How To - change reset password on RPI

Summary

If you forget your password on your RPI, then you can't login to change it. This gives some steps to be able to do that.

Note: this may work only on Ubuntu 22.04 on an RPI.

Other OS's like Raspbian or other versions of Ubuntu may not work.

Step-by-Step Password Recovery

These steps assume you are doing this on an Ubuntu PC. It should work the same on a macOS or Windows but not tested.

Power off RPI, remove SD card, put it in your PC's card reader (microSD)
On your PC, you should see two mounted disks: "system-boot" and "writable"
open the "writable" one. You should see bin, dev, etc, and others
open "etc"
find the file called "shadow" (no extension)6) copy it (just in case!) to "shadow_orig" since that file has special permissions I had to do this from a terminal (not sure how this works in mac or windows)
```
cd /media/your-id/writable
sudo cp shadow shadow_orig
```
open shadow in an editor. I assume that the editor writes linux/mac compatible line endings. if you're doing this on windows, use notepad++ which should work okay.From the command line in Linux:
```
sudo nano shadow
```
find the userid (near the bottom) in my case it looked like this: your-id:$y$j9T$G355Ljqy.opQ8VJfhxB7E/$Iaznza7ds.lmdiQjfip1Y7J/WSkIcNZPwTcEpFNzSh4:20314:0:99999:7:::
delete from first colon to the 2nd colon. It should look like this afterwards: your-id::20314:0:99999:7::: i.e. the encrypted passwords don't have a ":" in them, so delete only those characters between the two ":"
save the file; eject the sdcard; put it back in the RPI
power on RPI; it should come up okay and you should see the login screen and the user id on the screen
click on the userid and it won't ask for your password, it will just login.
to set the password, I tried using the Ubuntu settings (GUI), that didn't work.This did:
- open a terminal
- enter passwd your-id (i.e. the username you want to change)
- enter the new password twice as requested
- you should see "password updated successfully"
reboot and login this time with the new password to double-check everything is okay

Doesn't work

FYI I tried adding init=/bin/sh to the boot command as recommended by AI Gemini and this video: YouTube video

It did not work.

Note it may be okay with Raspian or older version of Ubuntu. I have not checked it.

The process requires you to have a second computer with an SD card reader to access the card's file system.
Remove the SD card from your Raspberry Pi. Insert it into your computer's card reader.
Locate the cmdline.txt file. Your computer should mount two partitions from the card. The smaller one, often labeled "system-boot", "boot" or "bootfs", is the one you need. Inside this partition, you will find the cmdline.txt file. (Note: there is a config.txt, not that one!)
Edit cmdline.txt. Open the file with a plain text editor. It contains a single long line of text. Go to the very end of the line and add a single space, followed by init=/bin/bash e.g. init=/bin/sh Do not add any new lines or remove anything else.Example cmdline.txt (before): zswap.enabled=1 zswap.zpool=z3fold zswap.compressor=zstd multipath=off dwc_otg.lpm_enable=0 console=tty1 root=LABEL=writable rootfstype=ext4 rootwait fixrtc quiet splashExample cmdline.txt (after): zswap.enabled=1 zswap.zpool=z3fold zswap.compressor=zstd multipath=off dwc_otg.lpm_enable=0 console=tty1 root=LABEL=writable rootfstype=ext4 rootwait fixrtc quiet splash init=/bin/sh
Save the file and eject the SD card. Safely unmount the card from your computer and put it back into the Raspberry Pi.
Boot the Raspberry Pi. The system will boot directly into a root command line shell, bypassing the login prompt. You will not be asked for a password.
Remount the file system. The file system will be mounted as read-only. You must remount it as read-write before you can change the password. Type the following command and press Enter: mount -o remount,rw /
Reset the password. Use the passwd command to set a new password for the desired user. Replace "username" with the user you want to reset (e.g., pi). passwd username You will be prompted to enter a new password twice. The characters will not be displayed as you type.
reboot the system exec /sbin/init check you can log in with the new password.
Revert the changes to cmdline.txt You can do it in RPI: sudo nano /boot/firmware/cmdline.txt remove the init=/bin/bash at the end of the line
reboot reboot -f