Difference between revisions of "Talk:QEMU"

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When I was updating the article yesterday, I had tried to fit the section about linear raid (boot a VM from a partition by prepending a MBR to it) into the article better.  But I'm not sure the technique described is the right one at all.  It looks like it works, but wouldn't it be easier to install a bootloader directly to the partition (e.g. syslinux)?  Then the VM could be booted directly from the partition simply by using it as its virtual disk.
 
When I was updating the article yesterday, I had tried to fit the section about linear raid (boot a VM from a partition by prepending a MBR to it) into the article better.  But I'm not sure the technique described is the right one at all.  It looks like it works, but wouldn't it be easier to install a bootloader directly to the partition (e.g. syslinux)?  Then the VM could be booted directly from the partition simply by using it as its virtual disk.
 
--[[User:Synchronicity|Synchronicity]] ([[User talk:Synchronicity|talk]]) 19:23, 9 May 2012 (UTC)
 
--[[User:Synchronicity|Synchronicity]] ([[User talk:Synchronicity|talk]]) 19:23, 9 May 2012 (UTC)
 
== qemu-* vs qemu-system-*? ==
 
 
What's the difference between qemu-* and qemu-system-*? So far, I haven't seen too much of a difference, except for a quite noticeable difference in filesize:
 
 
{{bc|
 
# ls -l $(which qemu{-system,}-x86_64);
 
-rwxr-xr-x 1 root root 4793008 Jun  8 02:14 /usr/bin/qemu-system-x86_64
 
-rwxr-xr-x 1 root root 2406208 Jun  8 02:14 /usr/bin/qemu-x86_64
 
}}
 
 
: Next time please add a signature after your post by typing four tildes ({{ic|<nowiki>~~~~</nowiki>}}). Thanks.
 
: There have been some changes recently and the wiki page isn't yet fully updated. I guess that the old {{ic|qemu}} binary has been replaced by {{ic|qemu-system-*}} depending on architecture and {{ic|qemu-*}} binary is used internally. See qemu(1) for more details.
 
: -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 09:47, 16 July 2013 (UTC)
 
 
::I've done some more research on this: {{ic|qemu-system-*}} binaries emulate full virtual machine (that's currently described in [[QEMU]], some time ago {{ic|qemu}} was used for this purpose), whereas {{ic|qemu-*}} binaries allow executing statically linked binaries for different architecture than the host system. You can even [http://www.gentoo.org/proj/en/base/embedded/handbook/?part=1&chap=5 chroot] into different-architecture system emulating even dynamically linked binaries. Perhaps some mention of this could be added to [[QEMU]]. -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 20:54, 22 July 2013 (UTC)
 
  
 
== Creating bridge manually ==
 
== Creating bridge manually ==
  
 
I really don't know what to do with this section. I'd say it has been superseded by [[QEMU#Creating bridge using qemu-bridge-helper]] (available since qemu-1.1, we now have qemu-1.5) - or is someone still using this method? Perhaps link to https://en.wikibooks.org/wiki/QEMU/Networking#TAP_interfaces or http://wiki.qemu.org/Documentation/Networking/NAT is sufficient. What do you think? -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 20:42, 22 July 2013 (UTC)
 
I really don't know what to do with this section. I'd say it has been superseded by [[QEMU#Creating bridge using qemu-bridge-helper]] (available since qemu-1.1, we now have qemu-1.5) - or is someone still using this method? Perhaps link to https://en.wikibooks.org/wiki/QEMU/Networking#TAP_interfaces or http://wiki.qemu.org/Documentation/Networking/NAT is sufficient. What do you think? -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 20:42, 22 July 2013 (UTC)
 +
 +
:Actually, I've become a happy user of this method. I've written some scripts to easily create bridge interface, TAP interface, and combined with Xyne's [http://xyne.archlinux.ca/notes/network/dhcp_with_dns.html excellent scripts] to set up NAT and launch DHCP server, I have complete solution to easily manage multiple VMs on one (or even more) bridge.
 +
:My scripts are available on github: [https://github.com/lahwaacz/archlinux-dotfiles/blob/master/Scripts/qemu-launcher.sh], [https://github.com/lahwaacz/archlinux-dotfiles/blob/master/Scripts/qemu-tap-helper.sh], [https://github.com/lahwaacz/archlinux-dotfiles/blob/master/Scripts/qemu-mac-hasher.py] but I won't probably integrate them into the wiki, I'l just leave a note when I do some more testing.
 +
:The thing is, what to do with the current content? Personally I think that links to [https://en.wikibooks.org/wiki/QEMU/Networking#TAP_interfaces], [http://wiki.qemu.org/Documentation/Networking/NAT] and my scripts are sufficient (of course others are welcome). I'd also leave the note at the end to ''disable the firewall on the bridge'', I find it extremely useful.
 +
:-- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 18:24, 5 September 2013 (UTC)
  
 
==  Preparing an (Arch) Linux guest  ==
 
==  Preparing an (Arch) Linux guest  ==
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:In newer kernel versions (I think since 3.4) the kernel modules are loaded automatically. I'd still keep the section as it is for now, linux-lts is still at 3.0. -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 21:09, 20 August 2013 (UTC)
 
:In newer kernel versions (I think since 3.4) the kernel modules are loaded automatically. I'd still keep the section as it is for now, linux-lts is still at 3.0. -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 21:09, 20 August 2013 (UTC)
  
== Starting QEMU virtual machines with Systemd  ==
+
::{{Pkg|linux-lts}} is now on the 3.10 series.
 +
::-- [[User:Jstjohn|Jstjohn]] ([[User talk:Jstjohn|talk]]) 16:51, 23 September 2013 (UTC)
 +
 
 +
== Starting QEMU virtual machines with systemd ==
 
The custom systemd service script does not work. It always fails with {{ic|Failed at step EXEC spawning /usr/bin/qemu-{type}: No such file or directory}}. To Fix this modify the ExecStart command {{bc|1=ExecStart=/usr/bin/sh -c "/usr/bin/qemu-${type} -name %i -nographic ${args}"}}
 
The custom systemd service script does not work. It always fails with {{ic|Failed at step EXEC spawning /usr/bin/qemu-{type}: No such file or directory}}. To Fix this modify the ExecStart command {{bc|1=ExecStart=/usr/bin/sh -c "/usr/bin/qemu-${type} -name %i -nographic ${args}"}}
Also {{ic|echo 'system_powerdown' &#124; nc localhost 7101}} kills the VM immediatly. To fix this change the stop script. It simply checks each second if the main process is still running. {{bc|1=ExecStop=/usr/bin/sh -c "${haltcmd} && while [[ `pidof qemu-${type} | grep $MAINPID` ]]; do sleep 1; done"}}
+
Also {{ic|echo 'system_powerdown' &#124; nc localhost 7101}} kills the VM immediatly. To fix this change the stop script. It simply checks each second if the main process is still running. {{bc|1=ExecStop=/usr/bin/sh -c "${haltcmd} && while [[ $(pidof qemu-${type} | grep $MAINPID) ]]; do sleep 1; done"}}
 
{{ic|gnu-netcat}} does not work to connect to the monitor. You need to use {{ic|openbsd-netcat}}. -- [[User:Ant32|Ant32]] ([[User talk:Ant32|talk]]) 17:48, 5 September 2013 (UTC)
 
{{ic|gnu-netcat}} does not work to connect to the monitor. You need to use {{ic|openbsd-netcat}}. -- [[User:Ant32|Ant32]] ([[User talk:Ant32|talk]]) 17:48, 5 September 2013 (UTC)
 +
 +
:The first problem related to starting the service seems rather strange - didn't you have typo error in your local {{ic|qemu@.service}} file (missing the dollar sign {{ic|$}} in {{ic|${type} }})?
 +
:The second problem is valid, systemd kills the main process when the ExecStop command exits (see {{ic|systemd.service(5)}}). If your workaround really works, it could be added to the wiki with a proper description.
 +
:-- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 21:17, 7 September 2013 (UTC)
 +
 +
::Relevant thread on systemd-devel mailing list: [http://lists.freedesktop.org/archives/systemd-devel/2013-September/012982.html] -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 00:00, 15 September 2013 (UTC)
 +
 +
== Kexec Hackery When Using a Real Partition ==
 +
 +
After banging my head against a wall long enough and figuring out what {{ic|-kernel}} and {{ic|-initrd}} were really calling, I put a note above the appropriate section and mentioned two ways to use the guest's images.  (Otherwise, you'll have to worry if the host and guest images match.)  The first -- mount the partition(s) -- is more appropriate for "low-volume-handling" of VMs.  The second -- using kexec -- becomes more useful when you're juggling more than a few VMs.
 +
 +
I'm only mentioning this hack because (as of now) [[Kexec]] only mentions use for rebooting into another kernel, not switching out the kernel before the system is even up.  This hack comes from from https://digitalocean.uservoice.com/forums/136585-digitalocean/suggestions/2814988-give-option-to-use-the-droplet-s-own-bootloader- which has two suggestions.  The most recent, using systemd units by jkuan, doesn't work because jkuan tried to copy a {{ic|.target}} file into a {{ic|.service}} file and systemd wants {{ic|ExecStart}} in a {{ic|.service}} file.  The second one, replacing {{ic|/usr/bin/init}} by andrew_sparks, works for me on my Arch instance at DigitalOcean.
 +
 +
Adaptation from said post:
 +
 +
# pacman -S kexec-tools
 +
# pacman -R systemd-sysvcompat
 +
 +
{{hc|1=/tmp/init|2=
 +
#!/bin/sh
 +
 +
kexec --load /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --append="root=/dev/sda init=/usr/lib/systemd/systemd" &&
 +
mount -o ro,remount / && kexec -e
 +
exec /usr/lib/systemd/systemd
 +
}}
 +
 +
# cd [/path/to/vm]/usr/bin
 +
# mv init init.dist
 +
# cp /tmp/init ./
 +
# chmod 755 init
 +
 +
I'm leaving this on the Talk page as I haven't even tried it out in QEMU myself.  Also, my eyes are about ready to pop out of my head, so I'm barring myself from figuring out the appropriate way to edit this in for the time being. [[User:BrainwreckedTech|BrainwreckedTech]] ([[User talk:BrainwreckedTech|talk]]) 21:23, 14 January 2014 (UTC)

Revision as of 10:21, 23 March 2014

Linear RAID

When I was updating the article yesterday, I had tried to fit the section about linear raid (boot a VM from a partition by prepending a MBR to it) into the article better. But I'm not sure the technique described is the right one at all. It looks like it works, but wouldn't it be easier to install a bootloader directly to the partition (e.g. syslinux)? Then the VM could be booted directly from the partition simply by using it as its virtual disk. --Synchronicity (talk) 19:23, 9 May 2012 (UTC)

Creating bridge manually

I really don't know what to do with this section. I'd say it has been superseded by QEMU#Creating bridge using qemu-bridge-helper (available since qemu-1.1, we now have qemu-1.5) - or is someone still using this method? Perhaps link to https://en.wikibooks.org/wiki/QEMU/Networking#TAP_interfaces or http://wiki.qemu.org/Documentation/Networking/NAT is sufficient. What do you think? -- Lahwaacz (talk) 20:42, 22 July 2013 (UTC)

Actually, I've become a happy user of this method. I've written some scripts to easily create bridge interface, TAP interface, and combined with Xyne's excellent scripts to set up NAT and launch DHCP server, I have complete solution to easily manage multiple VMs on one (or even more) bridge.
My scripts are available on github: [1], [2], [3] but I won't probably integrate them into the wiki, I'l just leave a note when I do some more testing.
The thing is, what to do with the current content? Personally I think that links to [4], [5] and my scripts are sufficient (of course others are welcome). I'd also leave the note at the end to disable the firewall on the bridge, I find it extremely useful.
-- Lahwaacz (talk) 18:24, 5 September 2013 (UTC)

Preparing an (Arch) Linux guest

adding the virtio modules to use virtual devices doesn't appear to be necessary as of the VM I built this week(Jul 26, 2013). Kernel 3.9.9-1 Surlyjake (talk) 03:42, 27 July 2013 (UTC)

In newer kernel versions (I think since 3.4) the kernel modules are loaded automatically. I'd still keep the section as it is for now, linux-lts is still at 3.0. -- Lahwaacz (talk) 21:09, 20 August 2013 (UTC)
linux-lts is now on the 3.10 series.
-- Jstjohn (talk) 16:51, 23 September 2013 (UTC)

Starting QEMU virtual machines with systemd

The custom systemd service script does not work. It always fails with Failed at step EXEC spawning /usr/bin/qemu-{type}: No such file or directory. To Fix this modify the ExecStart command
ExecStart=/usr/bin/sh -c "/usr/bin/qemu-${type} -name %i -nographic ${args}"
Also echo 'system_powerdown' | nc localhost 7101 kills the VM immediatly. To fix this change the stop script. It simply checks each second if the main process is still running.
ExecStop=/usr/bin/sh -c "${haltcmd} && while [[ $(pidof qemu-${type} | grep $MAINPID) ]]; do sleep 1; done"

gnu-netcat does not work to connect to the monitor. You need to use openbsd-netcat. -- Ant32 (talk) 17:48, 5 September 2013 (UTC)

The first problem related to starting the service seems rather strange - didn't you have typo error in your local qemu@.service file (missing the dollar sign $ in ${type} )?
The second problem is valid, systemd kills the main process when the ExecStop command exits (see systemd.service(5)). If your workaround really works, it could be added to the wiki with a proper description.
-- Lahwaacz (talk) 21:17, 7 September 2013 (UTC)
Relevant thread on systemd-devel mailing list: [6] -- Lahwaacz (talk) 00:00, 15 September 2013 (UTC)

Kexec Hackery When Using a Real Partition

After banging my head against a wall long enough and figuring out what -kernel and -initrd were really calling, I put a note above the appropriate section and mentioned two ways to use the guest's images. (Otherwise, you'll have to worry if the host and guest images match.) The first -- mount the partition(s) -- is more appropriate for "low-volume-handling" of VMs. The second -- using kexec -- becomes more useful when you're juggling more than a few VMs.

I'm only mentioning this hack because (as of now) Kexec only mentions use for rebooting into another kernel, not switching out the kernel before the system is even up. This hack comes from from https://digitalocean.uservoice.com/forums/136585-digitalocean/suggestions/2814988-give-option-to-use-the-droplet-s-own-bootloader- which has two suggestions. The most recent, using systemd units by jkuan, doesn't work because jkuan tried to copy a .target file into a .service file and systemd wants ExecStart in a .service file. The second one, replacing /usr/bin/init by andrew_sparks, works for me on my Arch instance at DigitalOcean.

Adaptation from said post:

# pacman -S kexec-tools
# pacman -R systemd-sysvcompat
/tmp/init
#!/bin/sh

kexec --load /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --append="root=/dev/sda init=/usr/lib/systemd/systemd" &&
mount -o ro,remount / && kexec -e
exec /usr/lib/systemd/systemd
# cd [/path/to/vm]/usr/bin
# mv init init.dist
# cp /tmp/init ./
# chmod 755 init

I'm leaving this on the Talk page as I haven't even tried it out in QEMU myself. Also, my eyes are about ready to pop out of my head, so I'm barring myself from figuring out the appropriate way to edit this in for the time being. BrainwreckedTech (talk) 21:23, 14 January 2014 (UTC)