Building virtual machines with vmbuilder

After installing qemu-kvm, libvirt-bin, bridge-utils and ubuntu-vm-builder, set up a bridge that virtual machines can attach to:

auto lo
iface lo inet loopback

auto enp2s0
iface enp2s0 inet manual

auto br0
iface br0 inet static
      bridge_ports enp2s0
      bridge_stp off
      bridge_fd 0
      bridge_maxwait 0

Then /etc/init.d/networking restart.

Install apt-cacher and give it the following config in /etc/apt-cacher/apt-cacher.conf:

group = www-data
user = www-data
daemon_addr =
path_map = ubuntu
allowed_hosts =,,,
ubuntu_release_names = trusty

The vm build script, using the local cache:


if [ $# -lt 2 ]; then
    echo "usage: HOSTNAME IP"
    exit 1

echo "#!/bin/bash" >>$firstboot
echo "rm -f /etc/resolvconf/resolv.conf.d/{original,base,head,tail}" >>$firstboot
echo "reboot" >>$firstboot
chmod +x $firstboot

qemu-img create -f qcow2 -o preallocation=falloc $HOME/vms/$HOSTNAME-rootdisk 4096M

vmbuilder kvm ubuntu \
  --suite trusty \
  --verbose \
  --libvirt qemu:///system \
  --destdir $HOME/vms/$HOSTNAME/ \
  --install-mirror \
  --mirror \
  --raw $HOME/vms/$HOSTNAME-rootdisk \
  --rootsize 4096 \
  --swapsize 0 \
  --mem 128 \
  --cpus 1 \
  --hostname $HOSTNAME \
  --bridge br0 \
  --ip $IP\
  --mask \
  --gw \
  --dns \
  --lang en_US.UTF-8 \
  --timezone UTC \
  --user ubuntu \
  --name Ubuntu \
  --pass ubuntu \
  --ssh-user-key $HOME/.ssh/ \
  --addpkg linux-image-generic \
  --addpkg openssh-server \
  --addpkg sudo \
  --firstboot $firstboot

rm $firstboot
rmdir $HOME/vms/$HOSTNAME/

virsh autostart $HOSTNAME
virsh start $HOSTNAME

Edit: To inspect and edit the virtual machine disk image, use guestfish, part of the libguestfs project:

$ sudo apt-get install libguestfs-tools
$ guestfish --rw --add testserver-rootdisk

Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.

Type: 'help' for help on commands
      'man' to read the manual
      'quit' to quit the shell

><fs> run
100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
><fs> list-filesystems
/dev/sda1: ext4
><fs> mount /dev/sda1 /
><fs> emacs /etc/resolv.conf
><fs> exit

Edit: Disk image pre-allocation can be done with QEMU-provided tools, which may or may not be a more kosher approach. Must investigate.

qemu-img create -f qcow2 -o preallocation=falloc $HOME/vms/$HOSTNAME-rootdisk 32768M

Edit: Fix nameserver enforcement in build script.

Tagged with:

Categorised as:

Basic MRTG config

It's a mess, but making things work took some effort, and a lot of copypasting from numerous sources, so I'm recording this here.


WorkDir: /var/www/mrtg
WriteExpires: Yes
Language: english
Title[^]: Traffic Analysis for Yourserver
Options[_]: growright, bits

LoadMIBs: /usr/share/mibs/netsnmp/UCD-SNMP-MIB, /usr/share/mibs/ietf/TCP-MIB, /usr/share/mibs/ietf/UDP-MIB, /usr/share/mibs/ietf/HOST-RESOURCES-MIB

Target[localhost.cpu]:ssCpuRawUser.0&ssCpuRawUser.0:yoursnmpcommunity@localhost+ ssCpuRawSystem.0&ssCpuRawSystem.0:yoursnmpcommunity@localhost+ ssCpuRawNice.0&ssCpuRawNice.0:yoursnmpcommunity@localhost
RouterUptime[localhost.cpu]: yoursnmpcommunity@localhost
MaxBytes[localhost.cpu]: 100
Title[localhost.cpu]:  CPU Load
PageTop[localhost.cpu]: <H1> Active CPU Load %</H1>
Unscaled[localhost.cpu]: ymwd
ShortLegend[localhost.cpu]: %
YLegend[localhost.cpu]: %
Legend1[localhost.cpu]: %
LegendI[localhost.cpu]: Active
Options[localhost.cpu]: growright,nopercent

Target[localhost.mem]: .
PageTop[localhost.mem]: <H1> Free Memory</H1>
Options[localhost.mem]: nopercent,growright,gauge,noo
Title[localhost.mem]:  Free Memory
MaxBytes[localhost.mem]: 1000000
kMG[localhost.mem]: k,M,G,T,P,X
YLegend[localhost.mem]: bytes
ShortLegend[localhost.mem]: bytes
LegendI[localhost.mem]: Free Memory:
Legend1[localhost.mem]: Free memory, not including swap, in bytes

Target[localhost.swap]: memAvailSwap.0&memAvailSwap.0:yoursnmpcommunity@localhost
PageTop[localhost.swap]: <H1> Swap Available</H1>
Options[localhost.swap]: growright,gauge,nopercent
Title[localhost.swap]:  Swap Available
MaxBytes[localhost.swap]: 1073741824
kMG[localhost.swap]: k,M,G,T,P,X
YLegend[localhost.swap]: bytes
ShortLegend[localhost.swap]: bytes
LegendI[localhost.swap]: Swap Available:
Legend1[localhost.swap]: Swap memory available

Target[localhost.rootdisk]: dskPercent.1&dskPercent.1:yoursnmpcommunity@localhost
PageTop[localhost.rootdisk]: <H1> Used Root Disk</H1>
Title[localhost.rootdisk]:  Used Root Disk
MaxBytes[localhost.rootdisk]: 100
Options[localhost.rootdisk]: nopercent,growright,gauge
Unscaled[localhost.rootdisk]: ymwd
ShortLegend[localhost.rootdisk]: %
YLegend[localhost.rootdisk]: %

Target[localhost.eth0]: /
MaxBytes[localhost.eth0]: 12500000
Title[localhost.eth0]:  eth0
PageTop[localhost.eth0]: <h1> eth0</h1>
ShortLegend[localhost.eth0]: b/s
YLegend[localhost.eth0]: b/s

Target[localhost.eth1]: /
MaxBytes[localhost.eth1]: 12500000
Title[localhost.eth1]:  eth1
PageTop[localhost.eth1]: <h1> eth1</h1>
ShortLegend[localhost.eth1]: b/s
YLegend[localhost.eth1]: b/s

Target[localhost.udpin]: udpInDatagrams.0&udpInDatagrams.0:yoursnmpcommunity@localhost
PageTop[localhost.udpin]: <H1> Incoming UDP pkts per minute</H1>
Title[localhost.udpin]:  Incoming UDP pkts per minute
MaxBytes[localhost.udpin]: 1000000
ShortLegend[localhost.udpin]: p/m
YLegend[localhost.udpin]: p/m
LegendI[localhost.udpin]: Incoming
Options[localhost.udpin]: nopercent,growright,perminute

Target[localhost.udpout]: udpOutDatagrams.0&udpOutDatagrams.0:yoursnmpcommunity@localhost
PageTop[localhost.udpout]: <H1> Outgoing UDP pkts per minute</H1>
Title[localhost.udpout]:  Outgoing UDP pkts per minute
MaxBytes[localhost.udpout]: 1000000
ShortLegend[localhost.udpout]: p/m
YLegend[localhost.udpout]: p/m
LegendO[localhost.udpout]: Outgoing
Options[localhost.udpout]: nopercent,growright,perminute

Target[localhost.tcpconns]: tcpCurrEstab.0&tcpCurrEstab.0:yoursnmpcommunity@localhost
Title[localhost.tcpconns]:  TCP Connections
PageTop[localhost.tcpconns]: <H1> TCP Connections</H1>
MaxBytes[localhost.tcpconns]: 10000000000
ShortLegend[localhost.tcpconns]: conns
YLegend[localhost.tcpconns]: conns
LegendI[localhost.tcpconns]: Incoming
LegendO[localhost.tcpconns]: Outgoing
Legend1[localhost.tcpconns]: Established incoming connections
Legend2[localhost.tcpconns]: Established outgoing connections
Options[localhost.tcpconns]: nopercent,gauge,growright

Target[localhost.tcpnewconns]: tcpPassiveOpens.0&tcpActiveOpens.0:yoursnmpcommunity@localhost
Title[localhost.tcpnewconns]:  New TCP Connections
PageTop[localhost.tcpnewconns]: <h1> New TCP Connections / minute</h1>
MaxBytes[localhost.tcpnewconns]: 1000000000
ShortLegend[localhost.tcpnewconns]: conns/min
YLegend[localhost.tcpnewconns]: conns/min
LegendI[localhost.tcpnewconns]: Incoming
LegendO[localhost.tcpnewconns]: Outgoing
Legend1[localhost.tcpnewconns]: New inbound connections
Legend2[localhost.tcpnewconns]: New outbound connections
Options[localhost.tcpnewconns]: growright,nopercent,perminute

Tagged with:

Categorised as:

Running a Django app with Gunicorn and Upstart

Skimmed from here, I mostly just changed the last line that starts Gunicorn from using gunicorn_django to plain gunicorn, as recommended by the Django overlords.


description "Your App"
author "Your Name "

start on (net-device-up and local-filesystems)
stop on shutdown

    export HOME="/root/of/django/app" # i.e. where "" can be found
    export PATH="$PATH:/root/of/django/app/env/bin" # "env" is our virtualenv
    export DJANGO_SETTINGS_MODULE="settings"
    export LANG="en_US.UTF-8"
    cd $HOME
    exec $HOME/env/bin/gunicorn -b -w 1 --log-file /var/log/gunicorn/yourapp.log app
end script

import os, sys

sys.path.insert(0, '/root/of/django/app/')
path = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
if path not in sys.path:

import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()

Tagged with:

Categorised as:

Autossh with Ubuntu Upstart

Like the title says, the point of this post is getting autossh up when Ubuntu boots. Place this in e.g. /etc/init/autossh.conf, after which you will be able to says things like sudo start autossh and sudo stop autossh.

    description "autossh tunnel"
    author "Joni Kähärä "
    start on (local-filesystems and net-device-up IFACE=eth0 and net-device-up IFACE=eth1) # assuming we have multiple interfaces
    stop on runlevel [016]
    respawn limit 5 60
    exec autossh -M 0 -N -R 10000: -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -o "StrictHostKeyChecking=no" -o "BatchMode=yes" -i /home/user/.ssh/id_rsa username@hostname

The “start on” line ensures that autossh won’t start before all network interfaces are up, and “stop on” will stop autossh (if it’s running) on runlevels 0, 1 and 6 (halt, single user and reboot, respectively). The “respawn limit” line will ensure that if autossh goes crazy, it will not be started again. Note that the plain “respawn” line is still needed to actually respawn the process. Of the command line options only the first one (-M 0) is for autossh, the rest are regular ssh options.

  • -M 0 denotes that autossh should not set up it’s own monitoring channel and should instead rely on ssh terminating itself when it decides that the connection’s been lost (see ServerAlive* options below).
  • -N means “Do not execute a remote command”, i.e. just set up the connection and port forward.
  • -R 10000: means that we want TCP port 10000 on the remote host forwarded to port 22 on local host (
  • -o "ServerAliveInterval 60" send “keepalive” messages every 60 seconds
  • -o "ServerAliveCountMax 3" terminate ssh if three consecutive ServerAliveInterval inquiries fail (and thus respawn)
  • -o "StrictHostKeyChecking=no" don’t fail if remote server’s identity changed
  • -o "BatchMode=yes" don’t attempt to use a passphrase if public key login fails
  • -i /home/user/.ssh/id_rsa the private key we’ll use for the tunnel
  • username@hostname connect to this host with this username

Tagged with:

Categorised as:

Amazon DynamoDB basics with Boto

The code assumes that Boto credentials have been set up.

      import boto.dynamodb
      from boto.dynamodb.condition import *
      connection =  boto.dynamodb.connect_to_region('eu-west-1')
      table = connection.get_table('table')
      id = '1'
      timestamp = 1234
      attrs = {
        'key1': 'value1',
        'key2': set(['value2', 'value3'])
      # create
      item = table.new_item(hash_key=id, range_key=timestamp, attrs=attrs)
      # read
      item = table.get_item(hash_key=id)      
      key2 = list(item['key2'])
      # update
      item['key1'] = 'foo'
      item['key3'] = 'bar'
      # query
      table.query(hash_key=id, range_key_condition=LT(1500))
      # scan
      table.scan(scan_filter={'key1': EQ('foo')})
      # delete
      item = table.get_item(hash_key=id)

Tagged with:

Categorised as: