How to change the hostname in Ubuntu

To change hostname in Ubuntu or any Debian variant Linux, modify the /etc/hostname and /etc/hosts.

sudo vi /etc/hostname

Change the old hostname to a new hostname.

sudo vi /etc/hosts

Also, change the oldhostname to a new hostname,

192.168.1.100               newhostname

After done, changing the /etc/hostname and /etc/hosts, you need to restart the hostname service.

sudo /etc/init.d/hostname.sh stop

sudo /etc/init.d/hostname.sh start

And then you log out from the shell and log in back. Once logged in, type

hostname

to check on the changes you have made for the hostname.

Ubuntu auto shutdown due to high CPU temperature

I use a laptop with Ubuntu 8.10 installed at work. While running the some high process, the CPU temperature get really high and its automatically shutdown the system. This thing happen every 2 or 3 days and its really annoying. The syslog showed the following error message:

ACPI: Critical trip point
Critical temperature reached (100 C), shutting down.

I know it is a safety feature, but really, I can’t afford to keep having the system shutdown while my system doing something important. My system fans are working but for whatever reason my CPU temp exceeds the critical threshold of 99C. On some systems you can see what your threshold is within the BIOS and even edit it but not on this one. So what’s a frustrated developer supposed to do? Well, it turns out you can tell you system to ignore the high temp threshold and to just keep on chugging along. NOTE: This isn’t the best advice I ever gave, if you do this then fry your CPU don’t come bitching to me.

sudo vi /etc/modprobe.d/options

Go to the last line of the file and add:
options thermal nocrt=1

Save the file.

Once you have this option set you need to reconfigure the kernel to pick up these changes, enter the following command:

sudo dpkg-reconfigure linux-image-$(uname -r)

This will update your kernel and then tell you to restart when it is done. Once you restart the system, type the following command the verfiy:

cat /proc/acpi/thermal_zone/*/*

It should display something similar like below.

<setting not supported>
<polling disabled>
state:                   ok
temperature:             52 C
critical (S5):           99 C <disabled>

Now your system won’t restart when the critical heat point is passed. Again, don’t blame me if you hurt your machine by doing this.

How to setup headless Sun xVM VirtualBox on Ubuntu server

The steps are not too difficult but I did have to find a few places for information. Search on the forum turn up nothing on this subject so hopefully this HOWTO would be helpful to someone out there.

Note: This is not using the OSE version.

Background:
VirtualBox has a very good GUI running on the host to manage guest OS. However when running a server, we typically do not want to run X on it. Fortunately VirtualBox has commandline tools to manage guest systems. It also provides the VirtualBox Remote Desktop Protocol (VRDP) to allow connection to the guest remotely.

Clarification of terms used:
Host – refers to the machine we are trying to install VirtualBox.
Guest – the VirtualBox guest system that is setup on the host.
Remote – the PC that we are working on to connect to the host via SSH.

This setup was done on a fresh install of Ubuntu Server 8.04 with openssh-server installed.

All the following steps are done by SSH into the host from a remote (I’m using Windows for now).

1. Get required packages
Download the Ubuntu package for VirtualBox from http://www.sun.com/software/products/virtualbox/get.jsp

wget “download link here” -O virtualbox_1.6.2-31466_Ubuntu_hardy_i386.deb

We are using the non-OSE version here.

The manual from http://www.virtualbox.org/wiki/Downloads is also very useful.

2. Installation

sudo dpkg -i virtualbox_1.6.2-31466_Ubuntu_hardy_i386.deb

This will generate a bunch of dependencies. Fix them with

sudo apt-get -f upgrade

3. Decide on user, disk files location

First decide which user you want to run VirtualBox. Add this user to the vboxusers group.

sudo usermod -a -G vboxusers vboxuser

By default VirtualBox creates the directory .VirtualBox on the user home directory and put all the config and disk file there. In my setup, I put the disk files in /var/vbox as I had created a large partition for this purpose.

4. Install a guest OS

You will need an iso for the guest OS install CD. Copy or download it to the host. For example we will just use ubuntu-8.04-server-i386.iso

-create a vm

VBoxManage createvm -name ubuntu -register

-config vm

VBoxManage modifyvm ubuntu -memory “256MB” -acpi on -boot1 dvd -nic1 nat

-create a disk

VBoxManage createvdi -filename “/var/vbox/ubuntu.vdi” -size 5000 -register

-add disk to vm

VBoxManage modifyvm ubuntu -hda “/var/vbox/ubuntu.vdi”

-register an install iso

VBoxManage registerimage dvd /var/vbox/ubuntu-8.04-server-i38.iso

-mount iso on vm

VBoxManage modifyvm ubuntu -dvd /var/vbox/ubuntu-8.04-server-i38.iso

-start the vm with port

VBoxHeadless -startvm ubuntu -p 3389 &

If you are running just 1 guest, the -p 3389 is optional. For more than 1 guest, it has to listen to different port.

5. Connect from remote

Since my desktop is still Windows, I use Remote Desktop Connection. (On XP, Start>All Programs>Accessories>Communications)

For Mac, use http://www.microsoft.com/mac/products/remote-desktop/
For Ubuntu, look at http://ubuntuforums.org/showthread.php?t=824710

Just fill in the IP of your host (or IP:port if not the default) and you should see the Ubuntu installation waiting for you.

Other useful commands:

VBoxManage controlvm ubuntu poweroff
VBoxManage controlvm ubuntu reset

Getting Ubuntu Server to run in VirtualBox

After installation and restarting, you may find that the boot up hang with this error

This kernel requires the following features not present on the CPU: 0:6

To fix this, do the following:

1. Reset the guest
2. Hit F12 to choose to boot from the CD. (It goes by pretty quickly, reset again if you miss it.)
3. Select Rescue a broken system
4. After going through the install screens you will get a command prompt. Select to run it on the root system.
5. Install the virtual linux-virtual kernel

apt-get install linux-virtual

6. Reboot and this should fix the restart.

Upgrading kernel
If the kernel on the host is upgraded, the VirtualBox kernel module need to be re-compiled. Do the following steps:

1. apt-get install make gcc linux-headers-2.6.24-19-server (other kernel header, check uname -a)
2. /etc/init.d/vboxdrv setup

It should recompile the VirtualBox module and everything should be working again.

[ Source: kcnnc from Ubuntu Forum ]