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  • When virtual inheritance IS a good design?

    - by 7vies
    EDIT3: Please be sure to clearly understand what I am asking before answering (there are EDIT2 and lots of comments around). There are (or were) many answers which clearly show misunderstanding of the question (I know that's also my fault, sorry for that) Hi, I've looked over the questions on virtual inheritance (class B: public virtual A {...}) in C++, but did not find an answer to my question. I know that there are some issues with virtual inheritance, but what I'd like to know is in which cases virtual inheritance would be considered a good design. I saw people mentioning interfaces like IUnknown or ISerializable, and also that iostream design is based on virtual inheritance. Would those be good examples of a good use of virtual inheritance, is that just because there is no better alternative, or because virtual inheritance is the proper design in this case? Thanks. EDIT: To clarify, I'm asking about real-life examples, please don't give abstract ones. I know what virtual inheritance is and which inheritance pattern requires it, what I want to know is when it is the good way to do things and not just a consequence of complex inheritance. EDIT2: In other words, I want to know when the diamond hierarchy (which is the reason for virtual inheritance) is a good design

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  • Question about Virtual Inheritance hierarchy

    - by Summer_More_More_Tea
    Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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  • How to open a VirtualBox (.VDI) Virtual Machine

    - by [email protected]
     How to open a .VDI Virtual MachineSometimes someone share with us one Virtual machine with extension .VDI, after that we can wonder how and what with?Well the answer is... It is a VirtualBox - Virtual Machine. If you have not downloaded it you can do this easily, just follow this post.http://listeningoracle.blogspot.com/2010/04/que-es-virtualbox.htmlorhttp://oracleoforacle.wordpress.com/2010/04/14/ques-es-virtualbox/Ok, Now with VirtualBox Installed open it and proceed with the following:1. Open the Virtual File Manager. 2. Click on Actions ? Add and select the .VDI fileClick "Ok"3.  A new Virtual machine will be displayed, (in this Case, an OEL5 32GB Virtual Machine is available.)4. This step is important. Once you have open the settings, under General option click the advanced settings. Here you must change the default directory to save your Snapshots; my recommendation set it to the same directory where the .Vdi file is. Otherwise you can have the same Virtual Machine and its snapshots in different paths.5. Now Click on System, and proceed to assign the correct memory and define the processors for the Virtual machine. Note: Enable  "Enable IO APIC" if you are planning to assign more than one CPU to the Virtual Machine.6. Associated the storage disk to the Virtual machineThe disk must be selected as IDE Primary Master. 7. Well you can verify the other options, but with these changes you will be able to start the VM. Note: Sometime the VM owner may share some instructions, if so follow his instructions.8. Click Ok and Push Start Button, and enjoy your Virtual Machine

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  • How to open a VirtualBox (.VDI) Virtual Machine

    - by [email protected]
     How to open a .VDI Virtual MachineSometimes someone share with us one Virtual machine with extension .VDI, after that we can wonder how and what with?Well the answer is... It is a VirtualBox - Virtual Machine. If you have not downloaded it you can do this easily, just follow this post.http://listeningoracle.blogspot.com/2010/04/que-es-virtualbox.htmlorhttp://oracleoforacle.wordpress.com/2010/04/14/ques-es-virtualbox/Ok, Now with VirtualBox Installed open it and proceed with the following:1. Open the Virtual File Manager. 2. Click on Actions ? Add and select the .VDI fileClick "Ok"3.  A new Virtual machine will be displayed, (in this Case, an OEL5 32GB Virtual Machine is available.)4. This step is important. Once you have open the settings, under General option click the advanced settings. Here you must change the default directory to save your Snapshots; my recommendation set it to the same directory where the .Vdi file is. Otherwise you can have the same Virtual Machine and its snapshots in different paths.5. Now Click on System, and proceed to assign the correct memory and define the processors for the Virtual machine. Note: Enable  "Enable IO APIC" if you are planning to assign more than one CPU to the Virtual Machine.6. Associated the storage disk to the Virtual machineThe disk must be selected as IDE Primary Master. 7. Well you can verify the other options, but with these changes you will be able to start the VM. Note: Sometime the VM owner may share some instructions, if so follow his instructions.8. Click Ok and Push Start Button, and enjoy your Virtual Machine

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  • ClearType setting ignored in Windows Virtual PC with Windows XP Pro

    - by Yadyn
    I have a VM set up through Windows Virtual PC for Windows XP Pro and I have been completely unable to get ClearType to work. I have turned it on in the Display - Appearance - Effects dialog but it seems like it completely ignores this. All text is still without any anti-aliasing. Even setting it to normal smoothing doesn't work. If I disable Integration Features, it seems to work, but then I lose a lot of nice features. What's weirder, is that the Windows XP Mode installed with Windows Virtual PC (this is separate from my XP Pro VM) works with both ClearType and Integration Features just fine. I turned it on the same way and it works like a charm, no problems. I'm running Windows 7 Professional 64-bit as the host OS and have the latest (to my knowledge) Windows Virtual PC installed. The only funny business I can think of is that I've enabled 24-bit color via the Group Policy setting inside each XP virtual machine (both Pro and the stripped down XP mode copy). This is a fairly well-known trick documented all over the web, but here's a typical post about it.

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  • Tips on setting up a virtual lab for self-learning networking topics

    - by Harry
    I'm trying to self-learn the following topics on Linux (preferably Fedora): Network programming (using sockets API), especially across proxies and firewalls Proxies (of various kinds like transparent, http, socks...), Firewalls (iptables) and 'basic' Linux security SNAT, DNAT Network admininstration power tools: nc, socat (with all its options), ssh, openssl, etc etc. Now, I know that, ideally, it would be best if I had 'enough' number of physical nodes and physical network equipment (routers, switches, etc) for this self-learning exercise. But, obviously, don't have the budget or the physical space, nor want to be wasteful -- especially, when things could perhaps be simulated/emulated in a Linux environment. I have got one personal workstation, which is a single-homed Fedora desktop with 4GB memory, 200+ GB disk, and a 4-core CPU. I may be able to get 3 to 4 additional low-end Fedora workstations. But all of these -- including mine -- will always remain strictly behind our corporate firewall :-( Now, I know I could use VirtualBox-based virtual nodes, but don't know if there are any better alternatives disk- and memory- footprint-wise. Would you be able to give me some tips or suggestions on how to get started setting up this little budget- and space-constrained 'virtual lab' of mine? For example, how would I create virtual routers? Has someone attempted this sort of thing before: namely, creating a virtual network lab behind a corporate firewall for learning/development/testing purposes? I hope my question is not vague or too open-ended. Basically, right now, I don't know how to best leverage the Linux environment and the various 'goodies' it comes with, and buying physical devices only when it is absolutely necessary.

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  • Creating an Apache Virtual Directory, but updating Active Directory DNS

    - by SnoConeGod
    Hello all, I'm just getting started with using the Zend Framework and am following a recommended procedure where I am supposed to create an Apache Virtual Directory for the public-facing portion of a new Zend project. I don't THINK I had any issues creating the Virtual Directory, but my knowledge of the required DNS changes is rather lacking. The dev server I'm using is on a Microsoft Windows Active Directory domain, so I've added A records for both the server name and the subdomain. Still, trying to browse to the site from a Windows 7 PC isn't working properly. What am I missing? What's the proper set of steps for getting an Apache-served subdomain to appear properly in a peer computer's web browser? Details below: server: Debian command-line only, freshly installed today with Zend Server CE LAMP stack server name: ZENDEV subdomain: SQUARE.ZENDEV AD Domain functional level: 2008 mixed (run by a mishmash of 03 and 08 servers) attempting to visit the sites: http://square.zendev and http://square.zendev.domain.local (name of domain redacted, but using the local (not com) suffix) Apache Virtual Directory added to httpd.conf: NameVirtualHost *:80 <VirtualHost *:80> DocumentRoot "/var/www/square/public" ServerName square.localhost </VirtualHost> Is this only a problem with DNS? Or with DNS and my Virtual Directory? Thanks! John

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  • Multimaster Keepalived Configuration (Virtual IP with Load Balancing)

    - by Rad Akefirad
    Here are requirements: 1. High Availability 2. Load Balancing First configuration 1. Two linux servers have been configured with one static IP for each: 10.17.243.11, 10.17.243.12 2. Keepalived has been installed and configured with one VRRP instance to provide one virtual IP (10.17.243.10 as VIP, 10.17.243.11 as master and 10.17.243.12 as backup). 3. Everything works fine. The VIP is assigned to the master server (10.17.243.11) as long as it is up and running. As soon as it goes down, the VIP will be assigned to the backup server (10.17.243.12). 4. The problem here is all communication goes to the master server. Second configuration 1. I found active-active configuration for Keepalived which is possible by defining more than one VRRP instance. So that both server have two IPs (real 10.17.243.11 and virtual 10.17.243.10 for server #1 and real 10.17.243.12 and virtual 10.17.243.20 for server #2. 2. Everything works fine. we have two VIPs which are accessible (HA). But all communication coming to each IP still goes to one single machine (either server #1 or #2 depending on the IP). However I found some tricks on the DNS to overcome this limitation. But it's not acceptable in our case. Question: Is there any way to have one virtual IP which is assigned to both servers? By that I mean both servers are handling some part of workload (like the thing we do in web server load balancing)? By using either keepalived or some other tools? Thanks in advance.

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  • NAT via iptables and virtual interface

    - by Alex
    I'm trying to implement the following scenario: One VM-host, multiple guest VMs, each one gets its own IP-address (and domain). Our server has only one physical interface, so the intended use is to add virtual interfaces on eth0. To complicate our situation the provider uses port-security on their switches, so I can't run the guest interfaces in bridged mode, because then the switch detects a "spoofed" MAC-address and kills the interface (permanently, forcing me to call the support, which I'm sure will get them a little bit angry the third time ;) ). My first guess was to use iptables and NAT to forward all packages from one virtual interface to another one, but iptables doesn't seem to like virtual interfaces (at least I can't get it to work properly). So my second guess is to use the source IP of the packages to the public interface. Let's assume libvirt creates a virbr0-network with 192.168.100.0/24 and the guest uses 192.168.100.2 as IP-address. This is what I tried to use: iptables -t nat -I PREROUTING --src public_ip_on_eth0:0 -p tcp --dport 80 -j DNAT --to-destination 192.168.100.2:80 That doesn't give me the intended results either (accessing the server times out). Is there a way to do what I'm trying to do, or even to route all traffic to a certain IP on a virtual interface to the VM's device?

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  • Microphone not working in Windows Virtual PC (on Windows 7)

    - by Clay Nichols
    I"m using Windows Virtual PC on Windows 7 (host) running Windows XP (as the Guest O/S) I'm trying to get the Microphone working. When I Enable Integration Features: Microphone does not work When I run the Sound Recorder, the record button is disabled. If I look at Sound settings, there are no options for the Mic (it's all disabled "grayed out"). Speakers work Copy & Paste works When I Disable Integration Features: Microphone and speakers work Copy and Paste does not (as expected) Drag'n Drop copying does not work in either situation. What I've Tried Verified that the Windows XP Mode Virtual PC guest also has the same symptoms (Mic doesn't work) and audio out (speakers) do work. I"m going to try (but have little hope) to: -Uninstall and Reinstall the Integration addin for Virtual PC

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  • How to increase virtual hard drive space

    - by Chris
    I have a Microsoft Virutal PC hard drive (.vhd format) that's maxed out it's 16 gig hard drive space. What would be the best way to increase this diskspace? Booting into the machine (windows xp professional) and using the disk management snap in, I can see that the virtual drive has approximately 40 more unused gigs of space. Trying to use diskpart, I find out that Windows XP can't extend the boot partition. So I'm at an empass, any suggestions on how to increase the partion or to increase the actual virtual hard drive would be great. Note: The virtual hard drive is running on Windows 7 using XP mode.

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  • linux ftp server with virtual users

    - by kjertil
    i know there are already similar questions for this matter but the answers doesn't really make much sense to anyone who is not really technically comfortable in Linux. I've already tried articles like these for example: http://howto.gumph.org/content/setup-virtual-users-and-directories-in-vsftpd/ with the result of accidently breaking the whole system. The problem is that, while there are several technical possibilities to set up virtual users with a FTP server, it is not as easy as managing for instance a Filezilla server on Windows. I've seen some Web based GUI's but most of them seems to be out of date. The different flavours of Linux and the large amount of different popular FTP servers also seems to make the matter more complicated. I guess my question is, is there a way, to set up virtual FTP users on Linux without the hastle of having to manually edit PAM, MYSQL and config files?

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  • Duplicate Name Exists error from virtual PC with NAT network configuration

    - by Phred
    Whenever I change the network configuration to NAT for a virtual machine running under Virtual PC 2007, I get "A duplicate name exists on the network." error. There is no other machine on my network with this name and running the VM in any other network configuration doesn't cause this error. This seems to be a common problem with Virtual PC 2007 based on a google search but no-one seems to have a solution to it. So far, I've discovered that turning off NETBIOS over TCP causes the problem to go away but I need to join this VM to a domain and you can't do that if NETBIOS over TCP is turned off.

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  • Cannot get Virtual PC to install on my machine

    - by Brandon
    I'm not sure what I'm doing wrong. I ran the tool to check that hardware virtualization is enabled, and it is (i7-2600). I ran the proper version of the Virtual PC download (Windows 7 Professional x64) and I can see the Windows Virtual PC (KB958559) update in my installed updates list. The .msu file runs fine without errors, but even after multiple reboots I can't actually find a trace of Virtual PC anywhere. There is nothing in program files, the start menu, or system32. Am I missing a step?

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  • How to use more than 3 virtual disks in Linux using CentOS and XenServer

    - by 010110110101
    I've attached 5 virtual disks to a Virtual Machine in Citrix XenServer. The VM has the xs-tools installed. Initially it said that it couldn't add so many disks. After I installed the xs-tools, it let me add all the disks. But /dev doesn't show all the disks. It shows these: /dev/xvda /dev/xvdb /dev/xvdc /dev/cdrom Perhaps it is bound by the limits of an IDE bus? (3 disks + CD-ROM) If so, how does one change the VM to use SCSI? Edit: According to the documentation: 2.6.3. VM Block Devices In the PV Linux case, block devices are passed through as PV devices. XenServer does not attempt to emulate SCSI or IDE, but instead provides a more suitable interface in the virtual environment in the form of xvd* devices. It is also possible to get an sd* device using the same mechanism, where the PV driver inside the VM takes over the SCSI device namespace. This is not desirable so it is best to use xvd* where possible for PV guests (this is the default for Debian and RHEL). For Windows or other fully virtualized guests, XenServer emulates an IDE bus in the form of an hd* device. When using Windows, installing the Citrix Tools for Virtual Machines installs a special PV driver that works in a similar way to Linux, except in the fully virtualized environment. Still, with 5 virtual disks attached, I don't see the other xvd devices. Edit #2: (attached requested info) Host Machine: XenServer 6.1 Linux version 2.6.32.43-0.4.1.xs1.6.10.777.170770xen (geeko@buildhost) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-51)) #1 SMP Wed Apr 17 05:52:03 EDT 2013 Guest Machine: CentOS release 6.4 (Final) Linux version 2.6.32-358.6.2.el6.x86_64 ([email protected]) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-3) (GCC) ) #1 SMP Thu May 16 20:59:36 UTC 2013 Output of 'fdisk -l' on Guest Machine: Note, the disk beyond the first 3 attached are not displaying -- there should be 4 100GB disks. (There are a total of 5 disks displayed in XenCenter -- 16GB, 100GB, 100GB, 100GB, 100GB) Disk /dev/xvdb: 107.4 GB, 107374182400 bytes 255 heads, 63 sectors/track, 13054 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xfb6c95b9 Device Boot Start End Blocks Id System /dev/xvdb1 1 13054 104856223+ 83 Linux Disk /dev/xvda: 17.2 GB, 17179869184 bytes 255 heads, 63 sectors/track, 2088 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000e5f41 Device Boot Start End Blocks Id System /dev/xvda1 * 1 64 512000 83 Linux Partition 1 does not end on cylinder boundary. /dev/xvda2 64 2089 16264192 8e Linux LVM Disk /dev/xvdc: 107.4 GB, 107374182400 bytes 255 heads, 63 sectors/track, 13054 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xed249ced Device Boot Start End Blocks Id System /dev/xvdc1 1 13054 104856223+ 83 Linux Disk /dev/mapper/vg_blue-lv_root: 14.6 GB, 14571012096 bytes 255 heads, 63 sectors/track, 1771 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/mapper/vg_blue-lv_swap: 2080 MB, 2080374784 bytes 255 heads, 63 sectors/track, 252 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 I see that the Linux versions say SMP. The Guest VM doesn't say "xen" in the name. However, I have already run yum install kernel-xen. Could be a clue?

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  • Best Practices vs Reality

    - by RonHill
    On a scale depicting how closely best practices are followed, with "always" on one end and "never" on the other, my current company falls uncomfortably close to the latter. Just a couple trivial examples: We have no code review process There is very little documentation despite a very large code base (and some of it is blatantly incorrect/misleading) Untested/buggy/uncompilable code is frequently checked in to source control It is comically complicated to create a debuggable build for some of our components because of its underlying architecture. Unhandled exceptions are not uncommon in our releases Empty Catch{ } blocks are everywhere. Now, with the understanding that it's neither practical nor realistic to follow ALL best practices ALL the time, my question is this: How closely have commonly accepted best practices been followed at the companies you've worked for? I'm kind of a noob--this is only the second company I've worked for--so I'm not sure if I'm just more of an anal retentive coder or if I've just ended up at mediocre companies. My guess (hope?) is the latter, but a coworker with way more experience than me says every company he's ever worked for is like this. Given the obvious benefits of following most best practices most of the time, I find it hard to believe it's like this everywhere. Am I wrong?

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  • Virtual PC on Windows 7 - Hardware-assisted virtualization is disabled

    - by DLux
    I am running a Lenovo Thinkpad T61 with an Intel Core 2 Duo T7300 processor. When I run Virtual PC in Windows 7, I get the following error: Unable to start Windows Virtual PC because hardware-assisted virtualization is disabled. When running the Hardware-Assisted Virtualization Detection Tool from Microsoft says: Hardware-assited virtualization is not enabled on this computer. Now, in the BIOS, I do have virtualization enabled and according to Intel this processor supports Intel-VT. What am I missing here?

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  • IIS6 Virtual Directory 500 Error on Remote Share

    - by David
    We have our servers at the server farm in a domain. Let's call it LIVE. Our developer computers live in a completely separate corporate domain, miles and miles away. Let's call it CORP. We have a large central storage unit (unix) that houses images and other media needed by many webservers in the server farm. The IIS application pools run as (let's say) LIVE\MediaUser and use those credentials to connect to a central storage share as a virtual directory, retrieve the images, and serve them as if they were local on each server. The problem is in development. On my development machine. I log in as CORP\MyName. My IIS 6 application pool runs as Network Service. I can't run it as a user from the LIVE domain because my machine isn't (and can not be) joined to that domain. I try to create a virtual directory, point it to the same network directory, click Connect As, uncheck the "Always use the authenticated user's credentials when validating access to the network directory" checkbox so that I can enter the login info, enter the credentails for LIVE\MediaUser, click OK, verify the password, etc. This doesn't work. I get "HTTP Error 500 - Internal server error" from IIS. The IIS log file reports sc-status = 500, sc-substatus = 16, and sc-win32-status = 1326. The documentation says this means "UNC authorization credentials are incorrect" and the Win32 status means "Logon failure: unknown user name or bad password." This would be all and good if it were anywhere close to accurate. I double- and trouble-checked it. Tried multiple known good logins. The IIS manager allows me to view the file tree in its window, it's only the browser that kicks me out. I even tried going to the virtual directory's Directory Security tab, and under Authentication and Access Control, I tried using the same LIVE domain username for the anonymous access credential. No luck. I'm not trying to run any ASP, ASP.NET, or other dynamic anything out of the virtual directory. I just want IIS to be able to load static images, css, and js files. If anyone has some bright ideas I would be most appreciative!

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  • virtual appliance resources

    - by user11457
    I'm fairly new to appliances but have become a big fan of virtualization. Are there any other resources where I can find and download virtual appliances outside of vmware's website? Or do I just need to scour the web looking them? I'm sure there is a central site that lists all the virtual appliances available, if there isn't I'm going to write one.

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