Installing Marshmallow

If anything is unclear, check if Installing LegacyXperia for Dummies provides more detail.
If everything is unclear, don't install LX13 (Marshmallow). Wait a week or two until it has been tested by experienced users.

Download

• LX13 ROM
• Mardon's LX13 GAPPS, Mini version, make sure you choose for the right screen (HDPI / hi-res screen vs. MDPI / low-res screen):
  http://forum.xda-developers.com/android/apps-games/hdpi-google-apps-6-0-1-upd-20160121-t3307611

Partition your SD card with exactly 1 partition

ALL DATA WILL BE LOST. Backup anything you need.
Basically, you need a normal SD card; if you repartitioned for Lollipop, you must revert that.

• You MUST have exactly 1 partition on the card. The recovery cannot change the partition layout.
• The partition type must be "primary" and "not active".
• speed matters, this will hold the /data partition. UHS-1 / Class 10 strongly recommended. Note that Class10 cards can still differ a lot; the orange Samsung EVO cards seem to be good for this use case.
  See Tuning SD Card Speed
• on Windows, use MiniTool partition wizard and an SD card reader (easy). On Linux, use gparted, or see Partitioning the SD Card using ADB (not easy)
  Note that sometimes Partition Wizard creates a small empty 2nd partition - this could cause problems.

Once you have the 1 partition:

• format to F2FS; or keep unformatted (then it will be formatted to F2FS later; the same should work with FAT32, but not all fat variants like vfat/exfat have been tested)
• alternative: format to ext4 (this is no longer standard and not recommended, but it may be faster for some cards)

Flash LX13 kernel

• follow the usual procedure:

1. make sure you extracted boot.img from the ROM.zip
2. connect phone in fastboot mode
3. fastboot flash boot boot.img
4. fastboot reboot
5. enter Recovery

Wipe SD card

All data on the SD card will be deleted. Wiping is needed only the first time you install LX13, or when you have problems.

1. Boot to Recovery
2. factory reset > full factory reset
3. Wipe cache
4. advanced > wipe system partition

NOTE: this will format the card to F2FS if necessary, and create /data and /data/media on it.
/data/media is used to emulate an SD card (Android acts like its content is on a separate SD card, where photos are stored for example). You cannot access /data/media via the plain file system with a card reader.

Flash the images using sideload

NOTE: You must have the latest ADB version 1.0.32. Check with 'adb version'.
With an older version you will get "protocol fault (no status)"

1. reboot again to recovery (Note: the "reboot recovery" option does not work. Do a normal reboot and press the recovery key instead)
2. connect USB to PC
3. Select Apply update > Apply from ADB
4. Sideload LX13 rom (takes 10 minutes). Example:
   adb sideload cm-13.0-20160224-UNOFFICIAL-LegacyXperia-urushi.zip
5. again, Select Apply update > Apply from ADB
6. Sideload GAPPS (this is optional, but you most likely want it)
7. Sideload anything else you want (keyboard etc.)

NOTE: cm13 includes toybox instead of busybox (a tool to execute scripts). As a result, assume that images for older cm versions will not work.

NOTE: install GAPPS before you boot for the first time. (Only before the first boot, installers get special privileges).

NOTE: if you have installed LX13 before, and you enabled ADB debugging and verified your PC, you can also move the images to the phone using ADB, and flash the images from the Recovery. It's easier to just use sideload.

Reboot

• the first boot will take a while; all apps are compiled.

Enjoy

• Instructions unclear, ca3%@//____
• this is 2016 and that little bugger runs cutting edge Android :)

Random Notes

• In Recovery mode, initially any adb command other than sideload results in "unauthorized". Once you have booted and authorized the PC for adb access, Recovery can read the keys from /data.
• Speed is similar to Lollipop; except that Lollipop runs the CPU at 1.4GHz and Marshmallow at 1.0GHz. If you want more speed but less battery, use an app like 'No-frills CPU control' to run at 1.4GHz. Don't forget to check 'set at boot' or it will revert to 1.0 at next boot.
  Note that the CPU is designed for 1.4GHz; SonyEricsson chose to underclock to 1.0 to conserve battery.
• Bluetooth works, or it doesn't, or it does when it feels like it; this is a known problem.
• The screen may be a bit dark; some prefer to disable Settings > Display & Lights > Adaptive brightness
• Keyboard swiping ('Gesture Typing') does not work (maybe because of missing dictionary files). Easy workaround is to install Google Keyboard from the Play store.