Then do a backup of your recovery partition first, from the normal mode, as root, and replace it with a custom one:
dd if=/dev/block/bootdevice/by-name/recovery of=/sdcard/recovery-backup.img bs=2048
dd if=/sdcard/recovery.img of=/dev/block/bootdevice/by-name/recovery
Now you can proceed with the flashing of dumpall.zip. Installation is quite simple:
- Put the zip into the SD card;
- reboot the phone in Recovery Mode: Power+On or from adb "adb reboot recovery";
- Mount /system;
- Apply update from SD Card;
- Select the .zip file;
- Wait about five minutes.....
- Reboot system now.
All the files will be saved into a DUMPS folder on the SDcard. Them are .img files mountable as removable volumes.
The system.img file is the /system partition. More often, in case of problems, you need only flashing this partition. Remember that at the first boot the recovery partition will be reinstalled by an internal script of the system partition.