How to change the default runlevel on Ubuntu

 On Redhat you would simply look for the file /etc/inittab and locate the line that says:

# The default runlevel.

Simply replace the 3 with 2 or 4 or 5 depending what you wanna do in order to change the default runlevel.

On Ubuntu starting from some version around 6sh… whatever, no one is running that anymore anyway and those who do run it don’t need to change that. At the time I am writing this the current LTS is 10.04 and the current testing release is 10.10
So here is how to do it.

send a mail in command line in Ubuntu

 By default the binary "mail" is not installed on Ubuntu. At least it’s not on my brand new Ubuntu 10.10.
You need to setup the package mailutils.

apt-get install mailutils

Then you can send an email using the command line:

ls | mail

How to follow the progress of a gzip or tar

First you need pv, Pipe Viewer

[bash]$ apt-get install pv
[bash]$ SIZE=`du -sk some-folder | cut -f 1`
[bash]$ tar cvf - some-folder | pv -p -s ${SIZE}k | gzip -c > folder.tar.bz2

extract one file from a tar.gz

You can simply use the following syntax:

[root@blub ~]# tar tzvf mytar.tar.gz
That will show you the list of files in the tar. t means test
[root@blub ~]# tar tzvf mytar.tar.gz myfile.txt
 -rw-rw-r-- scm/scm 373093723 2010-09-17 17:58:21 myfile.txt
You can do the same with a target file and test that one specific file really belong to a tar.gz

Finally you can extract that single file.

Make a virtual machine out of a G4L archive

So I took a backup of a disk using G4L.
Let’s import it into a virtual machine on a RedHat running Xen.

virt-install --import --file <myfile> --prompt

answer the few questions.
Choose "Fully Virtualized".
Turn the SELinux into permissive mode in order to configure the network. This is a known bug and it looks like it’s not corrected yet.

setenforce Permissive

Once the import is done your virtual machine should pop and boot properly.