1.  Ubuntu 10.10 iPhone Toolchain 4

2.  Install the following packages

sudo apt-get update
sudo apt-get install bison flex build-essential wget patch
sudo apt-get install git autoconf gawk libssl-dev uuid-dev
sudo apt-get install clang

3.  Create /toolchain4
    sudo mkdir -p /toolchain4
    sudo chown -R <yourusername>:<yourusername> /toolchain4

4.  Put iPhoneOS4.2.sdk.tgz to /toolchain4/sdks/
    
    or build xar
    sudo apt-get install libxml2-dev
    ./toolchain.sh xar
    then put iPhoneSDK4_2.pkg to /toolchain4/sdks/

5.  Build headers tools and gcc 
    cd /toolchain4
    ./toolchain.sh buildsys
    ./toolchain.sh cctools
    ./toolchain.sh llvmgcc
    ./toolchain.sh ldid

6.  Install as_driver
    cd /toolchain4/as_driver
    make
    cd /usr/bin
    sudo mv as i686-linux-gnu-as
    sudo cp -p /toolchain4/as_driver/as_driver as
    sudo ln -s /toolchain4/pre/bin/arm-apple-darwin9-as .
    sudo ln -s /toolchain4/pre/bin/arm-apple-darwin9-ld .

7.  Test iOS4 sample code
    cd /toolchain4/Projects/LocalPush
    make
    make dist
    (LocalPush.app & LocalPush.ipa will be in build/4.0/ folder)