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  • Can I install two Ubuntu versions on the same machine?

    - by Abh
    Hello, I have Ubuntu 10.10 32 bit already installed on my machine..I am using MongoDB and it does not work properly with 32 bit machine. So I want to install 64 bit Ubuntu 10.10 on my system on another partition (so that I can have both 32 bit and 64 bit versions). Is it okay to install both 32 bit and 64 bit? I mean will it give any problems? On which partition should I install the 64 bit version? My partitions are as follows: Filesystem Size Used Avail Use% Mounted on /dev/sda1 37G 11G 25G 30% / none 1.4G 260K 1.4G 1% /dev none 1.4G 776K 1.4G 1% /dev/shm none 1.4G 244K 1.4G 1% /var/run none 1.4G 0 1.4G 0% /var/lock /dev/sda6 129G 73G 50G 60% /home /dev/sda7 127G 76G 45G 64% /vol Waiting for your replies.

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  • Linux: page faults and network filesystems

    - by Alex B
    If a Linux system runs out of physical memory, does it drop inactive executable code pages? I assume the answer is yes, since there is no reason to keep them in swap, so they are simply discarded and re-loaded if necessary (as far as I know, that's what FreeBSD does). If the above is true for Linux, my question is, how does it handle executables run from network filesystems (e.g. NFS)? Does it go and fetch executable pages over the network if there is a page fault?

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  • How do you differentiate between "box," "machine," "computer" and whatever else?

    - by Corey
    There seems to be a few terms for referring to a computer, especially in the tech world. Different terms seem to be used based on technical expertise. When talking with people with some technical knowledge, I'll refer to it as a machine. When talking to non-technical people (family, friends) I'll call it a computer. On the rare occasion I'm talking about servers, I might call it a box, but even then I'll probably still call it a machine. Is that just me, or do there exist rules already for what to call a computer?

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  • Why does Java's invokevirtual need to resolve the called method's compile-time class?

    - by Chris
    Consider this simple Java class: class MyClass { public void bar(MyClass c) { c.foo(); } } I want to discuss what happens on the line c.foo(). At the bytecode level, the meat of c.foo() will be the invokevirtual opcode, and, according to the documentation for invokevirtual, more or less the following will happen: Look up the foo method defined in compile-time class MyClass. (This involves first resolving MyClass.) Do some checks, including: Verify that c is not an initialization method, and verify that calling MyClass.foo wouldn't violate any protected modifiers. Figure out which method to actually call. In particular, look up c's runtime type. If that type has foo(), call that method and return. If not, look up c's runtime type's superclass; if that type has foo, call that method and return. If not, look up c's runtime type's superclass's superclass; if that type has foo, call that method and return. Etc.. If no suitable method can be found, then error. Step #3 alone seems adequate for figuring out which method to call and verifying that said method has the correct argument/return types. So my question is why step #1 gets performed in the first place. Possible answers seem to be: You don't have enough information to perform step #3 until step #1 is complete. (This seems implausible at first glance, so please explain.) The linking or access modifier checks done in #1 and #2 are essential to prevent certain bad things from happening, and those checks must be performed based on the compile-time type, rather than the run-time type hierarchy. (Please explain.)

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  • Can you force a crash if a write occurs to a given memory location with finer than page granularity?

    - by Joseph Garvin
    I'm writing a program that for performance reasons uses shared memory (alternatives have been evaluated, and they are not fast enough for my task, so suggestions to not use it will be downvoted). In the shared memory region I am writing many structs of a fixed size. There is one program responsible for writing the structs into shared memory, and many clients that read from it. However, there is one member of each struct that clients need to write to (a reference count, which they will update atomically). All of the other members should be read only to the clients. Because clients need to change that one member, they can't map the shared memory region as read only. But they shouldn't be tinkering with the other members either, and since these programs are written in C++, memory corruption is possible. Ideally, it should be as difficult as possible for one client to crash another. I'm only worried about buggy clients, not malicious ones, so imperfect solutions are allowed. I can try to stop clients from overwriting by declaring the members in the header they use as const, but that won't prevent memory corruption (buffer overflows, bad casts, etc.) from overwriting. I can insert canaries, but then I have to constantly pay the cost of checking them. Instead of storing the reference count member directly, I could store a pointer to the actual data in a separate mapped write only page, while keeping the structs in read only mapped pages. This will work, the OS will force my application to crash if I try to write to the pointed to data, but indirect storage can be undesirable when trying to write lock free algorithms, because needing to follow another level of indirection can change whether something can be done atomically. Is there any way to mark smaller areas of memory such that writing them will cause your app to blow up? Some platforms have hardware watchpoints, and maybe I could activate one of those with inline assembly, but I'd be limited to only 4 at a time on 32-bit x86 and each one could only cover part of the struct because they're limited to 4 bytes. It'd also make my program painful to debug ;)

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  • How does memory protection in SASOS works?

    - by chris
    I'd like to know how it works - whether it checks if process can read/write/execute memory on every access, or it does it only once? But when it does it only once, and all processes are in a single address space, how are these other hostile processes are prevented from accessing memory from not their's areas?

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  • Oracle makes Virtualized Java Applications Practical. Announces Brand New Products

    - by blake.connell
    New Oracle Virtual Assembly Builder and Oracle WebLogic Suite Virtualization Option make running Java applications in a virtual environments easy and practical. • Oracle Virtual Assembly Builder is a new product designed to help organizations quickly and easily deploy multi-tier enterprise applications in virtualized environments. It enables administrators to quickly configure and provision these applications. • Oracle WebLogic Suite Virtualization Option delivers Oracle WebLogic Server on Oracle JRockit Virtual Edition delivering 'near-native' performance and increased server density. • Oracle WebLogic Server on Oracle JRockit Virtual Edition runs directly on Oracle VM without a guest operating system, a unique capability resulting in better performance and more application server runtime per system. Oracle WebLogic Suite Virtualization Option and Oracle Virtual Assembly Builder can drive operational efficiency and agility. Customers can dynamically scale up/down the underlying software infrastructure and applications with ease through software automation. Register for a live webinar with Oracle product experts Read the press release For more product information: Oracle Virtual Assembly Builder Oracle WebLogic Suite Virtualization Option

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  • Self-describing file format for gigapixel images?

    - by Adam Goode
    In medical imaging, there appears to be two ways of storing huge gigapixel images: Use lots of JPEG images (either packed into files or individually) and cook up some bizarre index format to describe what goes where. Tack on some metadata in some other format. Use TIFF's tile and multi-image support to cleanly store the images as a single file, and provide downsampled versions for zooming speed. Then abuse various TIFF tags to store metadata in non-standard ways. Also, store tiles with overlapping boundaries that must be individually translated later. In both cases, the reader must understand the format well enough to understand how to draw things and read the metadata. Is there a better way to store these images? Is TIFF (or BigTIFF) still the right format for this? Does XMP solve the problem of metadata? The main issues are: Storing images in a way that allows for rapid random access (tiling) Storing downsampled images for rapid zooming (pyramid) Handling cases where tiles are overlapping or sparse (scanners often work by moving a camera over a slide in 2D and capturing only where there is something to image) Storing important metadata, including associated images like a slide's label and thumbnail Support for lossy storage What kind of (hopefully non-proprietary) formats do people use to store large aerial photographs or maps? These images have similar properties.

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  • How do I prevent having to log in on 3 separate prompts every time I start my machine?

    - by JC
    Ubuntu 11.04 Natty Narwhal, Ubuntu Classic desktop Each time I start my machine, I have to log in 3 times. I spent a week in IRCFreenode#ubuntu and got nothing but condescension. I've searched on the official Ubuntu fora for similar problems, tried every recommendation, and still get 3 login screens. As a workaround, I have reset login such that I get a login screen at startup, which I'd prefer not to get since this machine is accessible by no one but me, physically. I have gone into System Preferences Passwords and Encryption Keys, set first 'Passwords: default' to 'Default' and unlocked it, and unlocked the 'Passwords: login' key, too. Next, since that changed nothing, I set 'Passwords: login' to 'Default', and checked to make sure it was still unlocked. Again, no change, still get 3 login prompts at startup. I've checked twice to insure that I am the owner of the files; I am. At the suggestion of several people in #ubuntu, I've deleted first one, then the other password key in 'Passwords and Encryption Keys'. Still get 3 login prompts. I changed from the Unity desktop to Ubuntu Classic. While that didn't fix the above problem, it is a much more elegant desktop than Unity, and I'll keep it. From what I've read, this seems to be a Seahorse issue, but beyond that, no one seems to have a solution that works. I'm lost. This shouldn't be this difficult or annoying. I'm trying to help our local Old Time music collective get their machines switched over to Ubuntu in order to save them some money which they can use to promote their DRM-free music. But from what I've seen of Ubuntu so far on my own machine, I can't really recommend that they make this switch. I hope to be proved wrong on that point. But as it stands, if I was out of town or out of country and they ran into a problem, they'd have no way of fixing it as they're all less experienced than even I am. I'm not trying to cast aspersions on Ubuntu or Linux, but it seems pretty clear that KNOWLEDGEABLE, HELPFUL support for Ubuntu is lacking barring any desire on the problem-experiencing-user's part to avoid condescension. Having worked with, and run, several non-profits over the past 20 years, I know that getting volunteers to act professionally can be like herding cats. But an organization's reputation can be denigrated by sarcastic behaviors on the part of those who serve, effectively, as its public face. Thank you all for your help and support. Now...does anyone have a solution to my problem?

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  • Why isn't there a python compiler to native machine code?

    - by user2986898
    As I understand, the cause of the speed difference between compiled languages and python is, that the first compiles code all way to the native machine's code, whereas python compiles to python bytecode, to be interpreted by the PVM. I see that this way python codes can be used on multiple operation system (at least in most cases), however I do not understand, why is not there an additional (and optional) compiler for python, which compiles the same way as traditional compilers. This would leave to the programmer to chose, which is more important to them; multiplatform executability or performance on native machine. In general; why are not there any languages which could be behave both as compiled and interpreted?

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  • How to get client machine ip address in custom realm? [on hold]

    - by Sumit
    I want to get client machine ip address in my custom Realm when client attempt to login basically here is detail requirement of project User having role 'Admin' can add new users and assign multiple roles and permission ,and at the same time specify list of ip address and countries to restrict them to access website. All these information i am storing in database. So basically till now i am using shiro default 'authc' filter but now i want ip address of client machine and get country from where request is coming and check it against database and then and then only allow access to website. Any help..? Thanks and regards

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  • How to connect to a WCF service using IP of the host machine where the service is hosted?

    - by Kumar
    I have a secured WCF service (https://<MachineName>:sslport/services) self hosted in a machine. Different instances of same service are deployed in differnt machines. From a client app, I am able to connect to theses services through code, i.e. using ChannelFactory() with the same endpoint address. But if I try to access the service using the endpoint address as https://<ipAddress>:sslport/services replacing machines name with machine IP address, I am getting some error stating "could not establish trust relationship". I know this is an error caused by SSL certificate that it could not establish a trust relationship. Are there any settings or any possibilities to make this work?

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  • How can I get read-ahead bytes?

    - by Bruno Martinez
    Operating systems read from disk more than what a program actually requests, because a program is likely to need nearby information in the future. In my application, when I fetch an item from disk, I would like to show an interval of information around the element. There's a trade off between how much information I request and show, and speed. However, since the OS already reads more than what I requested, accessing these bytes already in memory is free. What API can I use to find out what's in the OS caches? Alternatively, I could use memory mapped files. In that case, the problem reduces to finding out whether a page is swapped to disk or not. Can this be done in any common OS?

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  • Understanding Virtualization

    - by mohit
    Hi, I wana to know about Virtualization in detail. But start from basics, like what is virtualization, with real world examples and scenarios. When ever i search, i got Virtualization technologies, but i want to learn and in fcat know what exactly is virtualization, its types n all..... Please help me in getting practical details of term "Virtualization"

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  • How to reliably measure available memory in Linux?

    - by Alex B
    Linux /proc/meminfo shows a number of memory usage statistics. MemTotal: 4040732 kB MemFree: 23160 kB Buffers: 163340 kB Cached: 3707080 kB SwapCached: 0 kB Active: 1129324 kB Inactive: 2762912 kB There is quite a bit of overlap between them. For example, as far as I understand, there can be active page cache (belongs to "cached" and "active") and inactive page cache ("inactive" + "cached"). What I want to do is to measure "free" memory, but in a way that it includes used pages that are likely to be dropped without a significant impact on overall system's performance. At first, I was inclined to use "free" + "inactive", but Linux's "free" utility uses "free" + "cached" in its "buffer-adjusted" display, so I am curious what a better approach is. When the kernel runs out of memory, what is the priority of pages to drop and what is the more appropriate metric to measure available memory?

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  • Prevent mapping all public members of a class in Fluent NHibernate

    - by alimbada
    I have a class generated from a WSDL that has a bunch of public properties and a public event. I'm extending this class with my own and adding some properties to it. All of my own properties are declared virtual, but the base class properties are not virtual. I'm using Fluent NHibernate's ClassMap to map only the properties from my extended class. How do I prevent (Fluent)NHibernate from trying to persist all the base class's public members? At the moment, I get the following exception when creating the ISessionFactory: NHibernate.InvalidProxyTypeException: The following types may not be used as proxies: Type: method get_<BaseClassProperty should be 'public/protected virtual' or 'protected internal virtual' Type: method set_<BaseClassProperty should be 'public/protected virtual' or 'protected internal virtual' ... Type: method add_<BaseClassEvent should be 'public/protected virtual' or 'protected internal virtual' Type: method remove_<BaseClassEvent should be 'public/protected virtual' or 'protected internal virtual'

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  • How communicate with pty via minicom or screen?

    - by gscott2112
    I am trying to provide an AT/Modem-like interface around some hardware. Follwing this post I have the server setting up a pty using openpty(). Now I can communicate with the server as expected with a client app that open the slave and communicates via read() and write() calls. However I would also like to be able to use either the screen command or minicom to issue commands by hand to the slave. However the server never seems to receive any data when trying to do this. Is there something significant I am missing with this approach?

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  • How do I set up for sharing code (ASP.NET) across multiple domain names?

    - by Scott J.
    I have built a website and now the customer wants to split it between three different domains. What is the best way to do this? This is what I have so far. c:/website1/ points to www.website1.com c:/website1/vd1/ points to www.website2.com c:/website1/vd2/ points to www.website3.com The webhost I'm working with has done it the following way, but now I'm getting a bunch of errors that seems like it's not seeing the App_code folder. Do I need to make a lot of changes? How does this affect the location references?

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  • Why is not there a python compiler to native machine's code?

    - by user2986898
    As I understand, the cause of the speed difference between compiled languages and python is, that the first compiles code all way to the native machine's code, whereas python compiles to python bytecode, to be interpreted by the PVM. I see that this way python codes can be used on multiple operation system (at least in most cases), however I do not understand, why is not there an additional (and optional) compiler for python, which compiles the same way as traditional compilers. This would leave to the programmer to chose, which is more important to them; multiplatform executability or performance on native machine. In general; why are not there any languages which could be behave both as compiled and interpreted?

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  • In what circumstances can large pages produce a speedup ?

    - by timday
    Modern x86 CPUs have the ability to support larger page sizes than the legacy 4K (ie 2MB or 4MB), and there are OS facilities (Linux, Windows) to access this functionality. The Microsoft link above states large pages "increase the efficiency of the translation buffer, which can increase performance for frequently accessed memory". Which isn't very helpful in predicting whether large pages will improve any given situation. I'm interested in concrete, preferably quantified, examples of where moving some program logic (or a whole application) to use huge pages has resulted in some performance improvement. Anyone got any success stories ? There's one particular case I know of myself: using huge pages can dramatically reduce the time needed to fork a large process (presumably as the number of TLB records needing copying is reduced by a factor on the order of 1000). I'm interested in whether huge pages can also benefit more mundane applications though.

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  • How to shrink Windows 7 XP Mode VHD files?

    - by A_M
    I'm trying to shrink a Windows 7 XP Mode VHD file with VhdResizer with little success. When I select my VHD file, it says "VhdExpand only supports fixed and dynamic VHD files". My XP Mode VHDs are dynamic files. Does anyone have any idea why it is failing? Failing that, does anyone have a process that I can use to shrink my XP mode VHD files on Windows 7 (64 bit)?

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