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Questions tagged [virtual-machines]

A virtual machine (VM) is a completely isolated guest operating system installation within a normal host operating system. It is a software implementation of a machine (i.e. a computer) that executes programs like a physical machine.

80
votes
6answers
81k views

What range of MAC addresses can I safely use for my virtual machines?

I want to assign my virtual machines MAC addresses so that I can configure DHCP reservations for them so that they always get the same IP address regardless of which host hypervisor they are running ...
74
votes
2answers
25k views

Why do we use a OS Base Image with Docker if containers have no Guest OS?

I've just started to study Docker and there's something that's being quite confusing for me. As I've read on Docker's website a container is different from a virtual machine. As I understood a ...
66
votes
3answers
11k views

Is a VM with 2 CPUs really faster than one with 4 CPUs?

Our IT created a VM with 2 CPUs allocated rather than the 4 I requested. Their reason is that the VM performs better with 2 CPUs rather than 4 (according to them). The rationale is that the VM ...
65
votes
2answers
103k views

Is it possible to make Nginx listen to different ports?

I created one Nginx with one Linux Azure VM, is it possible to make nginx listen to different ports so that when I change the port number, the content would be different. I found there would be a ...
58
votes
9answers
156k views

Creating a virtual machine in VirtualBox from a physical one

Is there any way to create a virtual machine that you can use in VirtualBox from a physical installation that you have? For instance, if I have Windows XP installed on a physical computer and want to ...
53
votes
14answers
210k views

How do I know if I'm working on a Virtual Machine or not?

Is there a way to know if the Windows machine I'm working on is virtual or physical? (I'm connecting with RDP to the machine. If it's a virtual machine it is working and handled by VMWare).
30
votes
12answers
72k views

Is it possible to setup a virtual machine inside another virtual machine

I have been playing with virtual machines latley, and wondered if I could run a virtual machine inside a virtual machine? Is it possible? Is it practical?
27
votes
4answers
33k views

Why VM snapshots are affecting performance?

I read in one of the VMware KB articles that snapshots will directly affect VM performance. But my team keeps asking me how snapshots can affect performance. I would like to give them solid reason ...
26
votes
4answers
807 views

Will virtualizing a server mean another OS layer to patch and update, more work and greater risk?

I've done a search and have not found anything addressing issues regarding patching and system updates. I've got guidelines that say servers need to have necessary patches. If I have a VM host then ...
25
votes
5answers
972 views

Is there a reason to give a VM a round base-2 amount (2048MB, 4096MB, etc) of memory?

The title pretty much says it all, is there any advantage to giving a VM 2048MB of memory instead of rounding to base-10 and doing 2000MB?
24
votes
10answers
54k views

Running 100 virtual machines on a single VMWare host server

I've been using VMWare for many years, running dozens of production servers with very few issues. But I never tried hosting more than 20 VMs on a single physical host. Here is the idea: A stripped ...
23
votes
17answers
3k views

Virtualization Pitfalls/Lessons Learned

What are some pitfalls or lessons learned after converting existing hardware to a virtualized environment? Is there anything you tried to virtualize but will never do again?
22
votes
2answers
15k views

When shall I use linked vs full VM clones?

I've seen documentation for the Full and Linked virtual machine clones, but I can't seem to fully understand when I should use one over another. I see that the full clone creates a copy of the VM, but ...
22
votes
1answer
35k views

KVM and Libvirt - How do I hotplug a new virtio disk?

I am trying to hot-add a file-based disk to a running KVM virtual server. I've created a new disk from scratch using the command dd of=/home/cloud/vps_59/test.img bs=1 seek=5G count=0 and I was ...
21
votes
10answers
32k views

Sync LVM snapshots to backup server

I have a number of Xen virtual machines running on a number of Linux servers. These VMs store their disk images in Linux LVM volumes with device names along the lines of /dev/xenVG/SERVER001OS and so ...
19
votes
5answers
1k views

Can a VMWare Server 2.0 virtual machine be “unvirtualized” to physical hardware?

We have a number of VMWare Server 2.0 virtual machines that were created using VMWare Converter (It copies a physical machine to a virtual machine). If we need to convert the virtual machine back to a ...
18
votes
5answers
1k views

Is there a way to have a virtual machine only have one core yet use three cores on the host machine? [duplicate]

Possible Duplicate: Can a single Virtual Core on a VM use more then 1 physical core? I'm a co-owner of a Minecraft server that is getting rather large each day, but as we get bigger we're running ...
18
votes
9answers
47k views

Hyper-V vs. ESXi vs. XenServer

Can anyone share their experiences (for example, this was great! This failed miserably!) with using the Hyper-V, ESXi, and XenServer virtualization platforms? Cost? Management? features? Handling load ...
18
votes
3answers
16k views

How is memory allocated in ESXi server?

We have an ESXi 4.1 server with 48 GB RAM. For each VM, we are allocating 4GB of memory. Since the server will have 13 virtual machines, my manager thinks this is wrong. I am going to explain to ...
18
votes
4answers
29k views

How to attach a virtual hard disk using VBoxManage?

What is the best method for setting the virtual hard drive (VDI) of the primary controller for an existing virtual machine? Does the syntax change if the VDI is really a child differencing disk of ...
17
votes
5answers
6k views

Defrag in Windows VM?

I've read conflicting advice on this issue so thought I'd ask here. Should I be running a scheduled defrag within my VM?
17
votes
6answers
16k views

How do I get /dev/random to work on an Ubuntu virtual machine?

Apparently, /dev/random is based on hardware interrupts or similar unpredictable aspects of physical hardware. Since virtual machines don't have physical hardware, running cat /dev/random within a ...
17
votes
2answers
4k views

understanding relationship between Qemu and KVM

What is the difference between KVM and Qemu? As I understand, latter is able to provide "user mode emulation" which means that one can run a single executable built for some other architecture like ...
15
votes
1answer
38k views

Why Are There Only 65,535 Ports, and Will We Ever Have More? [closed]

I understand the original reasoning behind having 65,535 ports per IP address: this is the highest number that can be represented by a 16-bit, or 2-byte, number, and it wasn't conceivable that ...
15
votes
15answers
41k views

Web based KVM management for Ubuntu

We've got a single Ubuntu 9.10 root server on which we want to run multiple KVM virtual machines. To administer these virtual machines I'd like a web based KVM management tool, but I don't know which ...
15
votes
2answers
16k views

Running containers inside a virtual machine?

It is my understanding that containers are much more lightweight than VMs because they do not virtualize the hardware but instead just isolate the software running in them from software running in ...
15
votes
2answers
23k views

Renaming an Azure VM

I am looking to rename an Azure VM. I have copied a VM from one subscription to another using this guide: http://blogs.msdn.com/b/microsoft_press/archive/2014/01/29/from-the-mvps-copying-a-virtual-...
14
votes
5answers
10k views

So really, what is the overhead of virtualization and when should I be concerned?

I'm searching for good rules of thumb to understand when NOT to virtualize a machine. For example, I know that a fully CPU-bound process with near 100% utilization is probably not a good idea to ...
14
votes
2answers
321 views

How to get free space from mounted drive Redhat 7

In our VM infrastructure, we have clustered hosts going to a SAN. What i am trying to figure out is how much "white space" is left over when deleting files within our Redhat servers. On our Windows ...
13
votes
5answers
2k views

Renting a dedicated, but getting a VPS. How to detect? [duplicate]

When renting a dedicated server, how can one be certain than he/she is not getting a VPS or some other virtual machine variant instead of a true dedicated hardware box? Which checks can be run (...
13
votes
8answers
814 views

What is this server doing?

I have a bunch of linux virtual servers left over from a previous IT department. They have names like 'magic' or 'stuff'. I'm not quite sure what they're doing...or if I need them... How would you ...
13
votes
3answers
15k views

MSTSC: Black Areas on Remote Desktop

I'm connecting from Windows Server 2012 R2 to Hyper-V virtual machine running Windows 8.1 via RDP (mstsc.exe). The VM is hosted on the same machine from which I'm connecting. Everything was fine until ...
13
votes
4answers
14k views

Backing up qcow2 kvm guests

I can't find any good info on backing up qcow2 kvm guests. I'm not really interested in the guests running state, only the file system. This question suggests using savevm but that creates a snapshot ...
13
votes
3answers
6k views

Vagrant shared folder and file change events

I have ubuntu virtual machine that I'm accessing through Vagrant. On my host (Mac OSX), there is a folder with couple of files, that I share to virtual machine. In that virtual machine, I want to use ...
13
votes
2answers
9k views

Entropy on virtual machines

As you might know that it's not as easy to generate entropy on a virtual machine as on a "normal" pc. Generating a gpg-key on a virtual machine can take a while, even with the correct tools. There ...
13
votes
3answers
35k views

Cloning Virtual Machine On Azure, keeping existing

There doesn't seem to be a straight answer online about this. I have an existing Virtual Machine on Azure and I want to clone it to another region in case my existing server goes down. It needs to be ...
12
votes
11answers
10k views

Any way to run Linux as a Virtual Machine on top of Windows so can have best of both worlds?

Since Linux has a lot of useful tools, while Windows has a lot of apps (like Chrome), instead of buying another machine to run Linux, is there a way to run it as a Virtual Machine on the PC? The ...
12
votes
4answers
9k views

Can a virtual machine (VM) “hack” another VM running on the same physical machine?

Questions: if a VM is corrupted (hacked), what do I risk on others VMs running on the same physical machine? What kind of security issues is there between VMs running on the same physical host? Is ...
12
votes
2answers
3k views

Windows Server 2008 R2 64-bit memory leak

I´m having trouble in one of my office servers. It´s a virtualized Windows 2008 R2 Server with 6GB RAM memory. It only has Microsoft SQL Server (memory assigned maximum = 3GB), and just a software ...
12
votes
4answers
4k views

What happens when a physical machine fails in a virtual environment? [closed]

I'm getting started with virtualization so bear with me. In virtual environments applications run in a hypervisor's layer. So a single physical machine could have many virtual machines on it running ...
12
votes
6answers
35k views

Can I run 64-bit VM guests on a 32-bit host?

Can I run 64-bit VM guests on a 32-bit host? If I have a physical PC with 32 bit can I launch a VM that is 64 bit? What virtual machine software (Virtual PC or VirtualBox or other) would allow this? ...
12
votes
1answer
1k views

KVM Host with 88 physical cores uses only 14 on 64 core Guest

I do have a server with 2 CPUs (22 Cores each plus HT). I created a KVM Guest with 64 allocated cores. When I run a compilation task the virtual machine shows all 64 cores at 100% (at moderate Disk I/...
12
votes
3answers
15k views

Why can't I ssh into (or even ping) my Ubuntu VM from the Mac OS X host?

I'm running Ubuntu 8.04 as a virtual machine using VMware Fusion 3.0 on Mac OS X 10.5.8. I want to be able to ssh into my VM from the Mac OS X host (so I can use MacFUSE and SSHFS to mount the VM's ...
11
votes
6answers
57k views

mount.nfs: access denied by server while mounting

On my Ubuntu system, I have this line in /etc/fstab: myserver:/home/me /mnt/me nfs rsize=8192,wsize=8192,timeo=14,intr When I do sudo mount -a I get: mount.nfs: access denied by server while ...
11
votes
3answers
11k views

PING icmp open socket: Operation not permitted in vserver

I am running a vserver environment with several virtual machines. A single VM has the following problem: $ ping 8.8.8.8 ping: icmp open socket: Operation not permitted $ ls -l $(which ping) -rwsr-xr-...
11
votes
2answers
3k views

Hot-remove memory in a Linux virtual machine

Linux supports hot-adding memory when running as a VM guest, in VMware for example. (Sometimes you need to manually inform the guest OS.) Is there a safe way to do the inverse operation — reducing ...
11
votes
2answers
42k views

Running Mac OS X on Hyper-V

I have my workstation setup with a Windows Server 2008 running Hyper-V. Now I really want to install OS X for testing purposes. Have anyone had any success running Mac OS X in an Hyper-V environment? ...
10
votes
6answers
14k views

How to setup /etc/issues to show the IP address for eth0

I've got a couple of linux virtual machines with bridged interfaces, and I'd like the IP address of the machine to show up after the machine boot (in the login, where it usually shows the release and ...
10
votes
3answers
404 views

Adding VM's to Domain

I am trying to configure SP farm, in Azure, following steps mention in this article - https://technet.microsoft.com/en-us/library/mt723354(v=office.16).aspx But after creating Sql VM('sqlVM' ), I am ...
10
votes
4answers
23k views

Is it dangerous to change the value of /proc/sys/net/ipv4/tcp_tw_reuse?

We have a couple of production systems that were recently converted into virtual machines. There is an application of ours that frequently accesses a MySQL database, and for each query it creates a ...