rename and shorten many files with bash

Bash supports a surprising number of string manipulation functions.

For example if you want to get rid of the beginning of the name of a file or a folder on many files at a time you could do the following:

 
bash> ls
mylongfile1
mylongfile2
mylongfile3
mylongfile4
mylongfile5
mylongfile6
mylongfile7
 
bash> for i in *
> do
> mv $i ${i:6}
> done
bash> ls
file1
file2
file3
file4
file5
file6
file7
So to extract the end of a variable after a NUMBER of characters you just need to specify ${variable:NUMBER}
 

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.
id:3:initdefault:

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.