Note: This is a copy of the original guide by Mattb81. I have made this copy purely so that it can be maintained, because Matt is not currently active in this forum. All credit for writing it belongs to Matt, so if you find it helps you please click on this link to the original thread and Thank Matt, not me.
Now over to Matt :
As many people are saying there isn't a guide for this and I found it quite easy, I thought I'd write a simple one. At the moment I don't have the time to make it too pretty or repeat things which SURoot has already done in other guides, but over time I will edit and improve it.
Revolutionary is not the same as Unrevoked. Revolutionary is more like the successor to Alpharev than the successor to Unrevoked, as Unrevoked roots your phone, while Revolutionary will S-OFF your phone. You then have to root it by running a root zip file in recovery mode.
It's just another way of getting to the end goal of having more options of what you can do with your phone.
Revolutionary will not work for every Desire (currently), but it will work for certain HBoots and is the only way for people who have the "official" HTC Gingerbread Android. Froyo users can also S-OFF and root this way too if you have the right hboot (I did, because Unrevoked didn't work).
Almost everyone should be able to get rooted using either this guide or the Unrevoked guide.
I'm assuming the goal is to root your phone. If you just want to S-OFF and have already rooted, you can ignore most of the sections as you've probably already done them. You can probably just run the Revolutionary software and follow the prompts (Section 5).
For everyone else, follow this:
-------------------------------------------------------------------------------------------
SETUP / PREP
1) Firstly, sort out your drivers so your PC speaks with your phone: (note usb debugging should always be on). Skip this step if you are using Linux instead of Windows.
a) Download HTC Sync and uninstall (this leaves the drivers behind but not the program which can interfere with things, you can reinstall it after your rooted)
b) Download and install HBoot driver (see Unrevoked guide for the download link and guide)
2) Choose your recovery: (Updated 09/07/2012 - Hadron)
Revolutionary will, if you let it, install a custom recovery for you. However, our experience is that there are better (i.e. more stable) recoveries for the Desire.
The current recommendation in this forum is 4Ext Touch recovery. The normal way of installing this is through an app once you are S-Off and rooted, as described in that thread. However, the first post of the thread also includes direct download links for GSM and CDMA versions of the recovery (just look for the phrase "direct download" in that post). Choose the correct version for your phone, download to your computer, unzip the package and you will find a recovery .img file which you can flash in Step 6 below. There is also an md5 code so that you can check that you have a good download.
Once you have finished rooting you can install the 4Ext app to keep the recovery updated.
If have a GSM device and would prefer one of the older, non-touch recoveries, then you need to check what sort of device you have in order to determine which is compatible:
a) Find out your PVT version: Boot into HBoot (from off, hold vol-down and press power), make note of HBoot version. If PTV4, follow (b) to (d). If not, go to (e)
b) Download Terminal Emulator from the market and open it
c) Type "cat /proc/mtd" and press enter. It will return results of either 20000 or 40000
d) If 40,000 - download Amon-Ra 2.0.1 Recovery (see below section (e)) and store it in a easy to find and access place on your PC (ie C:/ )
e) if 20000 or not ptv4, download your choice of recovery below, either will work.
Amon-Ra 2.0.1 or ClockWorkMod 2.5.0.7
NOTE: Clockworkmod 2.5.0.7 asks for a username and pw to download. This can be found in the Useful Downloads thread, usually near the last page.
3) Read the [FAQ] ADB and FASTBOOT for Windows
You don't have to necessarily understand it (I didn't until I used it), but just follow the set up instructions.
4) On the Revolutionary page read everything and download the following:
a) Revolutionary zip - save to PC. They will ask for info (currently) on your phone to get a beta key.
b) Root file - place this on your SD card. Superuser-3.0.7-efgh-signed.zip (there's an older version at: Goo.im Downloads - Downloading su-2.3.6.3-efgh-signed.zip). The revolutionary site also has a link to this in their documentation.
I can't express how important it is that you understand what this program does and what you still need to do afterwards. Read everything on the site, especially the FAQ
Now you're ready to go.
S-OFF PROCESS
5) Run Revolutionary (unzip and run) and follow prompts. Say no to installing their recovery.
Congratulations, you should be S-OFF now. You can check by booting to Hboot and seeing if you have a nice pink "Revolutionary" label above your HBoot info.
ADDING CUSTOM RECOVERY
6) it's time to install your recovery file.
a) Boot into fastboot mode (from off, volume-up and power or volume-down and power then cycle to fastboot option)
b) Connect phone to PC through USB. You should see "FASTBOOT USB" on your phones screen.
c) Open CMD (Start > Run > type "cmd" and press enter)
d) Type "fastboot flash recovery c:\your recovery file name" where c:\your recovery file name is the exact location and name of the recovery file you downloaded.
You should now have a S-OFF phone with a custom recovery.
If you chose 4Ext (which is my preference), check the "Addendum" at the end of this guide. Do not format system even if it tells you to!
ROOTING PROCESS
7) Now for rooting:
a) Boot into Hboot (from off, hold vol-down and power) and choose "Recovery" from the menu.
Optional: you may choose to take a backup while in recovery, before the next step. This is insurance - although the risk is low, if anything does go wrong with the next bit you can restore the backup from recovery and the phone is working again. Making a recovery backup ("nandroid") before flashing anything is a good habit to get into.
b) Choose "flash zip from SD card" or similar from Recovery menu (use trackpad to navigate)
c) Choose the Root file you downloaded to your SD card in step 4b.
d) Wait till it says it's done, then choose to reboot.
Congratulations, you're S-OFF and Rooted!
Addendum
Sometimes a newly-installed 4Ext recovery gets confused and claims it can't read /system, and asks you to format system. Don't do this, as it will erase your ROM. Reboot recovery instead - that usually sorts it out.
Now over to Matt :
As many people are saying there isn't a guide for this and I found it quite easy, I thought I'd write a simple one. At the moment I don't have the time to make it too pretty or repeat things which SURoot has already done in other guides, but over time I will edit and improve it.
Revolutionary is not the same as Unrevoked. Revolutionary is more like the successor to Alpharev than the successor to Unrevoked, as Unrevoked roots your phone, while Revolutionary will S-OFF your phone. You then have to root it by running a root zip file in recovery mode.
It's just another way of getting to the end goal of having more options of what you can do with your phone.
Revolutionary will not work for every Desire (currently), but it will work for certain HBoots and is the only way for people who have the "official" HTC Gingerbread Android. Froyo users can also S-OFF and root this way too if you have the right hboot (I did, because Unrevoked didn't work).
Almost everyone should be able to get rooted using either this guide or the Unrevoked guide.
I'm assuming the goal is to root your phone. If you just want to S-OFF and have already rooted, you can ignore most of the sections as you've probably already done them. You can probably just run the Revolutionary software and follow the prompts (Section 5).
For everyone else, follow this:
-------------------------------------------------------------------------------------------
SETUP / PREP
1) Firstly, sort out your drivers so your PC speaks with your phone: (note usb debugging should always be on). Skip this step if you are using Linux instead of Windows.
a) Download HTC Sync and uninstall (this leaves the drivers behind but not the program which can interfere with things, you can reinstall it after your rooted)
b) Download and install HBoot driver (see Unrevoked guide for the download link and guide)
2) Choose your recovery: (Updated 09/07/2012 - Hadron)
Revolutionary will, if you let it, install a custom recovery for you. However, our experience is that there are better (i.e. more stable) recoveries for the Desire.
The current recommendation in this forum is 4Ext Touch recovery. The normal way of installing this is through an app once you are S-Off and rooted, as described in that thread. However, the first post of the thread also includes direct download links for GSM and CDMA versions of the recovery (just look for the phrase "direct download" in that post). Choose the correct version for your phone, download to your computer, unzip the package and you will find a recovery .img file which you can flash in Step 6 below. There is also an md5 code so that you can check that you have a good download.
Once you have finished rooting you can install the 4Ext app to keep the recovery updated.
If have a GSM device and would prefer one of the older, non-touch recoveries, then you need to check what sort of device you have in order to determine which is compatible:
a) Find out your PVT version: Boot into HBoot (from off, hold vol-down and press power), make note of HBoot version. If PTV4, follow (b) to (d). If not, go to (e)
b) Download Terminal Emulator from the market and open it
c) Type "cat /proc/mtd" and press enter. It will return results of either 20000 or 40000
d) If 40,000 - download Amon-Ra 2.0.1 Recovery (see below section (e)) and store it in a easy to find and access place on your PC (ie C:/ )
e) if 20000 or not ptv4, download your choice of recovery below, either will work.
Amon-Ra 2.0.1 or ClockWorkMod 2.5.0.7
NOTE: Clockworkmod 2.5.0.7 asks for a username and pw to download. This can be found in the Useful Downloads thread, usually near the last page.
3) Read the [FAQ] ADB and FASTBOOT for Windows
You don't have to necessarily understand it (I didn't until I used it), but just follow the set up instructions.
4) On the Revolutionary page read everything and download the following:
a) Revolutionary zip - save to PC. They will ask for info (currently) on your phone to get a beta key.
b) Root file - place this on your SD card. Superuser-3.0.7-efgh-signed.zip (there's an older version at: Goo.im Downloads - Downloading su-2.3.6.3-efgh-signed.zip). The revolutionary site also has a link to this in their documentation.
I can't express how important it is that you understand what this program does and what you still need to do afterwards. Read everything on the site, especially the FAQ
Now you're ready to go.
S-OFF PROCESS
5) Run Revolutionary (unzip and run) and follow prompts. Say no to installing their recovery.
Congratulations, you should be S-OFF now. You can check by booting to Hboot and seeing if you have a nice pink "Revolutionary" label above your HBoot info.
ADDING CUSTOM RECOVERY
6) it's time to install your recovery file.
a) Boot into fastboot mode (from off, volume-up and power or volume-down and power then cycle to fastboot option)
b) Connect phone to PC through USB. You should see "FASTBOOT USB" on your phones screen.
c) Open CMD (Start > Run > type "cmd" and press enter)
d) Type "fastboot flash recovery c:\your recovery file name" where c:\your recovery file name is the exact location and name of the recovery file you downloaded.
You should now have a S-OFF phone with a custom recovery.
If you chose 4Ext (which is my preference), check the "Addendum" at the end of this guide. Do not format system even if it tells you to!
ROOTING PROCESS
7) Now for rooting:
a) Boot into Hboot (from off, hold vol-down and power) and choose "Recovery" from the menu.
Optional: you may choose to take a backup while in recovery, before the next step. This is insurance - although the risk is low, if anything does go wrong with the next bit you can restore the backup from recovery and the phone is working again. Making a recovery backup ("nandroid") before flashing anything is a good habit to get into.
b) Choose "flash zip from SD card" or similar from Recovery menu (use trackpad to navigate)
c) Choose the Root file you downloaded to your SD card in step 4b.
d) Wait till it says it's done, then choose to reboot.
Congratulations, you're S-OFF and Rooted!
Addendum
Sometimes a newly-installed 4Ext recovery gets confused and claims it can't read /system, and asks you to format system. Don't do this, as it will erase your ROM. Reboot recovery instead - that usually sorts it out.