bash

Bash: tail: Remove first N lines from file

 in Bash / GNU/Linux / HowTos  tagged bash / GNU/Linux / howtos / line / lines / tail by 

tail -n +$N inputFile > outputFile

Where $N is the number of the line which you want to start printing from.
For example if you want to delete only the first line / start printing from the second line you must issue the following:

tail -n +2 inputFile > outputFile

Ubuntu 11.10 (Oneiric Ocelot): Installing KVM 2

 in Applications / HowTos / Virtualization  tagged applications / bash / GNU/Linux / howtos / KVM / virtualization by

Without any additional comments, we managed to install KVM over a fresh installation of Ubuntu 11.10 (Oneiric Ocelot).

To do this we installed the following packages from the repositories and added our user to the libvirtd group.

We called kvm-ok to make sure that our hardware supports KVM properly and thus having better performance.
Installation Commands:

sudo apt-get install kvm libvirt-bin
sudo adduser $USER libvirtd
sudo apt-get install virt-viewer
sudo apt-get install python-vm-builder
sudo apt-get install bridge-utils
sudo apt-get install virtinst #for cloning

After these we created a virtual machine with the following command:

sudo vmbuilder kvm ubuntu --suite oneiric --flavour virtual --arch amd64 --mem 1024 --cpus 2 -o --libvirt qemu:///system --ip 192.168.0.100 --hostname uranus --part vmbuilder.partition --user userName --name MyName MySurname --pass myPassword --addpkg unattended-upgrades --addpkg acpid --addpkg nano

where in general, what it does is, create an Ubuntu Oneiric Ocelot JeOS virtual machine that has an AMD64 architecture, 1GB of RAM, 2 Virtual CPUs, it’s name is uranus, has a user with the username userName, has pre-installed some applications like nano and enabled automatic updates for the system.

How to setup DNS service for DHCP-enabled KVM guests

 in Applications / HowTos / Virtualization  tagged /etc/resolv.conf / bash / DHCP / DNS / GNU/Linux / howtos / KVM / nameserver / ubuntu by

So you’ve set up KVM on your machine and you have installed a few guests to run on top, now it’s the time to access them.

Since KVM can run without a GUI, you might want to control these guests from the command line. But, how can you do it if you do not know the IP of the guests?

You can either connect to the guest using virt-viewer:

virt-viewer -c qemu:///system $MACHINE &

which requires more bandwidth since it will open up a VNC session.

Or, use ssh to connect using the guest’s name, like this:

ssh $MACHINE

which doesn’t require that you know the IP beforehand.

To achieve this, access guest machines using their hostname only, you can do the following: Edit /etc/resolv.conf and add the line nameserver 192.168.122.1 right after the search entries .

Your file should look something like this afterwards:
domain in.bytefreaks.net
search in.bytefreaks.net
nameserver 192.168.122.1
nameserver 194.44.13.20
nameserver 194.44.13.58
nameserver 194.44.13.11

Then you are ready to go! No restarts needed no extra steps.

NOTES:

  • After restarting (and some times periodically), the /etc/resolv.conf file will return to its original form because it is updating each time you restart the host machine from data it gets via the network DHCP server.
  • For this tutorial to work as is, your host machine needs to have the virtual IP 192.168.122.1 (the default IP of your host in libvirt — NOT THE IP of eth0, it’s a totally different thing). If you have a different libvirt IP use that one in the /etc/resolv.conf file.
  • Use your host’s IP as your first nameserver in /etc/resolv.conf to achieve name resolution for your guests.

How to change hostname (computer name) in Ubuntu (or Ubuntu Server)

 in Bash / GNU/Linux / HowTos  tagged /etc/hostname / bash / GNU/Linux / hostname / howtos by

If you do not have Unity/Gnome/KDE/or some other window manager, to do this you need to be familiar with a command line text editor like vi/emacs/nano.

To change your hostname simply edit /etc/hostname and restart the machine.

The /etc/hostname file should only contain the actual hostname, which makes editing it quite simple since you will just replace the hostname in the file with the one you want to assign.

NOTE: Elevated privileges are required, only administrators can edit this file.