spawning new set of threads each time the routine is called. How can I ensure that I create the thread only once and all successive calls use the threads that have been created first. When I do the same with OpenMP and then try to collect the statistics, I see that the threads are created only once. Is it beacause of the OpenMP runtime ? Thanks.

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  • How to get application to use specific version of .NET?

    - by HN
    Hi, I am using pnunit to run nunit tests on remote machines, the pnunit agent loads the test and runs it in Windows 2008 but the test fails to load in Windows 2003, the agent error is INFO PNUnit.Agent.PNUnitAgent - Registering channel on port 9080 INFO PNUnit.Agent.PNUnitAgent - RunTest called for Test MyTest, AssemblyName test.dll, TestToRun test.Program.myDeployTest INFO PNUnit.Agent.PNUnitTestRunner - Spawning a new thread INFO PNUnit.Agent.PNUnitTestRunner - Thread entered for Test MyTest:test.Program.myDeployTest Assembly test.dll Unhandled Exception: System.BadImageFormatException: The format of the file 'test ' is invalid. File name: "test" Server stack trace: at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, B oolean isStringized, Evidence assemblySecurity, Boolean throwOnFileNotFound, Ass embly locationHint, StackCrawlMark& stackMark) On running procmon and monitoring the agent process i could see that the agent executable was using .NET 1.1 assemblies on Windows 2003 and .NET 2.0 on Windows 2008 which could be an explanation for this behavior. How do I get the agent to use .NET 2.0 on Windows 2003?

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  • Long running, polling, queueing process for Python. What's the best stuff to use?

    - by Bialecki
    Feel free to close and/or redirect if this has been asked, but here's my situation: I've got an application that will require doing a bunch of small units of work (polling a web service until something is done, then parsing about 1MB worth of XML and putting it in a database). I want to have a simple async queueing mechanism that'll poll for work to do in a queue, execute the units of work that need to be done, and have the flexibility to allow for spawning multiple worker processes so these units of work can be done in parallel. (Bonus if there's some kind of event framework that would also me to listen for when work is complete.) I'm sure there is stuff to do this. Am I describing Twisted? I poked through the documentation, I'm just not sure exactly how my problems maps onto their framework, but I haven't spent much time with it. Should I just look at the multiprocess libraries in Python? Something else?

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  • What is the "task" in twitter Storm parallelism

    - by John Wang
    I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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