KVM: Tips and Tricks - Revision history

David at 11:06, 27 January 2016

2016-01-27T11:06:21Z

David: /* Create an internal network on a KVM host */

2015-06-08T19:15:55Z

Create an internal network on a KVM host

David: /* Create an internal network on a KVM host */

2015-05-14T11:27:23Z

Create an internal network on a KVM host

David at 11:19, 14 May 2015

2015-05-14T11:19:34Z

David at 13:40, 7 November 2012

2012-11-07T13:40:50Z

David: Created page with "= KVM Tips and Tricks = == VNC / Args == CLI Args: -alt-grab - makes ctrl+alt+shift the key escape rather than ctrl+alt (which makes it impossible for windows logins) ..."

2012-11-07T13:40:38Z

Created page with "= KVM Tips and Tricks = == VNC / Args == <syntaxhighlight> CLI Args: -alt-grab - makes ctrl+alt+shift the key escape rather than ctrl+alt (which makes it impossible for windows logins) ..."

New page

= KVM Tips and Tricks =

== VNC / Args ==
<syntaxhighlight>
CLI Args:
-alt-grab - makes ctrl+alt+shift the key escape rather than ctrl+alt (which makes it impossible for windows logins)
on vncviewer, you can also hit f8 to bring up a menu which will allow
-smp n (number of cores to allocate)
-m 8192 (amount of memory to give the machine)
-net nic -net nic (give the system two nics)
</syntaxhighlight>

== Mounting NFS in VM ==
ERROR: mountd: refused mount nfs illegal port

In case you’re getting error while mounting a nfs share, and logs on server showing:
<syntaxhighlight>
Mar 24 10:44:57 localhost mountd[8344]: refused mount request from 192.168.1.2 for /dump (/dump): illegal port 52213
</syntaxhighlight>

Add insecure option in your exports file:
<syntaxhighlight>
/dump *(ro,sync,no_root_squash,insecure)

# And do
exportfs -r # or reload/restart nfs service.
</syntaxhighlight>

== Grow a KVM Disk Image (RAW) ==
E.G to grow a KVM image by 10G (Perhaps this could be a hell of a lot easier with LVM)
* Create additional space as a raw qemu-img
* cat the two files together
* Boot gparted-live to resize partitions/filesystem
<syntaxhighlight>
[root@kvm vm]$ qemu-img create -f raw guest1-rhel6-64-largerdisk 10G
Formatting 'guest1-rhel6-64-largerdisk', fmt=raw size=10737418240
[root@kvm vm]$ ll
total 17611676
-rwxrwxrwx. 1 root root 10737418240 Sep 27 14:34 guest1-rhel6-64
-rwxr-xr-x 1 root root 10737418240 Sep 27 13:14 guest1-rhel6-64-clone
'-rw-r--r-- 1 root root 10737418240 Sep 27 14:37 guest1-rhel6-64-largerdisk'
[root@kvm vm]$ cat guest1-rhel6-64 guest1-rhel6-64-largerdisk > sl6-30g-puppetcobbler.kvm
[root@kvm vm]$ ll
total 38583200
-rwxrwxrwx. 1 root root 10737418240 Sep 27 14:34 guest1-rhel6-64
-rwxr-xr-x 1 root root 10737418240 Sep 27 13:14 guest1-rhel6-64-clone
-rw-r--r-- 1 root root 10737418240 Sep 27 14:37 guest1-rhel6-64-largerdisk
'-rw-r--r-- 1 root root 21474836480 Sep 27 14:42 sl6-30g-puppetcobbler.kvm'
</syntaxhighlight>

Just as easy to convert a raw image to qcow2 and then resize that(<tt>qemu-img resize [vmname.qcow2] +100G</tt>). Use LVM as below to grow the FS.

Now boot up a ubuntu (or other) live cd (in virt-manager: add hardware -> storage -> select managed.. -> device type -> IDE CDrom)
Install lvm tools: apt-get install lvm2
Fdisk create new partition:
fdisk /dev/sda
delete lvm partition (d -> 2 in this instance)
create lvm partition (same cylinder start, new end pick the default which will be the last cylinder) (n -> p -> start / finish)
change type of new partition to lvm (t -> 8e)

Use LVM to grow the volume
<syntaxhighlight>
root@ubuntu:~# pvdisplay /dev/sda2
--- Physical volume ---
PV Name /dev/sda2
VG Name vg_puppetmaster
PV Size 9.51 GiB / not usable 3.00 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 2434
Free PE 0
Allocated PE 2434
PV UUID LBxPCN-RL3d-rd7d-qEcr-M5Fq-GfMF-ttiPPd

root@ubuntu:~# partprobe
Warning: Unable to open /dev/sr0 read-write (Read-only file system). /dev/sr0 has been opened read-only.
root@ubuntu:~# pvresize /dev/sda2
Physical volume "/dev/sda2" changed
1 physical volume(s) resized / 0 physical volume(s) not resized
root@ubuntu:~# pvdisplay /dev/sda2
--- Physical volume ---
PV Name /dev/sda2
VG Name vg_puppetmaster
PV Size 19.50 GiB / not usable 3.46 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 4992
Free PE 2558
Allocated PE 2434
PV UUID LBxPCN-RL3d-rd7d-qEcr-M5Fq-GfMF-ttiPPd

t@ubuntu:~# vgchange -a y vg_puppetmaster
2 logical volume(s) in volume group "vg_puppetmaster" now active
root@ubuntu:~# vgdisplay vg_puppetmaster
--- Volume group ---
VG Name vg_puppetmaster
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 4
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 0
Max PV 0
Cur PV 1
Act PV 1
VG Size 19.50 GiB
PE Size 4.00 MiB
Total PE 4992
Alloc PE / Size 2434 / 9.51 GiB
Free PE / Size 2558 / 9.99 GiB
VG UUID Bu7xaM-OQrj-aZYV-gwY8-MvXg-Az1m-8wZh6p

root@ubuntu:~# lvextend -L +10G /dev/vg_puppetmaster/lv_root
Extending logical volume lv_root to 15.57 GiB
Insufficient free space: 2560 extents needed, but only 2558 available

root@ubuntu:~# lvextend -L +9.9G /dev/vg_puppetmaster/lv_root
Rounding up size to full physical extent 9.90 GiB
Extending logical volume lv_root to 15.47 GiB
Logical volume lv_root successfully resized

root@ubuntu:~# resize2fs /dev/vg_puppetmaster/lv_root
resize2fs 1.41.14 (22-Dec-2010)
Please run 'e2fsck -f /dev/vg_puppetmaster/lv_root' first.

root@ubuntu:~# e2fsck -f /dev/vg_puppetmaster/lv_root
e2fsck 1.41.14 (22-Dec-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/vg_puppetmaster/lv_root: 50681/365760 files (0.1% non-contiguous), 448889/1460224 blocks
root@ubuntu:~# resize2fs /dev/vg_puppetmaster/lv_root
resize2fs 1.41.14 (22-Dec-2010)
Resizing the filesystem on /dev/vg_puppetmaster/lv_root to 4056064 (4k) blocks.
The filesystem on /dev/vg_puppetmaster/lv_root is now 4056064 blocks long.

root@ubuntu:~# lvscan
ACTIVE '/dev/vg_puppetmaster/lv_root' [15.47 GiB] inherit
ACTIVE '/dev/vg_puppetmaster/lv_swap' [3.94 GiB] inherit

</syntaxhighlight>

== Use old VM img with virt-manager ==
You'll need to use virt-manager to import an old file. Point this towards an existing raw VM and import. Import didnt add a CD drive, so used the command:

<syntaxhighlight>
[root@kvm vm]$ /usr/libexec/qemu-kvm -hda ./sl6-30g-puppetcobbler.kvm \
-cdrom /mnt/vstor/gparted-live/gparted-live-0.7.1-1.iso -m 512 -boot d
Using CPU model "cpu64-rhel6"
VNC server running on `::1:5900'

# Then vmcviewer on another terminal
vncviewer localhost:5900
</syntaxhighlight>

== Copying VMs udev renames network ==
* udev seems to be adding lines in /etc/udev/70-persistent-net.rules
* Remove entries and set MAC correctly
* Also had to update the files in /etc/sysconfig/network-scripts/ifcfg-eth0 to remove/change the MAC address
* All this could probably have been avoided if i set the MAC correctly when setting up the machine? (not tested)

== Disable DHCP on KVM Server ==
In this example i wanted to run a virtual DHCP server on the KVM system. The KVM server was getting in the way as it run a DHCP service also. To disable, remove the <tt><dhcp></tt> tags from the file <tt>/var/lib/libvirt/network/default.xml</tt>

Change from:
<syntaxhighlight>
<network>
<name>default</name>
<uuid>319d4ae5-4b6e-433c-832f-ad20269ed495</uuid>
<forward mode='nat'/>
<bridge name='virbr0' stp='on' delay='0' />
<mac address='52:54:00:09:89:76'/>
<ip address='192.168.122.1' netmask='255.255.255.0'>
<dhcp>
<range start='192.168.122.2' end='192.168.122.254' />
</dhcp>
</ip>
</network>
</syntaxhighlight>

Change to:
<syntaxhighlight>
<network>
<name>default</name>
<uuid>319d4ae5-4b6e-433c-832f-ad20269ed495</uuid>
<forward mode='nat'/>
<bridge name='virbr0' stp='on' delay='0' />
<mac address='52:54:00:09:89:76'/>
<ip address='192.168.122.1' netmask='255.255.255.0'>
</ip>
</network>
</syntaxhighlight>

And then restart libvirtd and dnsmasq:
<syntaxhighlight>
service libvirtd restart
service dnsmasq restart
</syntaxhighlight>

== Important Config Files ==
Important Configuration And Log Files (Directories) Location

The following files are required to manage and debug KVM problems:

1. /etc/libvirt/ - Main configuration directory.
2. /etc/libvirt/qemu/ - Virtual machine configuration directory. All xml files regarding VMs are stored here. You can edit them manually or via virt-manager.
3. /etc/libvirt/qemu/networks/ - Networking for your KVM including default NAT. NAT is only recommended for small setup or desktops. I strongly suggest you use bridged based networking for performance.
4. /etc/libvirt/qemu/networks/default.xml - The default NAT configuration used by NAT device virbr0.
5. /var/log/libvirt/ - The default log file directory. All VM specific logs files are stored here.
6. /etc/libvirt/libvirtd.conf - Master libvirtd configuration file.
7. /etc/libvirt/qemu.conf - Master configuration file for the QEMU driver.

== Editing the VM XML ==
libvirt stores it's configuration as xml in '/etc/libvirt/qemu'. The xml is easy to understand, and is similar to VMware *.vmx files. While it is possible to edit these files in place and restart libvirt-bin for the changes to take affect, the recommended method for modifying the attributes of a virtual machine is via virsh (or virt-manager, if it supports changing the hardware you want to change). The concept is simple:

1. export (aka 'dump') the xml of the virtual machine you want to edit
2. edit the xml
3. import (aka 'define') the xml

For example, to edit the machine named 'foo' (you can get a list of your machines with 'virsh list --all'), do:

<syntaxhighlight>
$ virsh dumpxml foo > /tmp/foo.xml
(edit /tmp/foo.xml as needed)
$ virsh define /tmp/foo.xml
</syntaxhighlight>

@@ Line 307: / Line 307: @@
 # Then you can add hardware in the VM; Add NIC; Select internal network;
 # Any nodes on the hosts can communicate on this network, no access to outside world.
 </syntaxhighlight>

@@ Line 238: / Line 238: @@
 <syntaxhighlight>
 [root@ivy4 ~]# cat internalnetwork.xml
 <network connections='1'>

@@ Line 235: / Line 235: @@
 == Create an internal network on a KVM host ==
 <syntaxhighlight>
 [root@ivy4 ~]# cat internalnetwork.xml

← Older revision		Revision as of 13:40, 7 November 2012
Line 1:		Line 1:
−	~~= KVM Tips and Tricks =~~	+

	== VNC / Args ==		== VNC / Args ==

@@ Line 232: / Line 232: @@
    (edit /tmp/foo.xml as needed)
    $ virsh define /tmp/foo.xml
 </syntaxhighlight>