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• Which of FILE* or ifstream has better memory usage?

  - by Viet

  I need to read fixed number of bytes from files, whose sizes are around 50MB. To be more precise, read a frame from YUV 4:2:0 CIF/QCIF files (~25KB to ~100KB per frame). Not very huge number but I don't want whole file to be in the memory. I'm using C++, in such a case, which of FILE* or ifstream has better (less/minimal) memory usage? Please kindly advise. Thanks! EDIT: I read fixed number of bytes: 25KB or 100KB (depending on QCIF/CIF format). The reading is in binary mode and forward-only. No seeking needed. No writing needed, only reading. EDIT: If identifying better of them is hard, which one does not require loading the whole file into memory?

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• How much memory is reserved when i declare a string?

  - by Bhagya

  What exactly happens, in terms of memory, when i declare something like: char arr[4]; How many bytes are reserved for arr? How is null string accommodated when I 'strcpy' a string of length 4 in arr? I was writing a socket program, and when I tried to suffix NULL at arr[4] (i.e. the 5th memory location), I ended up replacing the values of some other variables of the program (overflow) and got into a big time mess. Any descriptions of how compilers (gcc is what I used) manage memory?

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• How would I write a virtual CD/DVD burner that would allow programs that burn to write to ISO?

  - by Ryan

  I want to write an app that will allow a program like iTunes which normally will recognize a DVD/CD burner to recognize a virtual one and then write to it creating an ISO. I would guess to use C/C++... can someone point me in the right direction as to how this can be done? Basically it would be a virtual CD/DVD burner that would output an ISO file to the hard drive. I want to do this for both the usefulness of it as well as the challenge, just need an idea of how to approach it, have no idea how to write virtual hardware.

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• How to protect against GHC7 compiled programs taking all memory?

  - by Petr Pudlák

  When playing with various algorithms in Haskell it often happens to me that I create a program with a memory leak, as it often happens with lazy evaluation. The program taking all the memory isn't really fun, I often have difficulty killing it if I realize it too late. When using GHC6 I simply had export GHCRTS='-M384m' in my .bashrc. But in GHC7 they added a security measure that unless a program is compiled with -rtsopts, it simply fails when it is given any RTS option either on a command line argument or in GHCRTS. Unfortunately, almost no Haskell programs are compiled with this flag, so setting this variable makes everything to fail (as I discovered in After upgrading to GHC7, all programs suddenly fail saying "Most RTS options are disabled. Link with -rtsopts to enable them."). Any ideas how to make any use of GHCRTS with GHC7, or another convenient way how to prevent my programs taking all memory?

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• using arrays to get best memory alignment and cache use, is it necessary?

  - by Alberto Toglia

  I'm all about performance these days cause I'm developing my first game engine. I'm no c++ expert but after some research I discovered the importance of the cache and the memory alignment. Basically what I found is that it is recommended to have memory well aligned specially if you need to access them together, for example in a loop. Now, In my project I'm doing my Game Object Manager, and I was thinking to have an array of GameObjects references. meaning I would have the actual memory of my objects one after the other. static const size_t MaxNumberGameObjects = 20; GameObject mGameObjects[MaxNumberGameObjects]; But, as I will be having a list of components per object -Component based design- (Mesh, RigidBody, Transformation, etc), will I be gaining something with the array at all? Anyway, I have seen some people just using a simple std::map for storing game objects. So what do you guys think? Am I better off using a pure component model?

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• Under Windows CE, how can I check which RAM based DLLs are loaded in virtual memory space?

  - by Michal Drozdowicz

  I have a problem with loading a DLL under Windows Mobile 5.0. I'm pretty confident that this is caused by running out of the application virtual memory (the 32 MB slot of the process, as explained in Windows CE .NET Advanced Memory Management). I'm looking for a way to actually make sure that this is the issue and investigate whether my efforts bring expected results. Do you know of a way to check the contents of the virtual memory application slot? Any applications that can help me with this task?

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• Why and How to avoid Event Handler memory leaks ?

  - by gillyb

  Hey There, I just came to realize, by reading some questions and answers on StackOverflow, that adding event handlers using += in C# (or i guess, other .net languages) can cause common memory leaks... I have used event handlers like this in the past many times, and never realized that they can cause, or have caused, memory leaks in my applications. How does this work (meaning, why does this actually cause a memory leak) ? How can I fix this problem ? Is using -= to the same event handler enough ? Are there common design patterns or best practices for handling situations like this ? Example : How am I supposed to handle an application that has many different threads, using many different event handlers to raise several events on the UI ? Are there any good and simple ways to monitor this efficiently in an already built big application ? Thanks in advance!

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• How to override virtual function in good style? [C++]

  - by Knowing me knowing you

  Hi, guys I know this question is very basic but I've met in few publications (websites, books) different style of override virtual function. What I mean is: if I have base class: class Base { public: virtual void f() = 0; }; in some publications I saw that to override this some authors would just say: void f(); and some would still repeat the virtual keyword before void. Which form of overwriting is in good style? Thank you for your answers.

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• Just how much do I want to make virtual?

  - by Alex

  I am writing an abstract superclass where literally every method is going to be overridden. There is some default functionality I could implement, but most of the time it's enough to leave the implementation to the subclass writer. Since just about every method is going to be overwritten, how much should I make virtual and how much should I just leave as regular methods? In the current incarnation, everything is virtual, but I still haven't let this loose to anyone to use, so the design is flexible. What advantages/disadvantages are there to virtual functions? Links to good reading material about this would be appreciated.

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• Shared memory of same DLL in different 32 bit processes is sometimes different in a terminal session

  - by KBrusing

  We have an 32 bit application consisting of some processes. They communicate with shared memory of a DLL used by every process. Shared memory is build with global variables in C++ by "#pragma data_seg ("Shared")". When running this application sometime during starting a new process in addition to an existing (first) process we observe that the shared memory of both processes is not the same. All new started processes cannot communicate with the first process. After stopping all of our processes and restarting the application (with some processes) everything works fine. But sometime or other after successfully starting and finishing new processes the problem occurs again. Running on all other Windows versions or terminal sessions on Windows server 2003 our application never got this problem. Is there any new "feature" on Windows server 2008 that might disturb the hamony of our application?

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• How to manage memory for ios with large csv files?

  - by Pell000

  I'm new to ios development, and I'm running into issues relating to memory management and my approaches to dealing with large datasets. Right now, I am loading the csv files and storing the relevant data as objects in memory at app initialization. Some of the csv files are larger than 1MB, and in total, my app uses about 180MB of memory. This is obviously way too high of a number (unless the info I found is wrong and this is an acceptable number, then please let me know). I feel as though there is a fundamental flaw in my approach: is there a way I can avoid storing the csv files in the project itself? Or, is there a kind of "lazy" loading I can do so that I can simply look up info in the csv file, as opposed to loading all of the data from it at once? Any help would do. I think that I need a new perspective in how to manage this more efficiently.

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• How to interpret output from Linux 'top' command?

  - by Ali

  Following a discussion made HERE about how PHP-FPM consuming memory, I just found a problem in reading the memory in top command. Here is a screenshot of my top just after restarting PHP-FPM. Everything is normal: about 20 PHP-FPM processes, each consuming 5.5MB memory (0.3% of total). Here is the aged server right before restart of PHP-FPM (one day after the previous restart). Here, we still have about 25 PHP-FPM with double memory usage (10MB indicating 0.5% of total). Thus, the total memory used should be 600-700 MB. Then, why 1.6GB memory has been used?

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• IP failover with 2 nodes on different subnet: cannot ping virtual IP from second node?

  - by quanta

  I'm going to setup redundant failover Redmine: another instance was installed on the second server without problem MySQL (running on the same machine with Redmine) was configured as master-master replication Because they are in different subnet (192.168.3.x and 192.168.6.x), it seems that VIPArip is the only choice. /etc/ha.d/ha.cf on node1 logfacility none debug 1 debugfile /var/log/ha-debug logfile /var/log/ha-log autojoin none warntime 3 deadtime 6 initdead 60 udpport 694 ucast eth1 node2.ip keepalive 1 node node1 node node2 crm respawn /etc/ha.d/ha.cf on node2: logfacility none debug 1 debugfile /var/log/ha-debug logfile /var/log/ha-log autojoin none warntime 3 deadtime 6 initdead 60 udpport 694 ucast eth0 node1.ip keepalive 1 node node1 node node2 crm respawn crm configure show: node $id="6c27077e-d718-4c82-b307-7dccaa027a72" node1 node $id="740d0726-e91d-40ed-9dc0-2368214a1f56" node2 primitive VIPArip ocf:heartbeat:VIPArip \ params ip="192.168.6.8" nic="lo:0" \ op start interval="0" timeout="20s" \ op monitor interval="5s" timeout="20s" depth="0" \ op stop interval="0" timeout="20s" \ meta is-managed="true" property $id="cib-bootstrap-options" \ stonith-enabled="false" \ dc-version="1.0.12-unknown" \ cluster-infrastructure="Heartbeat" \ last-lrm-refresh="1338870303" crm_mon -1: ============ Last updated: Tue Jun 5 18:36:42 2012 Stack: Heartbeat Current DC: node2 (740d0726-e91d-40ed-9dc0-2368214a1f56) - partition with quorum Version: 1.0.12-unknown 2 Nodes configured, unknown expected votes 1 Resources configured. ============ Online: [ node1 node2 ] VIPArip (ocf::heartbeat:VIPArip): Started node1 ip addr show lo: 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet 192.168.6.8/32 scope global lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever I can ping 192.168.6.8 from node1 (192.168.3.x): # ping -c 4 192.168.6.8 PING 192.168.6.8 (192.168.6.8) 56(84) bytes of data. 64 bytes from 192.168.6.8: icmp_seq=1 ttl=64 time=0.062 ms 64 bytes from 192.168.6.8: icmp_seq=2 ttl=64 time=0.046 ms 64 bytes from 192.168.6.8: icmp_seq=3 ttl=64 time=0.059 ms 64 bytes from 192.168.6.8: icmp_seq=4 ttl=64 time=0.071 ms --- 192.168.6.8 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3000ms rtt min/avg/max/mdev = 0.046/0.059/0.071/0.011 ms but cannot ping virtual IP from node2 (192.168.6.x) and outside. Did I miss something? PS: you probably want to set IP2UTIL=/sbin/ip in the /usr/lib/ocf/resource.d/heartbeat/VIPArip resource agent script if you get something like this: Jun 5 11:08:10 node1 lrmd: [19832]: info: RA output: (VIPArip:stop:stderr) 2012/06/05_11:08:10 ERROR: Invalid OCF_RESK EY_ip [192.168.6.8] http://www.clusterlabs.org/wiki/Debugging_Resource_Failures Reply to @DukeLion: Which router receives RIP updates? When I start the VIPArip resource, ripd was run with below configuration file (on node1): /var/run/resource-agents/VIPArip-ripd.conf: hostname ripd password zebra debug rip events debug rip packet debug rip zebra log file /var/log/quagga/quagga.log router rip !nic_tag no passive-interface lo:0 network lo:0 distribute-list private out lo:0 distribute-list private in lo:0 !metric_tag redistribute connected metric 3 !ip_tag access-list private permit 192.168.6.8/32 access-list private deny any

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• Strict security and virtual host isolation with Nginx?

  - by Hach-Que

  I currently have an Apache web server set up under which each virtual host is isolated using HTTPD-ITK and the AppArmor module. Each virtual host's workers are setuid/setgid by the server and are then placed in an AppArmor profile. I'm looking to use Nginx but I can't find any documentation on setting it up so that rather than the worker processes being shared between all virtual hosts, worker processes are per virtual host (and thus can be setuid / setgid). Is there any way to do this under Nginx?

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• 'Memory read error',Sever hardware error?

  - by wss8848

  hello I got a error about my server which is running CentOS5.5. MCE 20 HARDWARE ERROR. This is *NOT* a software problem! Please contact your hardware vendor CPU 1 BANK 8 TSC 6ab9ff9745f62 [at 2394 Mhz 9 days 1:50:52 uptime (unreliable)] MISC cf36ad0100081186 ADDR 203376500 MCG status: MCi status: MCi_MISC register valid MCi_ADDR register valid MCA: MEMORY CONTROLLER RD_CHANNELunspecified_ERR Transaction: Memory read error STATUS 8c0000400001009f MCGSTATUS 0 what is the matter? is memory card error or memory controller error?

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• How to deal with 100's or 1000's of virtual hosts

  - by anton

  I am curious to know how services such as heroku manage 1000's of virtual hosts - ie if you create a web site/app, and put it up on these services, you get your own virtual host name - foo.heroku.com etc (the same applies to many other sites that have vanity URLs). I know with various web servers and proxies you can configure as many virtual hosts as you want - but there must be some upper limit to this ? Do they programmatically add virtual hosts - perhaps spreading the load? Or are there other solutions.

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• Apache consuming large memory with Apache Mobile Filter

  - by VarunGupta

  I installed and configured Apache Mobile Filter module for Apache to redirect users to mobile version of our website, depending on their user agents. I configured the module to use WURFL. But as soon as I start Apache it hogs a large amount of memory (without any in-coming web requests): Resident Memory: 300 to 400 MB Virtual Memory: 300 to 650 MB Without this module, Apache was consuming much lesser memory (4 to 10 MB). What could be the reason here?

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• How to retrieve virtual machines from a pool via API in oVirt (RHEV)

  - by FerCa

  In oVirt (Red Hat Enterprise Virtualization) you can create a Virtual Machines Pool to allow your users to retrieve virtual machines from this pool. I found how a user, in the RHEV User Portal, can request a Virtual Machine from the pool, this is explained here: https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Virtualization/3.0/html/Evaluation_Guide/Evaluation_Guide-Allocate_VM.html The thing is that i will need to retrieve virtual machines from the pool with the REST API and, after reading the documentation (https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Virtualization/3.0/html-single/REST_API_Guide/index.html) I cant found the way to do this.

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• Upgrade Ubuntu linux-virtual on EC2

  - by James Ward

  I have an Ubuntu 10.10 EBS boot server on EC2. There are new updates available for it: linux-image-virtual linux-virtual Is it even ok to upgrade those packages on an EC2 server? When I do try to upgrade them I get: The following packages have been kept back: linux-image-virtual linux-virtual Should I do a dist-upgrade or something to force it? Will my instance be able to be rebooted?

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• Can VHD from Virtual PC 2007 be mounted under Virtual Server 2005 R2?

  - by SteveM82

  I have a virtual hard disk file (VHD) created using Microsoft Virtual PC 2007. Can this file be copied to a host running Microsoft Virtual Server 2005 R2 and be used as the basis for creating a new virtual machine? Essentially, are the VHD file formats between the two products compatible, or do I need to create a new VHD from scratch? Thanks.

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• How to prevent virtual machines's copy

  - by Florent

  I'll have to deploy virtual machines on demo laptops, which will use Vmware player, but I've got some security concerns, as some data stored in the virtual machines are a bit sensitive. Is there a way to prevent the copy of these virtual machines ? Are the virtual hard drives encrypted, and if not is there a way to encrypt them ? In short, is there a way to lock down everything so that nobody could copy and or use these VMs in another computer ?

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• Server Vs Service / Physical Vs Virtual

  - by user559142

  When reading definitions for a server service (e.g. iis) you will often find that there are several cross references to a virtual server but none seem to definitively refer to the two as the same..... Can somebody help me to understand the differences - I cannot get my head around what the difference between each is? Ideally I would like to know the differences between the following/or indeed if any refer to the same... 1) Logical Server 2) Virtual Host 3) Logical Partition 4) Physical Server Vs Virtual Server 5) Server Service Vs Virtual Host

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• vmdk to live cd - VMware vmxnet virtual NIC driver Kernel panic

  - by ronalchn

  Task I am trying to convert a virtual machine to a live CD. Specifically, the virtual machine I am trying to convert is the IOI 2013 Competition Environment. In this task, I am aided by a guide Converting a virtual disk image: VDI or VMDK to an ISO you can distribute. Symptoms However, after getting through all the instructions, the live CD causes a kernel panic on boot on bare metal. In particular, the screen shows: [0.737348] cdrom: Uniform CD-ROM driver Revision: 3.20 [0.737503] sr 3:0:0:0: >Attached scsi CD-ROM sr0 [0.737638] sr 3:0:0:0: >Attached scsi generic sg2 type 5 [0.737771] Freeing unused kernel memory: 756k freed [0.738093] Write protecting the kernel text: 5960k [0.738155] Write protecting the kernel read-only data: 2424k [0.738224] NX-protecting the kernel data: 4280k Loading, please wait... [0.752252] udevd[100]: starting version 175 [0.768708] VMware vmxnet3 virtual NIC driver - version 1.1.29.0-k-NAPI [0.781204] VMware PVSCSI driver - version 1.0.2.0-k [0.789555] VMware vmxnet virtual NIC driver [0.799356] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000200 [0.799356] [0.799472] Pid: 1, comm: init Tainted: G 0 3.5.0-17-generic #28-Ubuntu [0.799549] Call Trace: [0.799603] [<c15bf0ec>] panic+0x81/0x17b [0.799654] [<c104a6a5>] do_exit+0x745/0x7a0 [0.799707] [<c104a9a4>] do_group_exit+0x34/0xa0 [0.799760] [<c104aa28>] sys_exit_group+0x18/0x20 [0.799813] [<c15cff5f>] sysenter_do_call+0x12/0x28 Possible problem I suspect that the problem is the VMware vmxnet virtual NIC driver - however, I do not know how I can uninstall it, and possibly install one for a bare metal machine. If anyone knows which packages needs installing/uninstalling at the .rootfs/ chroot directory stage, please let me know. Details on procedure Do note that after importing the .ova file into Virtualbox, the virtual machine is stored as a .vmdk file already, and not a .vdi file. I would like to point out some results of the procedure followed in case of any questions. This is after extracting the filesystem from the .raw file to the .rootfs/ directory mentioned in the blog. I changed the filesystem table as mentioned in the blog, then looked at the possible "kernel optimized for virtualization". However, I found that linux-image-generic was already installed. Also, when running the command dpkg-query --showformat='${Package}\n' -W 'vmware-tools*' (or dpkg-query --showformat='${Package}\n' -W '*-virtual'), no packages were found. Thus, I did not find any virtualization specific packages. I proceeded to generate the iso following the steps in the blog, and burned it to a DVD.

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• How To Configure Remote Desktop To Hyper-V Guest Virtual Machines

  - by Brian Jackett

  Configuring Remote Desktop (RDP) from a host Hyper-V machine to a guest virtual machine can be tricky, so this post is dedicated to the issues and resolution steps I went through to allow RDP.  Cutting to the point, below are the things to look for followed by some explanation about my scenario if you care to read.  This is not an exhaustive list of what is required, just the items that were causing problems for my particular scenario. Requirements Allow Remote Desktop Connections in guest OS. The network adapter type must allow communication with host machine (e.g. use an “Internal” virtual adapter.) If running Server 2008 R2 on guest, network discovery mode must be turned on. If running Server 2008 R2 on guest, the services supporting network discovery mode must be running: - DNS Client - Function Discovery Resource Publication - SSDP Discovery - UPnP Device Host My Environment     A quick word about my environment.  I am running Windows Server 2008 R2 with Hyper V on my laptop and numerous guest VMs running Windows Server 2003 R2 or Windows Server 2008 R2.  I run a domain controller VM and then 1 or 2 SharePoint servers depending on my work needs.  I’ve found this setup to work well except when it comes to the display window for my VMs. The Issue     Ever since I began running Hyper-V I haven’t been able to RDP to my guest VMs which means the resolution for my connection windows ha been limited to what the native Hyper-V connections allow.  During personal use I can put the resolution up to 1152 x 864, but during presentations I am usually limited to a measly 800 x 600.  That is until today when I decided to fully investigate why I couldn’t connect via RDP.     First a thank you to John Ross (@johnrossjr), Christina Wheeler (@cwheeler76) and Clayton Cobb (@warrtalon) for various suggestions while I was researching tonight.  As it turns out I had not 1, not 2, but 3 items preventing me from using RDP.  Let’s dig into the requirements above. Allow RDP Connection     This item I had previously taken care of, but it bears repeating because by default Windows Server 2008 R2 does not allow RDP connections.  Change the setting from “Don’t allow…” to whichever “Allow connections…” setting suits your needs.  I chose the less secure option as this is just my dev laptop. Network Adapter Type     When I originally configured my VMs I configured each to use 2 network adapters: one using the physical ethernet adapter for internet use and a virtual private adapter for communication between the VMs.  The connection for the ethernet adapter is an "”External” adapter and thus doesn’t connect between the host and guest.  The virtual private adapter allowed communication ONLY between the VMs and not to my host.  There is a third option “Internal” which allows communication between VMs as well as to the host.  After finding out this distinction I promptly created an Internal network adapter and assigned that to my VMs. Turn On Network Discovery     Seems like a pretty common sense thing, but in order to allow remote desktop connections the target computer must able to be found by the source computer (explained here.)  One of the settings that controls if a computer can be found on the network is aptly named Network Discovery.  By default Windows Server 2008 R2 turns Network Discovery off for security purposes.  To enable it open up the Network and Sharing Center.  Click “Change Advanced Sharing Settings” on the left.  On the following screen select “Turn on network discovery” for the currently used profile and click Save Settings.  You may notice though that your selection to turn on network discovery doesn’t save.  If this is the case then you most likely don’t have the supporting services running (as was my case.) Network Discovery Supporting Services     There are a total of 4 services (listed again below) that need to be running before you can turn on network discovery (explained here.)  The below images highlight these services.  In my guest VM I found that I had DNS Client already running while the other 3 were disabled.  I set them all to enabled and started the ones that were stopped.  After this change I returned to the Sharing settings screen and found that Network Discovery was turned on.  I’m not sure whether this was picking up my attempt to turn it on previously or if starting those services turned it on.  Either way the end result was a success. - DNS Client - Function Discovery Resource Publication - SSDP Discovery - UPnP Device Host Before and After Results     The first image is the smaller square shaped viewing window used by the Hyper-V native connection.  The second is the full-screen RDP connection in all its widescreen glory. Conclusion     Over the past few months I’ve found Hyper-V to be very useful for virtualizing my development environments, but I’ve also had a steep learning curve to get various items configured just right.  Allowing RDP connections to guest VMs was one area that I hadn’t been able to get right for the longest time.  Now that I resolved these issues I hope that others can avoid the pitfalls that I ran into.  If you know of any other items I left off feel free to let me know.        -Frog Out   Links Turning on Network Discovery http://sqlblog.com/blogs/john_paul_cook/archive/2009/08/15/remote-desktop-connection-on-windows-server-2008-r2.aspx Services required for Network Discovery http://social.technet.microsoft.com/Forums/en-US/winservergen/thread/2e1fea01-3f2b-4c46-a631-a8db34ed4f84

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• Virtual Brown Bag Recap: NuGet, PoshCode, Code Templates

  - by Brian Schroer

  "Virtual Brown Bag" anagrams: Roving Tuba Brawl Lawn Bug Vibrator Rubbing Two Larva Vulgar Rabbi Town A Vibrant Grub Owl Blurting a Bar Vow At this week's Roving Tuba Brawl Virtual Brown Bag meeting: Claudio Lassala asked "What does your work environment look like?" He and several others shared pictures. George Mauer talked about NuGet, .NET's answer to Ruby Gems, and PoshCode, a PowerShell code repository Claudio showed how he uses CodeRush templates to quickly generate unit test code Alan Stevens showed how to do the same thing with Resharper templates For detailed notes, links, and the video recording, go to the VBB wiki page: https://sites.google.com/site/vbbwiki/main_page/2010-12-02

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