I have bought a Samsung Galaxy S Android phone some time ago. One of the first thing that you try to do with such a phone is to switch to some alternate firmware (the coined term is “ROM”), like CyanogenMod. Flashing a firmware is a whole new universe. You are told about a lot of proprietary tools, you need to download a lot of things from MegaUpload and friends and nobody really explains what’s going on under the hood. I was a bit lost at first.

I will not provide a step-by-step guide since I cannot afford to stay up-to-date. Such a guide is usually posted on some forum. It assumes you are running Windows and provides appropriate download links. You must follow it (and check that it is recent enough). I will just provide you some background to understand those guides.

Android firmwares§

There are several Android firmwares. Most of them are specific to a given phone (or its close variations). They can be sorted in three categories:

  1. Official firmwares from the phone manufacturer include a kernel with appropriate drivers and, usually, a customized interface (HTC Sense for HTC, TouchWiz for Samsung). Some manufacturers will lag a lot behind Android schedule and you may not get all the new shiny features.
  2. Modified firmwares are built from the official firmwares. They usually add a lot of hacks on top of the original firmware, remove some cruft but are still closely related to the official firmware.
  3. Firmwares built from Android Open Source Project (the open source version of Android) do not share nothing with the official firmware except some bits related to the kernel (drivers, hacks).

Darky ROM§

Darky ROM is a modified firmware. It takes the original firmware from Samsung, adds a custom kernel (based on the source of the official kernel), adds a lot of hacks, some additional applications and removes some unwanted cruft. This is a very nice firmware which is quite snappy. This is a drop-in replacement for the default firmware: you will only get improvements.

The latest version is 10.1 and there is a neat guide on how to install it.


CyanogenMod is a firmware built from AOSP. It supports several devices and provide an unified firmware on all of them. Support for the Samsung Galaxy S is recent and is not present in the stable build. However, some RC build is now available. Be sure to read the FAQ (most notably the part saying that you need to install from Froyo 2.2 because the bootloader provided by Samsung with Gingerbread 2.3 is not compatible). You can also grab some information from the wiki.

The major drawback of using this firmware instead of going for a modified firmware like Darky ROM is that the battery life may suck. I now need to charge my phone every day instead of once every two days. On the plus side, you get a very clean firmware with a lot of features and almost no cruft. For example, the notification bar can be customized and OpenVPN is available out of the box.

UPDATED: After a few weeks, the battery life is similar to what the original firmware provides. Maybe it was just a calibration problem.

Moreover, almost everything is open source (if you don’t install Google apps). You can see this firmware as an open source distribution for your phone. There is no need to download random files linked from a random forum to make it work. There is no package manager, though. Despite the bad battery life, I prefer this firmware.


Before trying to flash a new firmware, there are some tools that you need to have. Note that you don’t need root access to flash a new firmware.

Download & recovery mode§

Before trying to install any firmware, you must check that your phone can access download and recovery modes. The download mode allows you to flash any new firmware, even if the current firmware does not boot at all. As long as this mode is available, there is very little chance that you brick your phone. To access those modes, you need to use the “three-button combo”. Here are the steps (your phone should not be plugged):

  1. Power off the phone (wait for the phone to vibrate).
  2. Hold the “Volume down” button for download mode. Hold the “Volume up” button for recovery mode.
  3. Hold the “Home” button.
  4. Hold the “Power” button. The phone will start.
  5. Once you have the Samsung logo displayed on the screen, release the “Power” button.
  6. Only release the two other buttons when you enter the recovery mode or download mode. The recovery mode displays a menu. The download mode displays a big yellow Android logo.

If after ten tries, you are unable to access those modes, maybe they have been disabled. Keep reading, there is a solution.


Heimdall is a tool to flash a new firmware to your phone. This is not a mandatory tool but you will have to use it if something goes wrong. Most guides will tell you to use Odin. It is a leaked Samsung tool running on Windows only. You can use Heimdall instead.

$ git clone https://github.com/Benjamin-Dobell/Heimdall.git
Cloning into Heimdall...
remote: Counting objects: 423, done.
remote: Compressing objects: 100% (271/271), done.
remote: Total 423 (delta 220), reused 332 (delta 138)
Receiving objects: 100% (423/423), 5.91 MiB | 962 KiB/s, done.
Resolving deltas: 100% (220/220), done.
$ cd Heimdall/heimdall
$ sudo apt-get install libusb-1.0-0-dev
$ ./configure && make
$ sudo cp 60-heimdall-galaxy-s.rules /etc/udev/rules.d
$ sudo /etc/init.d/udev reload

You need to use this tool while in download mode. You can test it, while in download mode, with:

$ ./heimdall print-pit

This will display the partition table of your phone. This is enlightening to know what it contains:

  • IBL+PBL is the boot loader, be extra careful with it;
  • PIT is the partition table;
  • EFS contains some important data like IEMEI, be extra careful with it;
  • SBL is the second boot loader;
  • SBL2 is the backup of the second boot loader;
  • PARAM contains some images used as various stage of the boot process;
  • KERNEL is the kernel;
  • RECOVERY is the backup of the kernel;
  • FACTORYFS contains /system file system which is some kind of root file system;
  • DBDATA contains /data file system which is the database to store application parameters;
  • CACHE contains /cache file system which contains the Dalvik cache;
  • MODEM contains the firmware for the modem.

As we will see, Heimdall is able to flash any of those partitions with flash subcommand.


adb stands for Android Debug Bridge. Among other things, this tool allow you to drive your phone through the USB connection. You can get a shell, reboot into download or recovery mode, push files to your Android device, etc.

To get this tool, you need to download the full Android SDK.

$ tar zxvf ~/download/android-sdk_r11-linux_x86.tgz
$ cd android-sdk-linux_x86
$ tools/android update sdk
[select Android SDK Platform-tools]
$ platform-tools/adb shell
# uname -a
Linux localhost #Dark_Core_2.4 PREEMPT Mon May 16 15:02:38 EEST 2011 armv7l GNU/Linux

The important commands are:

  • shell to get a shell on the device;
  • reboot recovery to reboot in recovery mode;
  • reboot download to reboot in download mode;
  • push to put a file on the phone;
  • pull to retrieve a file;
  • install to install an application from its APK;
  • logcat to see the logs and what happens, very useful!

Restore download mode§

If your phone is missing download mode, you can recover it with the help of adb and heimdall. You need to grab some official firmware and extract boot.bin and Sbl.bin from it.

$ adb reboot download
$ heimdall flash --primary-boot ~/download/boot.bin --secondary-boot ~/download/Sbl.bin

Be extra careful here. You may brick your phone. Double check that you grab the correct files and that they are really for your phone (there exists some variants). It worked for me.

Installing a new firmware§

While you can switch from one firmware to another without losing your data, it is better to wipe your system and your data before switching firmware. This means that you will lose all your applications and the data inside them (list of contacts, SMS, preferences). However, nothing will ever modify your data in the internal SD card or in the external SD card (which are both inside the phone). They usually contains your music and your photos.

There are two ways to install a firmware:

  1. via Heimdall, or
  2. using the recovery.


When a guide tells you to use Odin, you can use Heimdall instead. Odin takes a TAR file. You should untar it and uses its content with Heimdall. For example:

$ ./heimdall flash --repartition --pit s1_odin_20100512.pit \
>                  --factoryfs factoryfs.rfs \
>                  --cache cache.rfs --dbdata dbdata.rfs \
>                  --param param.lfs --modem modem.bin \
>                  --kernel zImage --secondary-boot Sbl.bin 
Claiming interface again...   Success
Setting up interface...   Success
Beginning session...
Handshaking with Loke...   Success

Uploading PIT
PIT upload successful
Uploading SBL
SBL upload successful
Uploading KERNEL
KERNEL upload successful
Uploading MODEM
MODEM upload successful
Uploading PARAM
PARAM upload successful
FACTORYFS upload successful
Uploading DBDATAFS
DBDATAFS upload successful
Uploading CACHE
CACHE upload successful
Ending session...
Rebooting device...

You may be interested to update your modem using Heimdall. This is usually independent of the firmware you want to use. Also, no need to provide a PIT file if you don’t want to repartition. Heimdall can read the current one and flash only one of the partitions.

Recovery mode§

The base recovery shipped with the Samsung Galaxy S does not have a lot of options. Moreover, it may be locked and will accept to install only signed firmwares. Most firmwares come with ClockWorkMod, a more advanced recovery. Once you get it, you will be able to use any ZIP file to install a new firmware.

My advice is to try to get ClockWorkMod as soon as possible. If you are root, you can install ROM Manager that will install it for you. If you are not root, most custom firmwares will provide ClockWorkMod. Therefore, you can just install a custom firmware with Heimdall. There exists special firmwares just for this, like EZbase. If you want to install CyanogenMod, be sure to download a Froyo firmware, not a Gingerbread one.

Keep in mind that the recovery is located inside the kernel. It is not self-contained in the bootloader (unlike download mode). If you don’t want to flash a whole firmware (and lose everything on your phone) just to get the recovery, you can just flash the kernel.

The ClockWorkMod recovery comes with an utility to backup your whole phone. This way, you can easily restore your previous firmware if you don’t like the current one. This is what is called a Nandroid backup.


A lot of guides will tell you to enable or disable lagfix. Samsung shipped the Galaxy S with some crappy filesystem called RFS (which is some kind of “enhanced” FAT). It is slow and seems responsible for some lags that may happen on the interface. A lagfix is a way to replace this filesystem by something better, like EXT4 or YAFFS2. The process is pretty straighforward and consist to backup all the partition to the SD card, reformat it with another filesystem and restore the backup.

The lagfix may be applied automatically with some firmware (like CyanogenMod) or you may request it in the recovery mode (most modified firmwares work this way). In this case, it will be applied automatically on the next boot. You should disable it before installing another firmware with the recovery mode (no need if you install it with Heimdall).


You can find many free (as in free speech) applications for Android. Unfortunately, Android Market does not allow to use this criteria as a filter. F-Droid is an alternate market featuring only FOSS applications.

Here is a short selection of free applications:

  • ADW.Launcher is a home replacement app. It is very configurable and themable.
  • K-9 Mail is a very nice email client.
  • Xabber is a XMPP/Jabber client.
  • ConnectBot is an SSH client (as well as a terminal).
  • DroidWall is an application firewall (using Netfilter). It lets you select which application can access to Internet depending on your connection (wifi or 3G).
  • Barcode Scanner decodes 1D/2D barcode including QR codes.
  • OsmAnd is a replacement for Google Maps using OpenStreetMap. The free version on Android Market is out-dated. Buy the “plus” version or download it throught F-Droid.

Another must-have application is Titanium Backup which allows you to backup any application with data. Unfortunately, this is not a free (as in free speech) application.