From Fedora Project Wiki
by Kevin Fenzi (irc: nirik)
IRC Log
| @nirik | Hello everyone. I'm Kevin Fenzi and I will be talking about libvirt | 18:59 |
|---|---|---|
| @nirik | right here Acedip. ;) | 19:00 |
| Acedip | hello.. :) | 19:00 |
| pluvo | hi! | 19:00 |
| homerofutoi | hello | 19:00 |
| Acedip | i dint know you are the one :D | 19:00 |
| openpercept_ | hi nirik | 19:00 |
| * jayson_r waves hi! | 19:00 | |
| @nirik | I'd like to note that I am a user of libvirt, I don't maintain or develop it. :) All that is needed to teach is a understanding of something and a desire to teach it. ;) | 19:00 |
| @nirik | so, lets go ahead and get started then. | 19:01 |
| @nirik | First of all: what is libvirt? libvirt is a frontend management framework for virtualization. | 19:01 |
| @nirik | It allows you to use a common set of commands and configuration over a range of backend virt tech. | 19:01 |
| @nirik | libvirt supports (that I know of): qemu, kvm, virtualbox, containers, xen and likely other backends. | 19:02 |
| @nirik | How many people here have run virtual machines before? And what did you use? | 19:02 |
| * subfusc used qemu | 19:02 | |
| homerofutoi | me, i've use virtualbox | 19:03 |
| * Acedip used vbox | 19:03 | |
| openpercept_ | used qemu, vmware, virtualbox | 19:03 |
| @nirik | cool. | 19:03 |
| @nirik | I use kvm here, so that is what I know best... but much of this will apply to any of the backends libvirt supports. | 19:03 |
| * jayson_r uses kvm in Fedora, VirtualBox & Xen on Centos, and Citrix XenServer | 19:03 | |
| pluvo | vmware and later virtualbox | 19:03 |
| * herlo has used kvm, xen, etc... | 19:03 | |
| @nirik | kvm and qemu are available in fedora. | 19:03 |
| @nirik | You can install libvirt (and qemu/kvm) via 'yum groupinstall "Virtualization"' | 19:04 |
| @nirik | libvirtd then runs as a regular service. This daemon looks at your config and takes care of setting up networks, talking to the various backends and starting/stopping virtuals, etc. | 19:05 |
| @nirik | by default, libvirtd in fedora will start up with a private virtual network for your guests and use qemu or kvm if your processor supports it. | 19:05 |
| * nirik will point out http://fedoraproject.org/wiki/Getting_started_with_virtualization has some good startup tips as well. | 19:06 | |
| @nirik | once libvirtd is running on your system you can connect to it via command line tools or virt-manager (a gui) | 19:07 |
| @nirik | note that you don't need to be on the same machine your libvirtd is running on. You can use ssh transport to connect to it from any machine you like. | 19:07 |
| @nirik | lets take a look at virt-manager first. If anyone wants to look around, you can run the above yum command and you should then be able to run 'virt-manager' to start the gui | 19:08 |
| @nirik | for those of you not able to, you can look at scrreenshots at http://virt-manager.et.redhat.com/screenshots.html | 19:08 |
| @nirik | so, this gui is pretty easy to deal with. From here you can connect to any machine running libvirtd and manage it. | 19:09 |
| @nirik | you can setup new guests, stop or start guests, take snapshots, view a console or serial console and add/remove hardware | 19:09 |
| * subfusc wished to ask stupid question: This is the client? | 19:09 | |
| @nirik | virt-viewer is just a management tool that connects to any libvirtd instance... | 19:10 |
| @nirik | does that answer the question? or what do you mean by client? | 19:10 |
| subfusc | ah k, thanks. It answers it. If libvrtd is the backend or service, virt-viewer is in my world a client (admin clent thou) | 19:11 |
| @nirik | yeah | 19:11 |
| @nirik | ok, so if we want to create a new guest, you can select the connection and say 'new' | 19:12 |
| @nirik | http://virt-manager.et.redhat.com/screenshots/install.html | 19:12 |
| @nirik | these screens have changed somewhat in new fedora (f11 at least) to get simplified a bit. | 19:13 |
| @nirik | basically you tell it a name, a arch type, what backend to use, what storage to use, network, mem, cpu. | 19:13 |
| @nirik | and it creates it for you. | 19:13 |
| @nirik | Let me touch a bit on storage. | 19:14 |
| @nirik | You can set libvirt to use various storage backends. lvm, or physical raw partitions or files on your existing filesystem. | 19:14 |
| @nirik | The default is just files on your filesystem, which is very easy to manage, but possibly less performance wise. | 19:14 |
| @nirik | You can use things like iscsi or the like as well. | 19:15 |
| @nirik | anyone have any questions on the gui so far? | 19:15 |
| @nirik | virt-manager is nice, but I think the command line tools are very good. | 19:16 |
| @nirik | There are a set of them: virt-top, virt-df, virt-viewer, and the best of all: virsh | 19:16 |
| @nirik | the various utils like virt-top, virt-df let you run those unix commands on a specific guest from the command line. | 19:17 |
| @nirik | virt-viewer lets you connect to a guest a bring up a vnc console for it. | 19:17 |
| @nirik | virsh has a ton of commands | 19:18 |
| @nirik | http://scrye.com/pastebin/600 is a list I get here on a rawhide server | 19:18 |
| @nirik | vmware has something like this with its vmware-cmd, but thats very limited next to virsh, IMHO | 19:18 |
| @nirik | common things I do with virsh: | 19:19 |
| @nirik | 'virsh list' and 'virsh list --all' shows you all active guests, and all guests defined. | 19:20 |
| @nirik | 'virsh shutdown <name>' and 'virsh start <name>' stops and starts guest | 19:20 |
| @nirik | 'virsh console <name>' gets you a serial console on a guest. | 19:21 |
| subfusc | nirik: and by guest you mean guest user, not guest OS? | 19:21 |
| @nirik | no, I mean guest os... the virtual instance... | 19:22 |
| @herlo | virsh also has a interactive mode I like | 19:22 |
| @nirik | let me give an example from a machine here: | 19:22 |
| @nirik | # virsh list | 19:22 |
| @nirik | Id Name State | 19:22 |
| @nirik | ---------------------------------- | 19:22 |
| @nirik | 1 thulsadoom running | 19:22 |
| @nirik | # ps axuww | grep thulsa | 19:23 |
| @nirik | root 3657 20.5 29.0 2847016 2360028 ? Sl Apr18 4369:18 /usr/bin/qemu-kvm -S -M pc -m 2048 -smp 4 -name thulsadoom -uuid 29bb3791-3007-da35-9919-2466ea425ba1 -monitor pty -pidfile /var/run/libvirt/qemu//thulsadoom.pid -boot c -drive file=/var/lib/libvirt/images/thulsadoom.img,if=ide,index=0,boot=on -net nic,macaddr=00:16:3e:38:e2:98,vlan=0,model=virtio -net tap,fd=16,script=,vlan=0,ifname=vnet0 -serial none -parallel none -usb -vnc 127.0.0.1:0 | 19:23 |
| @nirik | you can see this is a kvm instance. | 19:23 |
| @nirik | all those things on the kvm command line are taken care of for me by libvirt. | 19:23 |
| @nirik | since I defined this guest to have 2048mb memory, 4 cpus, the name and uid it does, the disk image, etc. | 19:24 |
| @nirik | yes, you can also run 'virsh' and get a interactive mode where you can do a set of commands... | 19:24 |
| @nirik | subfusc: does that make sense? | 19:24 |
| @nirik | ok, any further questions on those tools? | 19:25 |
| subfusc | nirik: do i got it right if i think by running virsh stop <name> you kill the kvm instance? | 19:25 |
| pluvo | What is the difference between "virsh -c qemu:///system" and "virsh -c qemu:///session"? | 19:25 |
| @herlo | nirik: yes, I have one about virsh | 19:25 |
| @herlo | specifically, I'd like to create a guest using the interactive mode, then save that out so it can be duplicated, how hard is that? | 19:26 |
| @nirik | subfusc: yes. well, 'shutdown', but right. ;) | 19:26 |
| @nirik | pluvo: good question. I always have used system and thats the default. I am unsure what session is there... | 19:26 |
| @nirik | herlo: several ways. Perhaps the easiest is to make your template guest and copy the xml file and then use a 'virsh define <file.xml>' on it. | 19:27 |
| @nirik | I just realized I left out 'virt-install'. | 19:27 |
| @nirik | It's a command line version of the new guest procedure. It will ask you for memory, name, etc... or you can pass those as arguments to create a guest all from the command line. | 19:28 |
| @nirik | herlo: so, you could just make a virt-install command line with all your parameters filled in as you like too. | 19:28 |
| @nirik | I would like to touch on the guest config format that libvirt uses for a few here. | 19:29 |
| @nirik | libvirt stores info about each guest in a xml file. Those files are located under /etc/libvirt/ | 19:30 |
| @nirik | this xml format describes all the things about that guest libvirt needs to know to start/stop/manage it. | 19:30 |
| @nirik | here's an example of a simple one: http://scrye.com/pastebin/601 | 19:31 |
| @nirik | if you are comfortable with xml or just want to do something that the command line or gui interfaces don't do, you can edit this xml and define guests by loading that xml file | 19:32 |
| @nirik | herlo: oh, there is also 'virt-clone' to clone a template guest to another. | 19:33 |
| @nirik | ok, any questions on the xml or anything else? ;) | 19:33 |
| pluvo | here | 19:34 |
| pluvo | if i edit the xml file under /etc/libvirt/... how can i tell the libvirt-daemon to reload this? | 19:34 |
| pluvo | Normally i edit the xml file with "virsh edit" | 19:34 |
| @nirik | pluvo: the only ways I know are: restart libvirtd. Or 'undefine' the guest and 'define' it again. I don't know of any easier way. | 19:35 |
| @herlo | nirik: oh, nice | 19:35 |
| @herlo | nirik: that's closer to what I was after... | 19:36 |
| @nirik | pluvo: just out of curiosity, what do you need to edit usually? | 19:36 |
| @nirik | ok, I would like to mention a few cool related items to libvirt here before we run low on time: | 19:37 |
| pluvo | i changed the network device to "e1000" | 19:38 |
| @nirik | virt-p2v is a pretty cool livecd for transfering a physical host to a guest on a libvirt server. | 19:38 |
| @nirik | http://et.redhat.com/~rjones/virt-p2v/ | 19:38 |
| @nirik | pluvo: ah, yeah, I hope that is configurable via the tools soon. | 19:38 |
| @nirik | basically with virt-p2v, you download and make this livecd, then boot it and it manages transfering that host to a guest on a libvirt server. It handles the transfer of data and setup on the libvirt side. | 19:39 |
| @nirik | very handy to move a machine to a virtual you want to no longer run as a physical machine. | 19:39 |
| @nirik | And I also wanted to mention libguestfs. This is a library that lets you manipulate guest disk images... you just need access to the image. | 19:40 |
| @nirik | You can use that to do cool things like script changes over a pool of guests. Or modify config without having to boot guests. | 19:41 |
| @nirik | see http://rwmj.wordpress.com/2009/04/29/contributing-a-libguestfs-enhancement-with-examples/ for more info on that | 19:41 |
| @nirik | any other further questions from the floor? | 19:42 |
| @herlo | nirik: what about partitioning a disk img file, can libguestfs do that? I know it used to be done with kpartx, but I never learned that tool... | 19:42 |
| @nirik | herlo: I think it requires the existing image already, and just manipulates the contents... I don't think it can partition. | 19:43 |
| @herlo | the idea being that if the host is in a file, it's difficult to expand / partition, etc. | 19:43 |
| Acedip | why actually do we need libvirt, virtualization backends like xen, vbox doesn use it eveywhere ? | 19:43 |
| @herlo | nirik: ok | 19:43 |
| @nirik | Acedip: well, because it puts a standard frontend on those things. You don't need to care what backend it's using (usually). | 19:44 |
| @nirik | you can manage them the same if they are virtualbox or kvm or xen. | 19:44 |
| @nirik | just need to learn one set of commands and such. ;) | 19:44 |
| @nirik | also, libvirt is fully open (LGPL ed) so it gets rapid improvement and feedback from users. | 19:45 |
| @herlo | nirik: so let's ask an obvious question. And it's probably not something anyone knows for sure. Xen functionality is currently not available in Fedora. Will it be coming back? | 19:46 |
| @nirik | herlo: yeah, I don't know the answer for sure, but it is still being worked on. There are some devel/testing kernels for f11 with Xen Dom0 support. | 19:46 |
| @herlo | oh? I thought for sure it'd be at least F12, that's good to hear... | 19:46 |
| @nirik | and they are working on merging things upstream. So, perhaps f12 or f13 will have support back for xen Dom0 | 19:47 |
| @nirik | yeah, nothing official for f11, but it's being worked on. | 19:47 |
| * nirik checks his notes to see what else he wanted to cover. | 19:47 | |
| @herlo | I did see the stuff for f12, but didn't know there was anything going on for f11 :) | 19:47 |
| @nirik | oh yeah, virt-viewer. So, virt-viewer lets you connect to a vnc console on a guest, so you can run and use gui programs | 19:48 |
| @nirik | A nice new feature in f11 will be that the resolution has been increased and the mouse handling is wonderful now. | 19:48 |
| @nirik | virt-viewer also lets you send various keys to the guest... | 19:49 |
| @nirik | control-alt-del, control-alt-f2, etc... you can also scale it to fit in your client session and take screenshots. | 19:50 |
| * kdn applauds | 19:50 | |
| @nirik | you can connect via a ssh transport from your desktop to the server running libvirt easily by passing it a -c string. | 19:50 |
| @nirik | for example here, I would use 'virt-viewer --connect qemu+ssh://root@theleb/system thulsadoom' | 19:51 |
| @nirik | most of the tools take this --connect argument. In this case thats qemu(really kvm) via ssh and root on the machine 'theleb' connecting to guest 'thulsadoom' | 19:51 |
| @nirik | so it's a secure fast gui console on the guest | 19:51 |
| @nirik | the mouse handling has been vastly improved by changing the guest mouse device to a tablet. ;) | 19:53 |
| @nirik | that way there is absolute control over where the pointer is. | 19:53 |
| @nirik | any questions on virt-viewer? | 19:54 |
| @nirik | oh, one thing I failed to mention when talking about storage: | 19:54 |
| @nirik | You can use a file on your server to contain the guest disk space. You can also tell libvirt to use a 'sparse' file. This means that if you assign a 20GB drive to a guest, and make it a file it will not allocate all 20GB of that, only as data fills it up. | 19:55 |
| @nirik | doing this you can have guests with more space than your host, but of course if they fill up your host drive, it could cause data loss on the guests. | 19:55 |
| * jayson_r has a question about that | 19:56 | |
| @nirik | You can also make new virtual drives and attach them to guests anytime you like. | 19:56 |
| @nirik | jayson_r: ask away. | 19:56 |
| jayson_r | Is there a performance difference between a sparse file and a fully allocated file? I've found that there is under VirtualBox and VMware in the past. | 19:56 |
| @nirik | good question. I tend to do sparse ones... but I don't think I have benchmarked it with a allocated one. | 19:57 |
| @nirik | I don't know, but might be fun to benchmark. ;) | 19:57 |
| @nirik | also, lvm and raw partition would be nice cases to throw in there. | 19:58 |
| pluvo | The default storage pool is '/var/lib/libvirt/images/', right? How can i change this? | 19:58 |
| @nirik | pluvo: yes, you can do a 'virsh pool-edit' and define a new pool, or I think virt-manager has a way to define one. | 19:58 |
| jayson_r | pluvo: in virt-manager | 19:59 |
| @nirik | note that selinux expects guests images to be in that dir, so you may run into selinux issues if you pick another. | 19:59 |
| jayson_r | edit - host details | 19:59 |
| jayson_r | storage tab | 19:59 |
| * nirik nods. | 19:59 | |
| @nirik | Also in f11 we have svirt. | 20:00 |
| jayson_r | svirt? | 20:00 |
| @nirik | basically this is selinux protecting guests from each other and the host. ;) | 20:00 |
| jayson_r | oh | 20:00 |
| @nirik | Features/SVirt_Mandatory_Access_Control | 20:00 |
| @nirik | pretty nice stuff to keep guests and host from compromising each other. | 20:01 |
| @nirik | ok, anyone have any further questions? or shall we wrap things up? | 20:01 |
| @nirik | ok, lets call it a class. ;) | 20:02 |
| @nirik | thanks for coming everyone. | 20:02 |
| DiscordianUK | Thanks nirik | 20:02 |
| kdn | Thanks, nirik. Well done! | 20:02 |
| @nirik | I'd be happy to answer further questions here or in #fedora. | 20:02 |
| * subfusc is glad nirik had this session, and thanks nirik for the wonderfull class, and answering his stupid questions | 20:02 | |
| jayson_r | nirick: awesome job - thanks for your time | 20:02 |
| homerofutoi | thank you nirik, good explaination | 20:03 |
| jayson_r | nirik: sorry for the misspell :-) | 20:03 |
| @nirik | questions are good. ;) | 20:03 |
| @nirik | libvirt is great stuff. | 20:03 |
| pluvo | nirik, thanks! | 20:03 |
| * nirik notes there is still 4 hours left of the teaching day if anyone wants to step up and teach a last minute class. | 20:04 | |
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