• Introducing XDA Computing: Discussion zones for Hardware, Software, and more!    Check it out!

[INFO] ANDROID DEVICE PARTITIONS and FILESYSTEMS

Search This thread

mirfatif

Senior Member
Oct 18, 2016
659
419
t.me
NOTE:
I'm not a developer or something even near to that. I'm a newbie and will be, seems so. All information provided here is copied and compiled from different internet sources like this and many others.
This information is according to best of my knowledge and comprehension and is just for curious souls like me who want to understand things in quite simple words. It might be wrong and I will open-heartedly welcome any correction or addition from anyone.
I'm not responsible for any harm to you or your device resulting from this.


1. PARTITION TABLE

The Phone's Internal Memory (eMMC or UFS; not the SD card) is solid-state (flash) memory, aka NAND. Raw NAND, as it's called, is basically a pure flash memory dependent on CPU to control it. But in order to use flash memory just like a traditional hard drive (block device), NAND is equipped with an (embedded multimedia) micro-controller. It's called eMMC.

eMMC can be partitioned much like a hard drive on PC. PC's have traditionally been partitioned with BIOS compatible Master Boot Record (MBR) scheme in which first sector of disk contains the details of partitions called Partition Table. Limited size of boot sector (512 bytes) puts a limitation of at maximum 4 (primary) partitions listed in MBR. Extended partition has been used for 4+ partitions.

GUID Partition Table (GPT) was introduced with UEFI booting system which isn't dependent on first boot sector and hence may contain up to 128 partitions. GPT also does CRC check, has backup GPT, identifies partitions by GUID and partitions have a label.

Android devices use GPT. We can view and manipulate GPT using Linux tools such as parted and gdisk while fdisk is the traditional tool for MBR partitions.
To view partition table on internal memory:
Code:
~# parted /dev/block/mmcblk0
(parted) p free

~# gdisk -l /dev/block/mmcblk0

(The external SD Card can also be partitioned to include a section dedicated to storing user apps (like Link2SD does) or to create partitions for secondary or tertiary OS on Android device using some multiboot kernel and recovery system). Even we can put whole OS/ROM on an SD card.

2. BRIEF INTRO
Contents of Android partitions can be partially or completely modified by flashing an image (filesystem .img or executable binary or a flashable zip) to them. But we never need to modify most of them and whatever manufacturer wrote on them, resides there unmodified (read-only) for the whole of device life. A user uses only one partition /data to save personal data like photos, music etc. All the other are for device to run. There are typically in the range of 50 partitions on an Android device but only a few partitions are modified for the purpose of adding new features or upgrading the device. A custom ROM or minor upgrade is also limited to modify /boot, /system and /data partitions usually. Most of the partitions are almost intact, containing bootloaders, firmwares, settings etc. Here is a "summarized" detail to these partitions which matter to a common but interested user.
On most devices /system and /data are larger partitions (on some devices /custom or a similar partition too) covering almost 90% of eMMC. All others are smaller ones of a few KB's or MB's.

3. SoC / CHIPSET / PROCESSORS RELATED PARTITIONS
SoC is the first component when we start a PC or Mobile phone which initialzes hardware and processors and loads bootloaders in memory to bootstrap OS. It's an integrated chip containing multiple things e.g. CPU, GPU, modem, wifi etc. It varies for device manufacturers and SoC vendors (chipset plus processor).
Some partitions are specific to SoC, most of them are closed-source executable binary blobs (like aboot, sbl, rpm, tz, cmnlib, devcfg, keymaster, lksecapp and others on a Qualcomm device), loaded step-by-step by bootloaders.

MODEM or RADIO - the phone's radio
Also called baseband, it is responsible for signals and on older devices may control wifi, bluetooth, and GPS (on most newer devices, these are handled by the kernel and ROM). Upgrades are country dependent and may improve or diminish battery performance, network signal strength, and roaming capability. It is also sometimes required to have a minimum Baseband version to use a ROM so that the RIL will play nice with the Baseband.
Modem firmware is a mini-OS for the cellular radio chip which has its own processor. Firmware is a general term, firmware exists for a lot of things on phone. The wireless chip for WiFi, GPS, and Bluetooth often has a firmware as can the GPU core among other things. These firmware files are usually located inside the SYSTEM or VENDOR partition. The modem firmware is special because it has its own separate Baseband Processor (BP) so the firmware is left out of the system image in its own partition.
Modem is not an Android-specific partition. It is tied to the hardware of the phone, but the kernel has a code allowing Android to interact with the hardware. But the baseband processor (BP) - which runs modem and is responsible for all communication through mobile networks e.g. call, SMS and internet - is totally isolated from Application Processor (the one we call CPU) and is not governed by Android kernel; it runs an independent RTOS.

RIL/Radio Interface Layer
This is not a separate partition, but a part of the ROM and is like a driver for the Radio. RIL daemons provides telephony and cellular data i.e. adds phone to smartphone. There is a matching RIL for each Baseband version and you can flash it to match your Baseband after flashing a ROM. Having mismatched RIL and Baseband can range from having no effect at all, slight battery drain, loss of roaming, or even no connection to the cell network. Many ROMs keep their RIL updated to the latest. Job of the RIL is to translate all the telephony requests from the Android telephony framework and map them to the corresponding AT commands to the modem, and back again. AT set of commands is used to communicate with modem i.e. baseband processor (BP) which is a must have processor on Android devices in addition to normal CPU i.e. Application Processor (AP).

TZ (TrustZone) - used by ARM processors as an additional lock to security features. It combines user's encryption key with a hardware specific key generated by encryption processor (like TPM on Windows) to make security breaching more difficult. It can also be used to implement Trusted Execution Environment (TEE).

RPM (Resource/Power Management) which starts executing Primary/Primitive BootLoader (PBL) in BootROM - controls power to radio, modem etc.
DSP (Digital Signal Processor) - by Qualcomm to assist in things like smooth video playback (realtime media and sensors processor) as well as runs RTOS for modem
HYP (Hypervisor) - Virtual Machine Monitor, to enable Virtual Machine platform

4. BOOTLOADERS
Bootloaders - in many steps - hand over charge to kernel after loading in RAM. These are mostly standalone ELF executable files becuase at this stage no filesystem is loaded and only executable code may work. These are all closed source components on Android device, provided by SoC vendors - either built-in or as binary blobs.
SBL - Secondary bootloader loaded by SoC, loads ABOOT in memory, also provides (Emergency) Download Mode (EDL) on many devices, a Firmware Update Protocol.
ABOOT (bootloader.img or aboot.mbn file in Factory Firmware) - Applications Bootloader is the main bootloader responsible for loading kernel or recovey and fastboot - a Firmware Update Protocol - as well.
Kernelflinger is a similar bootloader on Intel devices.

Read ANDROID BOOT PROCESS to know more about bootloaders.

5. CORE AOSP PARTITIONS
BOOT
- Kernel and initramfs (modern form of of ramdisk and ramfs/tmpfs)
A kernel is a layer of code that allows the OS and applications to interface with your phone's hardware. The degree to which you can access your phone's hardware features depends on the quality of code in the kernel. Several kernel code improvements give us additional features from our hardware that the stock kernel does not. When you flash a custom ROM, you automatically get a kernel. But you can also flash a standalone kernel on top of the existing one, effectively overwriting it. These days, the difference in custom kernels is less about new features and more about alternate configurations. Choosing a custom kernel is basically choosing one that works best with your ROM.
Device Tree Blob (DTB), along with hardware drivers, are baked with kernel source in boot.img. DTB is loaded by bootloader at boot time and passed to kernel so that it can discover hardware and create node points accordingly.
On a Linux system init along with scripts, binaries kernel drivers and modules (in initrd.img), kernel (vmlinuz executable) and bootloader configuration along with modules, they all reside on root or a separate partition (mounted) at /boot. While on Android, init along with a few binaries and configuration files and kernel reside in a separate partition named "boot" with a special filesystem. Boot.img is created using tools like mkbootimg after building kernel.

This is how kenrel and DTB are built:
vmlinux
> Image > zImage / Image.gz > Image.gz-dtb
  • vmlinux: Large sized non-bootable Linux kernel (executable) with debug symbols, just an intermediate step to producing vmlinuz
  • vmlinux.bin: Same as vmlinux binary but with removed symbols, produced by 'objcopy'
  • vmlinuz: Compressed and bootable Linux kernel file; one of zImage or bzImage formats; compressed using zlib, LZMA, gzip or bzip2 etc.
    • zImage: Smaller format, for old kernels
    • bzImage: Big zImage
  • Image: vmlinux.bin of embedded devices
  • Image.gz: zImage or bzImage of embedded devices
.dts (multiple) < > .dtb (1 or more)
Converted using dtc (device tree compiler)
  • .dtb is appended to zImage / Image.gz i.e. zImage-dtb / Image.gz-dtb (simply concatenate)
    • zImage-dtb > dtb Can be extracted using split-appended-dtb
  • Packed as a part of kernel, "--dt" option is not needed when creating boot.img
    • mkbootimg --kernel *.Image.gz-dtb --ramdisk *.cpio.gz --base . . . --offset . . . --tag-address . . . --cmdline . . .
  • .dtb is extracted as a part of kernel by unpackbootimg
.dtb < > dtb.img
Converted using mkdtimg
  • dtb.img is for dtb partition or second stage of boot.img
  • boot.img is created by using --dt option:
    • mkbootimg --dt dt.img --kernel *.Image.gz --ramdisk *.cpio.gz --base . . . --offset . . . --tag-address . . . --cmdline . . .
  • dtb.img is extracted separately by unpackbootimg
Further Reading: Device Tree Overlays and Android Boot and Recovery Images

SYSTEM - ROM / OS
Contains system applications and libraries that have AOSP source code. During normal operation, this partition is mounted read-only; its contents change only during an OTA update or when flashing a new OS. Most ROM's don't allow root level (Admin rights in Windows) access by default. So, "rooting" is required to modify the contents of this partition. This is the actual User Interface we use on our phone i.e. system apps are installed on this partition on /system/app directory. Another important directory is /system/bin which contains executable binaries to perform each and every action by OS in background (as daemons) or by user in shell (bash) scripts or CLI (command line interface). These are native binaries (developed in C / C++ mostly) as opposed to Android apps which are developed in Java. A minimal form of Linux commands is also included in AOSP as toolbox or toybox (or user can add busybox or individual static binaries). /system/lib directory contains native libraries (shared by applications commonly) with .so extensions just like .dll on Windows.

VENDOR
This partition is replaced with a shortcut (symbolic link in fact) to /system/vendor directory. It contains system applications and libraries that do not have source code available on AOSP but added by vendors (OEM's). During normal operation, this partition is mounted read-only; its contents change only during an OTA update. It also contains SoC firmware images i.e. hardware specific libraries and binaries (OpenGL, ISP...).
Proprietary blobs (HALs) usually live in (/system)/vendor as shared libraries (.so files) which are loaded by Android binders when processes call a hardware component. HAL (hardware abstraction layer) is userspace alternative to traditional Linux's system calls for drivers and is a kind of Google's standardization for OEMs/hardware vendors, though being abandoned by mainstream Linux.
PROJECT TREBLE
In an ideal world, there should be a generic AOSP OS and a single kernel for all Android devices, not tied to hardware and vendors. But unfortunately it isn't so because unlike PC world, there is no standardization in mobile world. AOSP is heavily modified on silicon vendor (SoC) as well as phone vendor level. One of the worst outcome of this situation is almost no Long Term Support (LTS). There are delayed or none updates once the consumers have phone, making it vulnerable to security issues and missing new features. Project Treble (starting from Android-8) addresses this issue somewhat by creating a separation between hardware specific code and generic AOSP code.
Previously, phone vendors used to get AOSP code from Google, mixing it with their own cutomizations (UI, apps etc.) and the hardware specific code from SoC vendor. If a minor fix needed to be applied to AOSP code, the whole process had to be repeated because code was intermingled and fixing one thing broke the other. Google resolved this issue by specifying /vendor partition for hardware specific code, /system containing only generic code. Interaction with AOSP code will be through HIDL interfaces, thus making it possible to upgrade the both codes independently. /oem and /odm partitions were added previously for the same purpose.

USERDATA
User applications are installed in different folders under /data. Apps data (user and system) is stored in /data/data. User personal data and some apps data is stored in /data/media. /data/media is also emulated as internal SDCard at /storage/emulated and symlinked at /sdcard. Personalized and apps settings are also stored in this partition. A folder /data/dalvik contains, in simple words, extracted apps to boost loading process. Java bytecode of Android apps is converted to executable code (.odex) by Dalvik Virtual Machine, separate instance of which is launched by zygote (an Android init daemon) for every app.
This partition is not normally touched by the OTA update process. A Factory Reset wipes this partition, normally excluding /data/media i.e. personal data.
When you do a factory reset (AKA: wipe, hard reset, factory wipe, etc.), you are erasing the /data and /cache partitions. Note that a factory reset does NOT put your phone back to its factory state from an OS standpoint. OS upgrades will stay because the OS lives in /system, and that is not touched during a factory reset. So it's not a factory reset. It's a factory DATA reset actually.

RECOVERY
Holds alternate boot partition and the recovery program that lets the device boot into a recovery console for performing advanced recovery and maintenance operations. It contains a second complete Linux system i.e. independent OS, including a user-interface application, kernel and the special recovery binary that reads a package and uses its contents to update i.e. flash or wipe itself or any other partition particularly during OTA updates.
Recovery is also the most commonly used method to flash custom ROM's.
ADB sideload mode through PC is a replacement of flashing files (usually .zip) through Recovery. ADB works when phone is switched on in Recovery (or ROM). ADB/fastboot setup is to be made on PC to use this mode.

CACHE - cached (frequently accessed) data from OS usage and contains the firmware update package downloaded from server during OTA updates. Temporary holding area used by a few applications with the expectation that files can disappear at any time. Major use is by recovery and OTA updates. Recovery last_log is also written to this partition.

6. OTHER PARTITIONS
CUST
- also CUSTOM or PRELOAD on some devices, it's used by stock ROM's, holding some preloaded system apps and regional settings which are installed on first use.

MISC - also FOTA on older devices
It's a tiny partition used by recovery to communicate with bootloader store away some information about what it's doing in case the device is restarted while the OTA package is being applied.
It is a boot mode selector used to pass data among various stages of the boot chain (boot into recovery mode, fastboot etc.). e.g. if it is empty (all zero), system boots normally. If it contains recovery mode selector, system boots into recovery mode.
It may also carry some necessarily required information in the form of switches to control hardware or settings related tasks such as CID (Carrier or Region ID) information and USB configurations etc.

PERSIST - contains data which shouldn't be changed after the device is shipped, e.g. DRM related files, sensor reg file (sns.reg) and calibration data of chips; wifi, bluetooth, camera etc.
Some package installers such as OpenGapps also make use of this partition to read configuration file.

EFS, MODEMST1, MODEMST2, FSG, BACKUP
These all are related to IMEI; a unique number used by GSM networks to identify and trace a mobile phone.
EFS may contain hardware info like configuration files, WiFi/BlueTooth MAC’s, IMEI (or ESN for a CDMA based device) etc.
EFS and MODEMST1 may be a single partition on some phones.
FSG (FileSystem Golden copy) and BACKUP are backups of MODEMST1 and MODEMST2 respectively. If MODEMST1 or MODEMST2 are erased (by wrong factory flashing say) and phone notices an invalid partition, FSG and BACKUP will be restored.
MODEMST1 and MODEMST2 also contains modem firmware files.
PARAM - stores a number of parameters, variables and settings of the hardware. It contains info whether MODEMST partitions are backed up or not. Also debug settings, custom ROMs flash count, current stage boot process etc.

OEM - like VENDOR, it incorporates OEM (Original Equipment Manufacturer i.e. hardware manufacturer or Mobile Phone brand) small customization (modifications) to original Android (AOSP) during OTA updates such as customized system properties values etc.
PAD - related to OEM
OTA, FOTA - OTA updates
DDR - Double Data Rate RAM
FSC - Modem FileSystem Cookies
SSD - Secure Software Download, a memory based file system for secure storage, stores some encrypted RSA keys
DEVINFO - device information including: is_unlocked (aboot), is_tampered, is_verified, charger_screen_enabled, display_panel, bootloader_version, radio_version etc. Contents of this partition are displayed by "fastboot oem device-info" command in human readable format. Before loading boot.img or recovery.img, bootloader verifies the locked state from this partition.
CONFIG/FRP/PDB - saves state of Factory Reset Protection (FRP), "Allow bootloader (OEM) unlocking" . (Developer Options), asks already associated account info. This partition is erased/reset if Factory Reset done from Settings.
DEVCFG - used by TZ for upgrades
LKSECAPP - "LK (Little Kernel) Security App", related to RPM, TZ online verification / update
LIMITS - Qualcomm Limits Management Hardware (LMh) driver in SBL writes the data in this partition to use for later reboots
SYSCFG - Qualcomm CPR (Core Power Reduction) Regulator for better performance and power saving of application processor by voltage control
DIP, MDTP - boot verification, use Qualcomm SafeSwitch technology to lock and track theft phones
CMNLIB, KEYMASTER - verified boot
SEC - contains fuse settings, mainly for secure boot (signing bootloaders for chain of trust) and oem setting
KEYSTORE - related to /data Full Disc Encryption (FDE)
MCFG - (Modem Configuration Framework) - on dual SIM devices, loads MBN (modem binary) files depending on SIM/carrier
SPLASH - splash image or boot logo which appears when device boots (at ABOOT stage).
CHGLOGO - charging screen that appears when charger is connected to powered off device.
MSADP, APDP, DPO - related to debug policies
GROW - empty for future expansion

7. FILESYSTEMS
Supported filesystems by your kernel can be viwewd by:
Code:
~# cat /proc/filesystems

Partitions with Mountable Filesystems
Following partitions are mounted during boot process:
system, vendor, odm, userdata (mounted at /data), cache, cust, persist (mounted at /persist or /mnt/vendor/persist), modem (mounted at /firmware or /vendor/firmware_mnt), dsp (mounted at /dsp or /vendor/dsp)
Modem is formatted as vfat while all others are usually ext4 or f2fs on newer devices.
All of these are listed in /fstab.* file which is processes by init. Starting with Android 8.0 (Treble release), fstab.* is moved to /vendor/etc/ and system, vendor and odm entries are included in dtb.

Other partitions don't contain a mountable filesystem. However, we may try to get an idea of the contents by reading smaller partitions e.g.:
Code:
~# cat /dev/block/bootdevice/by-name/config | strings
~# cat /dev/block/bootdevice/by-name/misc | strings

Pseudo / Virtual / in-Memory Filesystems (Kernel space)
These filesystems don't rely on a physical persistent storage but just live in RAM, to provide kernel services interfaces in user space.
rootfs (/) - mounted by kernel before calling init. More details here
sysfs (/sys) - information related to devices, populated by kernel
devpts (/dev/pts) - character device files representing slave side of pseudo terminal pairs
proc (/proc) - information related to all processes, updated as processes are started / killed
tmpfs (/dev) - all device nodes updated from sysfs, accessible from user space
configfs (/config) - intergrated with userspace sdcardfs, controls apps permissions to directories on internal/external sdcard by VOLume Daeomon, a replacement of fusefs
pstore (/sys/fs/pstore) - persistent storage, a replacement of /proc/last_kmsg, saves last kernel console messages on panic / crashes / sudden reboots, solution to volatile nature of pseudo filesystems
cgroup - cgroups manage hardware resources allocation to processes as per load
selinuxfs (/sys/fs/selinux) - implementation of Security-Enahanced Linux, a mandatory access controls (MAC) to manage file permissions, better than traditional Discretionary Access Control (DAC) mechanism (Read-Write-eXecute) of Linux
debugfs (/sys/kernel/debug) - to monitor and debug kernel space implementations from user space
tracefs (/sys/kernel/debug/tracing) - debugfs with better security
functionfs (/dev/usb-ffs/adb) - integrated with configfs, manages USB gadgets, ADB is implemented through functionfs on Android

FILESYSTEM TREE MOUNTED BY INIT: ANDROID vs. LINUX

8. Factory Firmware and Flashable ROMs:

When you flash a custom ROM, that ROM typically includes a kernel and an OS. That means the /boot and /system partitions will be modified at a minimum. Some ROMs require a clean install, so a format of the /data and /cache partitions is sometimes built into the .zip that you flash. This is essentially doing a Factory Reset.
Read here to know more about flashing partitions.
Factory Firmware contains original iamge files of almsot all important partitions. It's provided by OEM's, usually as a package which also incude a flasher software for PC. Or a general flasher software may be uses such as QFIL.

ROM Development
A ROM developer downloads AOSP source code from Google while device tree, driver binaries and kernel source code is provided by (ODM's through) OEM's, if they are generous enough. OEM's manufacture and sell devices themselves while ODM's sell to white-labelers who brand them under their own names. Original Android kernel tree is provided by Google which in turn is taken from Linux and then modified by Google for Android-specific needs.

RELATED:
 
Last edited:

saprey

Member
Jul 16, 2017
17
0
Drivers Partition

What are partitions responsible on drivers like sound and camera,
I restored ROM using TWRP but now, Sound and Camera don't work,
any help?
 

TommyWhite

Senior Member
Oct 5, 2017
72
3
40
Leeuwarden
Oh, I misunderstood.
It was about public storages (so whats accessible without root, right??).

It said
Public storage (primaire): /storage/emulated/0
Public storage (secondaire): /storage/94F1-34D8 (I didnt realise that was my sd card ...)
RootFs: /
System: /system

Like a said 'a real newbie' ;)
 

mirfatif

Senior Member
Oct 18, 2016
659
419
t.me
Oh, I misunderstood.
It was about public storages (so whats accessible without root, right??).

It said
Public storage (primaire): /storage/emulated/0
Public storage (secondaire): /storage/94F1-34D8 (I didnt realise that was my sd card ...)
RootFs: /
System: /system

Like a said 'a real newbie' ;)
Something like this attachment?
 

Attachments

  • IMG_20171108_035450.jpg
    IMG_20171108_035450.jpg
    98.2 KB · Views: 2,114

argon9898

Member
Feb 8, 2013
47
4
While on some devices there is no bootloader partition at all and bootloader(s) resides on SoC.
Great post btw! With the bootloader section mentioning like the above, I have a question: I'm having a device with Snapdragon 810 SoC and wasn't able to find the bootloader partition (or at least I didn't know it has because I couldn't get it to boot into that mode). So does that mean the bootloader is on the SoC? How do I figure it out if it exists on the chip?
 

mirfatif

Senior Member
Oct 18, 2016
659
419
t.me
Great post btw! With the bootloader section mentioning like the above, I have a question: I'm having a device with Snapdragon 810 SoC and wasn't able to find the bootloader partition (or at least I didn't know it has because I couldn't get it to boot into that mode). So does that mean the bootloader is on the SoC? How do I figure it out if it exists on the chip?
Booting in bootloader (or it's equivalent; like fastboot) mode is dependent on the phone manufacturer. Though most of the hardware manufacturers allow users to access bootloader for repair/maintenance or modified boot chain, some may restrict this for Digital Rights Management or to gain forced customer loyalty :D , irrespective of where bootloader resides. On most phones it's a partition. You may check your partition table to know about all partitions.
 

mirfatif

Senior Member
Oct 18, 2016
659
419
t.me
Hi @mirfatif , what a post! Hats off to you. By the way, where does the blobs/ HALs go when we flash a new ROM zip?

Thanks for mentioning. I have added this to my post. By "blolbs" you mean DTB or hardware drivers? Well AFAIK, the blobs are included in every ROM where "ROM" is boot.img and system.img at least.
A ROM developer downloads AOSP source code from Google while device tree (map of hardware components), driver binaries and kernel source code is provided by (ODM's through) OEM's, if they are generous enough. OEM's manufacture and sell devices themselves while ODM's sell to white-labelers who brand them under their own names. Original Android kernel tree is provided by Google which in turn is taken from Linux and then modified by Google for Android-specific needs. DTB and drivers are baked with kernel source in boot.img though DTB may live on a separate dtb partition as specified by AOSP (and was the proposed solution for ARM based embedded Linux devices before Android's birth) but I don't think that is widely practiced. DTB is loaded by bootloader at boot time and passed to kernel so that it can discover hardware and create node points accordingly. Proprietary blobs (HALs) usually live in (/system)/vendor as shared libraries (.so files) which are loaded by Android binders when processes call a hardware component. HAL is userspace alternative to traditional Linux's system calls for drivers and is a kind of Google's standardization for OEMs/hardware vendors.
 

pindonga123

Senior Member
May 28, 2015
51
1
Hello everyone. I tell you that one day flashing my oneplus 5 lost the wifi. The MAC address shows me the typical 02: 00: 00: 00: 00: 00 address. The way to fix it is updating the Oreo but I could never do it, it is always in bootloop, I read all the forums and there is no case, do what I always do the same. It happens in many oneplus 5. So I forgot to fix it in that way. The other thing I saw is hundreds of forums with that problem but I could not fix it either, I've been doing it for three months now. What I am trying now is to erase all the partitions except recovery or bootloader but the phone does not start anymore. What I want is to delete all the partitions associated with wifi, delete modem1, modem2, persist, fsg but nothing, I just managed to lose the imei that does not matter to me because I have back up of the efs folder and even the qcn file of the phone. I know it's a lot of work but if someone tells me that they control each partition, I could erase it, load everything from scratch and that's it. Would someone give me a hand so I can fix that damn wifi on the phone ?. Thank you.
--------------------------------------------------------------------------------------------------------------------------------------
drwxr-xr-x 2 root root 1440 1970-05-03 14:23 .
drwxr-xr-x 4 root root 1600 1970-05-03 14:23 ..
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 LOGO -> /dev/block/sde18
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 abl -> /dev/block/sde16
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 ablbak -> /dev/block/sde17
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 apdp -> /dev/block/sde31
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 bluetooth -> /dev/block/sde24
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 boot -> /dev/block/sde19
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 boot_aging -> /dev/block/sde20
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 cache -> /dev/block/sda3
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 cdt -> /dev/block/sdd2
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 cmnlib -> /dev/block/sde27
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 cmnlib64 -> /dev/block/sde29
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 cmnlib64bak -> /dev/block/sde30
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 cmnlibbak -> /dev/block/sde28
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 config -> /dev/block/sda12
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 ddr -> /dev/block/sdd3
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 devcfg -> /dev/block/sde39
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 devinfo -> /dev/block/sde23
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 dip -> /dev/block/sde14
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 dpo -> /dev/block/sde33
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 dsp -> /dev/block/sde11
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 frp -> /dev/block/sda6
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 fsc -> /dev/block/sdf4
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 fsg -> /dev/block/sdf3
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 fw_4g9n4 -> /dev/block/sde45
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 fw_4j1ed -> /dev/block/sde43
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 fw_4t0n8 -> /dev/block/sde46
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 fw_8v1ee -> /dev/block/sde44
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 hyp -> /dev/block/sde5
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 hypbak -> /dev/block/sde6
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 keymaster -> /dev/block/sde25
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 keymasterbak -> /dev/block/sde26
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 keystore -> /dev/block/sda5
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 limits -> /dev/block/sde35
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 logdump -> /dev/block/sde40
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 logfs -> /dev/block/sde37
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 md5 -> /dev/block/sdf5
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 mdtp -> /dev/block/sde15
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 mdtpsecapp -> /dev/block/sde12
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 mdtpsecappbak -> /dev/block/sde13
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 minidump -> /dev/block/sde47
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 misc -> /dev/block/sda4
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 modem -> /dev/block/sde10
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 modemst1 -> /dev/block/sdf1
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 modemst2 -> /dev/block/sdf2
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 msadp -> /dev/block/sde32
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 oem_dycnvbk -> /dev/block/sda7
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 oem_stanvbk -> /dev/block/sda8
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 param -> /dev/block/sda9
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 persist -> /dev/block/sda2
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 pmic -> /dev/block/sde8
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 pmicbak -> /dev/block/sde9
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 recovery -> /dev/block/sde22
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 reserve -> /dev/block/sdd1
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 reserve1 -> /dev/block/sda10
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 reserve2 -> /dev/block/sda11
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 rpm -> /dev/block/sde1
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 rpmbak -> /dev/block/sde2
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 sec -> /dev/block/sde7
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 splash -> /dev/block/sde34
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 ssd -> /dev/block/sda1
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 sti -> /dev/block/sde38
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 storsec -> /dev/block/sde41
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 storsecbak -> /dev/block/sde42
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 system -> /dev/block/sde21
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 toolsfv -> /dev/block/sde36
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 tz -> /dev/block/sde3
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 tzbak -> /dev/block/sde4
lrwxrwxrwx 1 root root 16 1970-05-03 14:23 userdata -> /dev/block/sda13
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 xbl -> /dev/block/sdb1
lrwxrwxrwx 1 root root 15 1970-05-03 14:23 xblbak -> /dev/block/sdc1
 
thank you

This is one of the best posts that I've ever read. I'm a hobbyist and reverse engineer learn. My primary phones are Samsung S 6 7 and 8 and I've soft bricked phones them more times than I can count (but recovered) justifying it as a learning experience. Sort of like putting your hand in the fire several times and calling it a learning experience. your post opens up more questions which are great. I root all my phones and I have a fear of new security patches disguised as updates disabling what methods work last week so to speak


So if I understand finally there is a section in bootloaders which is the first bootloader that is static yet upgradable but not downgradable as you referred to like the BIOS on PCs which acts as a verification process so you can't flash downgradable security patches. Much like I've encountered with partcyborg great work on rooting the S8 snapdragon however once you upgraded to the bootloader 2 you couldn't go back to the bootloader one. This is in reference to the build, not the partition.

If someone does reply, I'd like to know can you mod a certain file and Odin in the bootloader section when flashing an update to ensure that you stay at a certain bootloader level while the other files such as AP CP and CSC remain intact from the sam mobile stock firmware.(which I assume the term combo firmware file originates)
My most recent encounters are the device and binary are not the same which I attribute to this problem.


In theory from what I understand the phone has a section that is not Factory resettable which is the NAND that contains read-only but system upgrade information? However, it can be modified by a power Superuser rooted? This obviously risking hard bricking a phone

When upgrading firmware specifically the bootloader file in Odin what file(s) {bin} are essential to the new modification patches and can those files be substituted?

Any comment is considered very helpful. Odin itself is coming out with different versions for structures (prince cosmey) for example.

I explore the system file structure often wondering what I could change or alter as simple as a 0 or 1 or a true or a false to enable or disable my ability to access what I feel I need to access.

I could buy the z3x Samprotools but it defeats my intentions to learn the details.

If you do have a suggestion on a GUI Windows-based tool it would be great. Don't know Linux just as a footnote

Once again what a great post and definition of the different sections of terminology it's just enough to educate me and confuse me at the same time keep doing what you're doing. Any tricks or tips will be very appreciated.
 
  • Like
Reactions: beeshyams

chankruze

Senior Member
Jun 30, 2017
225
256
Balasore
chankruze.github.io
Curious Q.!

what about these two ?
Code:
rpm -> /dev/block/mmcblk0p2
rpmbak -> /dev/block/mmcblk0p11
my phone is MOTO-G5-PLUS (potter)
whole partition table is here:
Code:
←7←[r←[999;999H←[6n←8potter:/ # ls -l /dev/block/bootdevice/by-name
total 0
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 DDR -> /dev/block/mmcblk0p23
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 aboot -> /dev/block/mmcblk0p5
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 abootbak -> /dev/block/mmcblk0p14
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 apdp -> /dev/block/mmcblk0p45
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 boot -> /dev/block/mmcblk0p37
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 cache -> /dev/block/mmcblk0p52
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 carrier -> /dev/block/mmcblk0p34
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 cid -> /dev/block/mmcblk0p32
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 cmnlib -> /dev/block/mmcblk0p6
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 cmnlib64 -> /dev/block/mmcblk0p7
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 cmnlib64bak -> /dev/block/mmcblk0p16
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 cmnlibbak -> /dev/block/mmcblk0p15
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 devcfg -> /dev/block/mmcblk0p4
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 devcfgbak -> /dev/block/mmcblk0p13
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 dip -> /dev/block/mmcblk0p42
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 dpo -> /dev/block/mmcblk0p47
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 dsp -> /dev/block/mmcblk0p22
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 frp -> /dev/block/mmcblk0p31
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 fsc -> /dev/block/mmcblk0p20
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 fsg -> /dev/block/mmcblk0p29
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 hw -> /dev/block/mmcblk0p50
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 keymaster -> /dev/block/mmcblk0p8
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 keymasterbak -> /dev/block/mmcblk0p17

lrwxrwxrwx 1 root root 21 1970-08-28 23:29 kpan -> /dev/block/mmcblk0p36
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 limits -> /dev/block/mmcblk0p40
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 logo -> /dev/block/mmcblk0p33
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 logs -> /dev/block/mmcblk0p44
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 metadata -> /dev/block/mmcblk0p35
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 misc -> /dev/block/mmcblk0p39
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 modem -> /dev/block/mmcblk0p19
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 modemst1 -> /dev/block/mmcblk0p27
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 modemst2 -> /dev/block/mmcblk0p28
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 mota -> /dev/block/mmcblk0p41
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 msadp -> /dev/block/mmcblk0p46
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 oem -> /dev/block/mmcblk0p51
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 padA -> /dev/block/mmcblk0p48
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 persist -> /dev/block/mmcblk0p30
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 prov -> /dev/block/mmcblk0p9
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 provbak -> /dev/block/mmcblk0p18
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 recovery -> /dev/block/mmcblk0p38
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 rpm -> /dev/block/mmcblk0p2
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 rpmbak -> /dev/block/mmcblk0p11
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 sbl1 -> /dev/block/mmcblk0p1
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 sbl1bak -> /dev/block/mmcblk0p10
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 sec -> /dev/block/mmcblk0p24
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 sp -> /dev/block/mmcblk0p49
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 ssd -> /dev/block/mmcblk0p21
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 syscfg -> /dev/block/mmcblk0p43
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 system -> /dev/block/mmcblk0p53
lrwxrwxrwx 1 root root 20 1970-08-28 23:29 tz -> /dev/block/mmcblk0p3
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 tzbak -> /dev/block/mmcblk0p12
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 userdata -> /dev/block/mmcblk0p54
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 utags -> /dev/block/mmcblk0p25
lrwxrwxrwx 1 root root 21 1970-08-28 23:29 utagsBackup -> /dev/block/mmcblk0p26
potter:/ #
 
Last edited:
  • Like
Reactions: adeii

chankruze

Senior Member
Jun 30, 2017
225
256
Balasore
chankruze.github.io
what about these two ?

RPM (Resource/Power Management) or Primary BootLoader (PBL); controls power to radio, modem etc.

I got a script from a xda thread in which OP mentioned that this script is for wiping dalvik/ART cache.
Before flashing it i decided to analyse it,what i found that it was erasing my RPM partition on mmcblk0p2.

Is it really for dalvik cache ?
 

Top Liked Posts

  • There are no posts matching your filters.
  • 99
    NOTE:
    I'm not a developer or something even near to that. I'm a newbie and will be, seems so. All information provided here is copied and compiled from different internet sources like this and many others.
    This information is according to best of my knowledge and comprehension and is just for curious souls like me who want to understand things in quite simple words. It might be wrong and I will open-heartedly welcome any correction or addition from anyone.
    I'm not responsible for any harm to you or your device resulting from this.


    1. PARTITION TABLE

    The Phone's Internal Memory (eMMC or UFS; not the SD card) is solid-state (flash) memory, aka NAND. Raw NAND, as it's called, is basically a pure flash memory dependent on CPU to control it. But in order to use flash memory just like a traditional hard drive (block device), NAND is equipped with an (embedded multimedia) micro-controller. It's called eMMC.

    eMMC can be partitioned much like a hard drive on PC. PC's have traditionally been partitioned with BIOS compatible Master Boot Record (MBR) scheme in which first sector of disk contains the details of partitions called Partition Table. Limited size of boot sector (512 bytes) puts a limitation of at maximum 4 (primary) partitions listed in MBR. Extended partition has been used for 4+ partitions.

    GUID Partition Table (GPT) was introduced with UEFI booting system which isn't dependent on first boot sector and hence may contain up to 128 partitions. GPT also does CRC check, has backup GPT, identifies partitions by GUID and partitions have a label.

    Android devices use GPT. We can view and manipulate GPT using Linux tools such as parted and gdisk while fdisk is the traditional tool for MBR partitions.
    To view partition table on internal memory:
    Code:
    ~# parted /dev/block/mmcblk0
    (parted) p free
    
    ~# gdisk -l /dev/block/mmcblk0

    (The external SD Card can also be partitioned to include a section dedicated to storing user apps (like Link2SD does) or to create partitions for secondary or tertiary OS on Android device using some multiboot kernel and recovery system). Even we can put whole OS/ROM on an SD card.

    2. BRIEF INTRO
    Contents of Android partitions can be partially or completely modified by flashing an image (filesystem .img or executable binary or a flashable zip) to them. But we never need to modify most of them and whatever manufacturer wrote on them, resides there unmodified (read-only) for the whole of device life. A user uses only one partition /data to save personal data like photos, music etc. All the other are for device to run. There are typically in the range of 50 partitions on an Android device but only a few partitions are modified for the purpose of adding new features or upgrading the device. A custom ROM or minor upgrade is also limited to modify /boot, /system and /data partitions usually. Most of the partitions are almost intact, containing bootloaders, firmwares, settings etc. Here is a "summarized" detail to these partitions which matter to a common but interested user.
    On most devices /system and /data are larger partitions (on some devices /custom or a similar partition too) covering almost 90% of eMMC. All others are smaller ones of a few KB's or MB's.

    3. SoC / CHIPSET / PROCESSORS RELATED PARTITIONS
    SoC is the first component when we start a PC or Mobile phone which initialzes hardware and processors and loads bootloaders in memory to bootstrap OS. It's an integrated chip containing multiple things e.g. CPU, GPU, modem, wifi etc. It varies for device manufacturers and SoC vendors (chipset plus processor).
    Some partitions are specific to SoC, most of them are closed-source executable binary blobs (like aboot, sbl, rpm, tz, cmnlib, devcfg, keymaster, lksecapp and others on a Qualcomm device), loaded step-by-step by bootloaders.

    MODEM or RADIO - the phone's radio
    Also called baseband, it is responsible for signals and on older devices may control wifi, bluetooth, and GPS (on most newer devices, these are handled by the kernel and ROM). Upgrades are country dependent and may improve or diminish battery performance, network signal strength, and roaming capability. It is also sometimes required to have a minimum Baseband version to use a ROM so that the RIL will play nice with the Baseband.
    Modem firmware is a mini-OS for the cellular radio chip which has its own processor. Firmware is a general term, firmware exists for a lot of things on phone. The wireless chip for WiFi, GPS, and Bluetooth often has a firmware as can the GPU core among other things. These firmware files are usually located inside the SYSTEM or VENDOR partition. The modem firmware is special because it has its own separate Baseband Processor (BP) so the firmware is left out of the system image in its own partition.
    Modem is not an Android-specific partition. It is tied to the hardware of the phone, but the kernel has a code allowing Android to interact with the hardware. But the baseband processor (BP) - which runs modem and is responsible for all communication through mobile networks e.g. call, SMS and internet - is totally isolated from Application Processor (the one we call CPU) and is not governed by Android kernel; it runs an independent RTOS.

    RIL/Radio Interface Layer
    This is not a separate partition, but a part of the ROM and is like a driver for the Radio. RIL daemons provides telephony and cellular data i.e. adds phone to smartphone. There is a matching RIL for each Baseband version and you can flash it to match your Baseband after flashing a ROM. Having mismatched RIL and Baseband can range from having no effect at all, slight battery drain, loss of roaming, or even no connection to the cell network. Many ROMs keep their RIL updated to the latest. Job of the RIL is to translate all the telephony requests from the Android telephony framework and map them to the corresponding AT commands to the modem, and back again. AT set of commands is used to communicate with modem i.e. baseband processor (BP) which is a must have processor on Android devices in addition to normal CPU i.e. Application Processor (AP).

    TZ (TrustZone) - used by ARM processors as an additional lock to security features. It combines user's encryption key with a hardware specific key generated by encryption processor (like TPM on Windows) to make security breaching more difficult. It can also be used to implement Trusted Execution Environment (TEE).

    RPM (Resource/Power Management) which starts executing Primary/Primitive BootLoader (PBL) in BootROM - controls power to radio, modem etc.
    DSP (Digital Signal Processor) - by Qualcomm to assist in things like smooth video playback (realtime media and sensors processor) as well as runs RTOS for modem
    HYP (Hypervisor) - Virtual Machine Monitor, to enable Virtual Machine platform

    4. BOOTLOADERS
    Bootloaders - in many steps - hand over charge to kernel after loading in RAM. These are mostly standalone ELF executable files becuase at this stage no filesystem is loaded and only executable code may work. These are all closed source components on Android device, provided by SoC vendors - either built-in or as binary blobs.
    SBL - Secondary bootloader loaded by SoC, loads ABOOT in memory, also provides (Emergency) Download Mode (EDL) on many devices, a Firmware Update Protocol.
    ABOOT (bootloader.img or aboot.mbn file in Factory Firmware) - Applications Bootloader is the main bootloader responsible for loading kernel or recovey and fastboot - a Firmware Update Protocol - as well.
    Kernelflinger is a similar bootloader on Intel devices.

    Read ANDROID BOOT PROCESS to know more about bootloaders.

    5. CORE AOSP PARTITIONS
    BOOT
    - Kernel and initramfs (modern form of of ramdisk and ramfs/tmpfs)
    A kernel is a layer of code that allows the OS and applications to interface with your phone's hardware. The degree to which you can access your phone's hardware features depends on the quality of code in the kernel. Several kernel code improvements give us additional features from our hardware that the stock kernel does not. When you flash a custom ROM, you automatically get a kernel. But you can also flash a standalone kernel on top of the existing one, effectively overwriting it. These days, the difference in custom kernels is less about new features and more about alternate configurations. Choosing a custom kernel is basically choosing one that works best with your ROM.
    Device Tree Blob (DTB), along with hardware drivers, are baked with kernel source in boot.img. DTB is loaded by bootloader at boot time and passed to kernel so that it can discover hardware and create node points accordingly.
    On a Linux system init along with scripts, binaries kernel drivers and modules (in initrd.img), kernel (vmlinuz executable) and bootloader configuration along with modules, they all reside on root or a separate partition (mounted) at /boot. While on Android, init along with a few binaries and configuration files and kernel reside in a separate partition named "boot" with a special filesystem. Boot.img is created using tools like mkbootimg after building kernel.

    This is how kenrel and DTB are built:
    vmlinux
    > Image > zImage / Image.gz > Image.gz-dtb
    • vmlinux: Large sized non-bootable Linux kernel (executable) with debug symbols, just an intermediate step to producing vmlinuz
    • vmlinux.bin: Same as vmlinux binary but with removed symbols, produced by 'objcopy'
    • vmlinuz: Compressed and bootable Linux kernel file; one of zImage or bzImage formats; compressed using zlib, LZMA, gzip or bzip2 etc.
      • zImage: Smaller format, for old kernels
      • bzImage: Big zImage
    • Image: vmlinux.bin of embedded devices
    • Image.gz: zImage or bzImage of embedded devices
    .dts (multiple) < > .dtb (1 or more)
    Converted using dtc (device tree compiler)
    • .dtb is appended to zImage / Image.gz i.e. zImage-dtb / Image.gz-dtb (simply concatenate)
      • zImage-dtb > dtb Can be extracted using split-appended-dtb
    • Packed as a part of kernel, "--dt" option is not needed when creating boot.img
      • mkbootimg --kernel *.Image.gz-dtb --ramdisk *.cpio.gz --base . . . --offset . . . --tag-address . . . --cmdline . . .
    • .dtb is extracted as a part of kernel by unpackbootimg
    .dtb < > dtb.img
    Converted using mkdtimg
    • dtb.img is for dtb partition or second stage of boot.img
    • boot.img is created by using --dt option:
      • mkbootimg --dt dt.img --kernel *.Image.gz --ramdisk *.cpio.gz --base . . . --offset . . . --tag-address . . . --cmdline . . .
    • dtb.img is extracted separately by unpackbootimg
    Further Reading: Device Tree Overlays and Android Boot and Recovery Images

    SYSTEM - ROM / OS
    Contains system applications and libraries that have AOSP source code. During normal operation, this partition is mounted read-only; its contents change only during an OTA update or when flashing a new OS. Most ROM's don't allow root level (Admin rights in Windows) access by default. So, "rooting" is required to modify the contents of this partition. This is the actual User Interface we use on our phone i.e. system apps are installed on this partition on /system/app directory. Another important directory is /system/bin which contains executable binaries to perform each and every action by OS in background (as daemons) or by user in shell (bash) scripts or CLI (command line interface). These are native binaries (developed in C / C++ mostly) as opposed to Android apps which are developed in Java. A minimal form of Linux commands is also included in AOSP as toolbox or toybox (or user can add busybox or individual static binaries). /system/lib directory contains native libraries (shared by applications commonly) with .so extensions just like .dll on Windows.

    VENDOR
    This partition is replaced with a shortcut (symbolic link in fact) to /system/vendor directory. It contains system applications and libraries that do not have source code available on AOSP but added by vendors (OEM's). During normal operation, this partition is mounted read-only; its contents change only during an OTA update. It also contains SoC firmware images i.e. hardware specific libraries and binaries (OpenGL, ISP...).
    Proprietary blobs (HALs) usually live in (/system)/vendor as shared libraries (.so files) which are loaded by Android binders when processes call a hardware component. HAL (hardware abstraction layer) is userspace alternative to traditional Linux's system calls for drivers and is a kind of Google's standardization for OEMs/hardware vendors, though being abandoned by mainstream Linux.
    PROJECT TREBLE
    In an ideal world, there should be a generic AOSP OS and a single kernel for all Android devices, not tied to hardware and vendors. But unfortunately it isn't so because unlike PC world, there is no standardization in mobile world. AOSP is heavily modified on silicon vendor (SoC) as well as phone vendor level. One of the worst outcome of this situation is almost no Long Term Support (LTS). There are delayed or none updates once the consumers have phone, making it vulnerable to security issues and missing new features. Project Treble (starting from Android-8) addresses this issue somewhat by creating a separation between hardware specific code and generic AOSP code.
    Previously, phone vendors used to get AOSP code from Google, mixing it with their own cutomizations (UI, apps etc.) and the hardware specific code from SoC vendor. If a minor fix needed to be applied to AOSP code, the whole process had to be repeated because code was intermingled and fixing one thing broke the other. Google resolved this issue by specifying /vendor partition for hardware specific code, /system containing only generic code. Interaction with AOSP code will be through HIDL interfaces, thus making it possible to upgrade the both codes independently. /oem and /odm partitions were added previously for the same purpose.

    USERDATA
    User applications are installed in different folders under /data. Apps data (user and system) is stored in /data/data. User personal data and some apps data is stored in /data/media. /data/media is also emulated as internal SDCard at /storage/emulated and symlinked at /sdcard. Personalized and apps settings are also stored in this partition. A folder /data/dalvik contains, in simple words, extracted apps to boost loading process. Java bytecode of Android apps is converted to executable code (.odex) by Dalvik Virtual Machine, separate instance of which is launched by zygote (an Android init daemon) for every app.
    This partition is not normally touched by the OTA update process. A Factory Reset wipes this partition, normally excluding /data/media i.e. personal data.
    When you do a factory reset (AKA: wipe, hard reset, factory wipe, etc.), you are erasing the /data and /cache partitions. Note that a factory reset does NOT put your phone back to its factory state from an OS standpoint. OS upgrades will stay because the OS lives in /system, and that is not touched during a factory reset. So it's not a factory reset. It's a factory DATA reset actually.

    RECOVERY
    Holds alternate boot partition and the recovery program that lets the device boot into a recovery console for performing advanced recovery and maintenance operations. It contains a second complete Linux system i.e. independent OS, including a user-interface application, kernel and the special recovery binary that reads a package and uses its contents to update i.e. flash or wipe itself or any other partition particularly during OTA updates.
    Recovery is also the most commonly used method to flash custom ROM's.
    ADB sideload mode through PC is a replacement of flashing files (usually .zip) through Recovery. ADB works when phone is switched on in Recovery (or ROM). ADB/fastboot setup is to be made on PC to use this mode.

    CACHE - cached (frequently accessed) data from OS usage and contains the firmware update package downloaded from server during OTA updates. Temporary holding area used by a few applications with the expectation that files can disappear at any time. Major use is by recovery and OTA updates. Recovery last_log is also written to this partition.

    6. OTHER PARTITIONS
    CUST
    - also CUSTOM or PRELOAD on some devices, it's used by stock ROM's, holding some preloaded system apps and regional settings which are installed on first use.

    MISC - also FOTA on older devices
    It's a tiny partition used by recovery to communicate with bootloader store away some information about what it's doing in case the device is restarted while the OTA package is being applied.
    It is a boot mode selector used to pass data among various stages of the boot chain (boot into recovery mode, fastboot etc.). e.g. if it is empty (all zero), system boots normally. If it contains recovery mode selector, system boots into recovery mode.
    It may also carry some necessarily required information in the form of switches to control hardware or settings related tasks such as CID (Carrier or Region ID) information and USB configurations etc.

    PERSIST - contains data which shouldn't be changed after the device is shipped, e.g. DRM related files, sensor reg file (sns.reg) and calibration data of chips; wifi, bluetooth, camera etc.
    Some package installers such as OpenGapps also make use of this partition to read configuration file.

    EFS, MODEMST1, MODEMST2, FSG, BACKUP
    These all are related to IMEI; a unique number used by GSM networks to identify and trace a mobile phone.
    EFS may contain hardware info like configuration files, WiFi/BlueTooth MAC’s, IMEI (or ESN for a CDMA based device) etc.
    EFS and MODEMST1 may be a single partition on some phones.
    FSG (FileSystem Golden copy) and BACKUP are backups of MODEMST1 and MODEMST2 respectively. If MODEMST1 or MODEMST2 are erased (by wrong factory flashing say) and phone notices an invalid partition, FSG and BACKUP will be restored.
    MODEMST1 and MODEMST2 also contains modem firmware files.
    PARAM - stores a number of parameters, variables and settings of the hardware. It contains info whether MODEMST partitions are backed up or not. Also debug settings, custom ROMs flash count, current stage boot process etc.

    OEM - like VENDOR, it incorporates OEM (Original Equipment Manufacturer i.e. hardware manufacturer or Mobile Phone brand) small customization (modifications) to original Android (AOSP) during OTA updates such as customized system properties values etc.
    PAD - related to OEM
    OTA, FOTA - OTA updates
    DDR - Double Data Rate RAM
    FSC - Modem FileSystem Cookies
    SSD - Secure Software Download, a memory based file system for secure storage, stores some encrypted RSA keys
    DEVINFO - device information including: is_unlocked (aboot), is_tampered, is_verified, charger_screen_enabled, display_panel, bootloader_version, radio_version etc. Contents of this partition are displayed by "fastboot oem device-info" command in human readable format. Before loading boot.img or recovery.img, bootloader verifies the locked state from this partition.
    CONFIG/FRP/PDB - saves state of Factory Reset Protection (FRP), "Allow bootloader (OEM) unlocking" . (Developer Options), asks already associated account info. This partition is erased/reset if Factory Reset done from Settings.
    DEVCFG - used by TZ for upgrades
    LKSECAPP - "LK (Little Kernel) Security App", related to RPM, TZ online verification / update
    LIMITS - Qualcomm Limits Management Hardware (LMh) driver in SBL writes the data in this partition to use for later reboots
    SYSCFG - Qualcomm CPR (Core Power Reduction) Regulator for better performance and power saving of application processor by voltage control
    DIP, MDTP - boot verification, use Qualcomm SafeSwitch technology to lock and track theft phones
    CMNLIB, KEYMASTER - verified boot
    SEC - contains fuse settings, mainly for secure boot (signing bootloaders for chain of trust) and oem setting
    KEYSTORE - related to /data Full Disc Encryption (FDE)
    MCFG - (Modem Configuration Framework) - on dual SIM devices, loads MBN (modem binary) files depending on SIM/carrier
    SPLASH - splash image or boot logo which appears when device boots (at ABOOT stage).
    CHGLOGO - charging screen that appears when charger is connected to powered off device.
    MSADP, APDP, DPO - related to debug policies
    GROW - empty for future expansion

    7. FILESYSTEMS
    Supported filesystems by your kernel can be viwewd by:
    Code:
    ~# cat /proc/filesystems

    Partitions with Mountable Filesystems
    Following partitions are mounted during boot process:
    system, vendor, odm, userdata (mounted at /data), cache, cust, persist (mounted at /persist or /mnt/vendor/persist), modem (mounted at /firmware or /vendor/firmware_mnt), dsp (mounted at /dsp or /vendor/dsp)
    Modem is formatted as vfat while all others are usually ext4 or f2fs on newer devices.
    All of these are listed in /fstab.* file which is processes by init. Starting with Android 8.0 (Treble release), fstab.* is moved to /vendor/etc/ and system, vendor and odm entries are included in dtb.

    Other partitions don't contain a mountable filesystem. However, we may try to get an idea of the contents by reading smaller partitions e.g.:
    Code:
    ~# cat /dev/block/bootdevice/by-name/config | strings
    ~# cat /dev/block/bootdevice/by-name/misc | strings

    Pseudo / Virtual / in-Memory Filesystems (Kernel space)
    These filesystems don't rely on a physical persistent storage but just live in RAM, to provide kernel services interfaces in user space.
    rootfs (/) - mounted by kernel before calling init. More details here
    sysfs (/sys) - information related to devices, populated by kernel
    devpts (/dev/pts) - character device files representing slave side of pseudo terminal pairs
    proc (/proc) - information related to all processes, updated as processes are started / killed
    tmpfs (/dev) - all device nodes updated from sysfs, accessible from user space
    configfs (/config) - intergrated with userspace sdcardfs, controls apps permissions to directories on internal/external sdcard by VOLume Daeomon, a replacement of fusefs
    pstore (/sys/fs/pstore) - persistent storage, a replacement of /proc/last_kmsg, saves last kernel console messages on panic / crashes / sudden reboots, solution to volatile nature of pseudo filesystems
    cgroup - cgroups manage hardware resources allocation to processes as per load
    selinuxfs (/sys/fs/selinux) - implementation of Security-Enahanced Linux, a mandatory access controls (MAC) to manage file permissions, better than traditional Discretionary Access Control (DAC) mechanism (Read-Write-eXecute) of Linux
    debugfs (/sys/kernel/debug) - to monitor and debug kernel space implementations from user space
    tracefs (/sys/kernel/debug/tracing) - debugfs with better security
    functionfs (/dev/usb-ffs/adb) - integrated with configfs, manages USB gadgets, ADB is implemented through functionfs on Android

    FILESYSTEM TREE MOUNTED BY INIT: ANDROID vs. LINUX

    8. Factory Firmware and Flashable ROMs:

    When you flash a custom ROM, that ROM typically includes a kernel and an OS. That means the /boot and /system partitions will be modified at a minimum. Some ROMs require a clean install, so a format of the /data and /cache partitions is sometimes built into the .zip that you flash. This is essentially doing a Factory Reset.
    Read here to know more about flashing partitions.
    Factory Firmware contains original iamge files of almsot all important partitions. It's provided by OEM's, usually as a package which also incude a flasher software for PC. Or a general flasher software may be uses such as QFIL.

    ROM Development
    A ROM developer downloads AOSP source code from Google while device tree, driver binaries and kernel source code is provided by (ODM's through) OEM's, if they are generous enough. OEM's manufacture and sell devices themselves while ODM's sell to white-labelers who brand them under their own names. Original Android kernel tree is provided by Google which in turn is taken from Linux and then modified by Google for Android-specific needs.

    RELATED:
    2
    First off, don't need be like your never be a dev, lol you never know. Secondly it's a good share. Appreciated
    2
    Well done

    To the one person that started this thread....

    Hats off to u. U have explained a lot that took me 20yrs in the IT field to learn. Basically a Android phone is just a handheld computer. Specifically designed to a carriers wants. That is why u have the same phone but different setups. The company's checks verify if things are what they're supposed to be mainly partitions and sizes of each. If they don't match it errors out causing chaos to users. Lol
    Such as Sprint partitions are different from tmo and att etc. Understanding all of that could take years but knowing the basics would help anyone to understand variants thus becoming simplified and less troubleshooting required.

    In my case, my understanding of everything covered but in the PC world helped me tremendously associate its equivalent counterpart in phones. Thus everything they say that can't be done actually can. It's all just a matter of finding the commands or for the lazy the tools that would do what they want.

    Think of it as building a pc. You put h/w together but it's still nothing until you configure your CMOS (Bootloader). Once hardware working then you have hard drive (internal Storage) still useless until you format. You make one single partion (c: drive) or several of different sizes catered to ur preference (c: is d: data x:restore etc. or counterpart boot.img userdata.img recovery.img)

    I hope u continue on with ur knowledge seeking but moreso you pass it on. Again congratulations and wish u the best.
    2
    @Alicias , please do not quote the entire OP as it clutters the thread unnecessarily. thanks

    ---------- Post added at 11:38 PM ---------- Previous post was at 11:03 PM ----------

    someone please correct me if i am wrong but i believe the usb would be in /dev/sdc8 (/misc). simcard ? i have no idea. good luck.
    2
    Very nice compilation for a noob as you stated.
    Written by noob, read by noob, and understood by noob.
    Nice Work.