[ubuntu] KVM/libvirt VM console access?

z0mbix

I'm setting up KVM and libvirt on hardy. Everything is working ok if I use VNC to install the hosts, but I wish to use the cli to administer these VMs instead of VNC. I have the following VMs running:

root@vm-host-dmz:~# virsh list
Connecting to uri: qemu:///system
Id Name State
----------------------------------
28 DevVM-01 running
30 DevVM-02 running

When I try to access the console, I get the following error:

root@vm-host-dmz:~# virsh console DevVM-01
Connecting to uri: qemu:///system
No console available for domain

root@vm-host-dmz:~#

I want the KVM equivalent of xm console DevVM-01.

How can I setup console access? If I define a console in the xml config file and virsh define it, the console settings just get removed.

geekshlby · 04:51 PM

Check to determine if a console is defined for a VM:

virsh ttyconsole DevVM-01

If null is returned define one:

virsh edit DevVM-01

Example working console:

Code:

<serial type='pty'>
 <source path='/dev/pts/2'/>
 <target port='0'/>
</serial>
<console type='pty' tty='/dev/pts/2'>
 <source path='/dev/pts/2'/>
 <target port='0'/>
</console>

Note: using "virsh edit" will check syntax and redefine the VM for you once you exit the editing environment.

z0mbix

Thanks for the reply. I'm running Hardy. virsh doesn't seem to have the edit command. I have libvirt-bin version 0.4.0-2ubuntu8.1. Any other ideas? Maybe hardy's older version or libvirt-bin doesn't support consoles.

vertigo23

I'm running hardy also, and adding the <serial> and <console> devices isn't working for me. Here's my domain XML:

Code:

<domain type='kvm' id='2'>
  <name>mp-testbed01</name>
  <uuid>b996eded-ed4c-d6b6-d28d-13443849070e</uuid>
  <memory>262144</memory>
  <currentMemory>262144</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type>hvm</type>
    <boot dev='hd'/>
  </os>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/home/AUTOHOME/alex/VMs/p4-hot/root.qcow2'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <interface type='network'>
      <mac address='52:54:00:e7:35:c2'/>
      <source network='default'/>
      <target dev='vnet1'/>
    </interface>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5900' listen='10.10.4.57'/>
    <serial type='pty'>
     <source path='/dev/pts/2'/>
     <target port='0'/>
    </serial>
    <console type='pty' tty='/dev/pts/2'>
     <source path='/dev/pts/2'/>
     <target port='0'/>
    </console>
  </devices>
</domain>

When I run "virsh define domain.xml", it doesn't error, but neither the serial nor the console sections show up when I then dump the XML in virsh.

Blinkiz

am also looking for the answer to this.
So am bumping this one and subscribing to this thread.

netangel

There is a solution.

Just after starting the VM, you can do :

Code:

sudo tail /var/log/libvirt/qemu/<vm_name>.log

Here is a sample reply :

Code:

/usr/bin/kvm -M pc -m 2048 -smp 4 -monitor pty -drive file=/var/lib/libvirt/images/<vm_name>.img,if=ide,boot=on -net nic,macaddr=00:16:ff:09:28:1e,vlan=0 -net tap,fd=4,script=,vlan=0 -usb -vnc 127.0.0.1:1 
char device redirected to /dev/pts/1

The last line is really important. It tells you that kvm console is accessible to /dev/pts/X tty. Here, X is 1.

Install the socat command (sudo apt-get install socat) and type in :

Code:

sudo socat - /dev/pts/1

You are now connected to kvm console. Type for example :

Code:

info snapshots

or any other kvm command.

BE CAREFUL, to exit from that console, just press Ctrl+C (to quit socat actually).

My problem now is when the VM has run for a while, there is no more the "char device redirected to /dev/pts/X" in the logs ... so I search a method to retreive the actual pts which the VM points to.

If you look at the file descriptors of the kvm VM (lsof -p <kvm_process_number>, you found :

Code:

...
kvm     6249 root   10u   CHR    5,2                 1675 /dev/ptmx
...

The process has opened /dev/ptmx. The problem I'm facing is that I don't know any mean of retreiving the pts part (the slave part) of that opened master tty. There is just a C function called "ptsname", but I didn't find a script command to do the same ... Does someone know about that ?

nullzone

Another way is to define a serial console.

Add a serial device to be used as a conseole in the libvirt XML file of your virtual machine (it is a device so, add that inside the <device></devices> directives):

Code:

<serial type="pty">
      <source path="/dev/pts/3"/>
      <target port="1"/>
    </serial>

Go into your Virtual machine (use ssh, vnc or anyway) and define a tty to be used as a serial console. To do this just create a new upstart script, lets say /etc/init/ttyS0.conf with this code:

Code:

# ttyS0 - getty
#
# This service maintains a getty on ttyS0 from the point the system is
# started until it is shut down again.

start on stopped rc RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn
exec /sbin -L 38400 ttyS0 vt102

In your core server, reload your libvirt-bin and reboot the machine (it is necesary so the kernel will detect the new serial defined previously in your VM XML file):

Code:

$ sudo reload libvirt-bin
$ sudo virsh shutdown <your_vm_name>
... wait ...
$ sudo virsh start <your_vm_name>

You will see the serial in your kernel/dmesg logs after the boot as follow:

serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
00:05: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

It is all ... you have now a console defined and up-&-running. To log on in your virtual machine you can now use:

Code:

$ sudo virsh console <your_vm_name>

----

Aditionally, you could get the boot-messages in the console and not only a login console after the full boot just editiing inside the virtual machine the /etc/default/grub file as follow:

Code:

GRUB_CMDLINE_LINUX="console=ttyS0,38400n8 console=tty0"

Some ppl talk about setting the GRUB_TERMINAL variable with a "serial" value so your should have a complete serial access from the beginning to the grub boot. Tbh, I havent need this yet so... if anybody have done any test I'd apreciate a clear input about how to get this working correctly.

Cheers,

Nullzone

Blinkiz

Nice guide nullzone, thanks

Harpette

Quote:

Originally Posted by nullzone

In my (limited) experience, specifying a source path is unnecessary, since it automatically gets assigned one after you boot the vm. Also, a target port of "0" works for me.

Quote:

create a new upstart script, lets say /etc/init/ttyS0.conf

I read elsewhere a same script defined as /etc/event.d/ttyS0 ; what's the difference ? Which is better / more appropriate ?

Quote:

In your core server, reload your libvirt-bin:

$ sudo reload libvirt-bin

Don't need to do that, perhaps because i didn't specify a source path above

Other than these, thanks Nullzone for your guide which did help me much.

addihetja

I followed these directions but I still can't connect to the console:

Quote:

virsh # start Ubuntu804
Domain Ubuntu804 started

virsh # console Ubuntu804
No console available for domain

This is what I got from /var/log/libvirt/qemu/Ubuntu804.log:

Quote:

LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin QEMU_AUDIO_DRV=none /usr/bin/kvm -S -M pc-0.12 -enable-kvm -m 2048 -smp 1 -name Ubuntu804 -uuid 3e5f089d-dc8b-a642-c108-d3408d040230 -chardev socket,id=monitor,path=/var/lib/libvirt/qemu/Ubuntu804.monitor,server,nowait -monitor chardev:monitor -boot c -drive file=/home/truenorth/ubuntu-kvm/tmpfAmN6M.qcow2,if=ide,index=0,boot=on,format=qcow 2 -net nic,macaddr=52:54:00:ad:da:bf,vlan=0,model=virtio, name=virtio.0 -net tap,fd=55,vlan=0,name=tap.0 -chardev null,id=serial0 -serial chardev:serial0 -parallel none -usb -vnc 127.0.0.1:0 -vga cirrus
pci_add_option_rom: failed to find romfile "pxe-virtio.bin"

Here is my /etc/libvirt/qemu/Ubuntu804.xml file:

Quote:

<domain type='kvm'>
<name>Ubuntu804</name>
<uuid>3e5f089d-dc8b-a642-c108-d3408d040230</uuid>
<memory>2097152</memory>
<currentMemory>2097152</currentMemory>
<vcpu>1</vcpu>
<os>
<type arch='x86_64' machine='pc-0.12'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>
<devices>
<serial type='tty'>
<source path='/dev/ttyS0'/>
<target port='0'/>
</serial>
<console type='tty' tty='/dev/ttyS0'>
<source path='/dev/ttyS0'/>
<target port='0'/>
</console>
<emulator>/usr/bin/kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/home/admin/ubuntu-kvm/tmpfAmN6M.qcow2'/>
<target dev='hda' bus='ide'/>
</disk>
<interface type='bridge'>
<mac address='52:54:00:ad:da:bf'/>
<source bridge='br0'/>
<model type='virtio'/>
</interface>
<input type='mouse' bus='ps2'/>
<graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'/>
<video>
<model type='cirrus' vram='9216' heads='1'/>
</video>
</devices>
</domain>

Here is my /etc/init/ttyS0.conf:

Quote:

s service maintains a getty on ttyS0 from the point the system is
# started until it is shut down again.

start on stopped rc RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn
exec /sbin -L 38400 ttyS0 vt102

There is no GUI installed on the server (which is running 11.04, btw) so I need to run virsh. I've tried all sorts of variations of this ( f.x.