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Check in the root section or the guide in my sig.
checked...is it difficult?

u didn`t checked if you ask this question...
The preferred rooting method round these parts is CF-Root.
hi!Not sure if z4 works on the gs2. Anyway the you guide steslatt mentioned is the easiest way.
[15.12.2011][CF-Root 5.1] KE*,KF*,KG*,KH*,KI*, KJ1/2/3, KK2/5, KP1/2 - su+bb+CWM4/5 - xda-developers
1. On your phone go to settings, menu, about phone and write down your kernel name.
2. Download odin from the link (first post) and unzip with your pc and instal
3. Download the cfroot kernel from the link which matches what you wrote down and unzip it with your pc. You will now have a .tar or .tar.md5 file
4. I assumed you already have the kies drivers installed on your pc. If not download them from samsung.
5. Make sure all kies programs are closed and open odin.
6. Tick the pda box, then press next to it and select the .tar/.tar.md5 file
7. With your phone turned off press power, volume down and menu together and you will see a screen asking if you want to continue into download mode. Press up to say yes.
8. Attach your phone to your pc with your usb cable
9. Press start
10. Enjoy
Seriously its easier than I just made it sound
i dowloaded cfroot,when i unzip\unrar it i have only 1 file called "zImage", what should i do?

samsung galaxy s2 screen appear but os doesn't load...why?what do you mean by "blocked"?
Sounds to me your in a boot loop.
Are you sure you flashed the correct file and did you follow the instructions to the letter?
I would try downloading and flashing it again.
Rooting guide (Chainfire)
To make sure your using Odin correctly, follow the guide on here This is for flashing firmware (which you dont want) but it has a better guide on how to use Odin, so just replace the PDA file with the one in the rooting guide (first link)
downloaded,then?
<ID:0/014> Added!!
<ID:0/014> Odin v.3 engine (ID:14)..
<ID:0/014> File analysis..
<ID:0/014> SetupConnection..
<ID:0/014> Initialzation..
<ID:0/014> Get PIT for mapping..
<ID:0/014> Firmware update start..
<ID:0/014> zImage
it takes a lot here...why?
