How to change raspbian / Raspberry pi OS user name

Change user name

https://raspberrytips.com/change-raspberry-pi-username/

https://www.scaler.com/topics/how-to-change-username-in-linux/

allow ssh login for root via ssh

sudo vi /etc/ssh/sshd_config

#PermitRootLogin prohibit-password

PermitRootLogin yes

set password on root

passwd root 

logout of all instances of old user

ssh to host as root

change user name

usermod -l newusername oldusername 

change user directory

usermod -d /home/new_username -m new_username

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change user name and home directory of linux user

Rename the user on linux.

This changes the login id and the home directory name.  It will not change any of the info in possible config files for shortcuts and packages which were embedded while configuring tools or programs on the account.

Things may have to be edited and replaced as needed manually.

https://websistent.com/change-home-directory-in-linux/

Change the home directory using usermod

This method is for command line warriors. Before you use the usermod command the new home directory should be created, ownership should be assigned to the new user and the folder should be chmoded correctly so that no one else can access it. Run the following commands to do it.
mkdir /home/new_home_directory
chown username:username /home/new_home_directory
chmod 700 /home/new_home_directory
usermod --home /home/new_home_directory username

Change the home directory by editing /etc/passwd

Alternatively you can also edit the /etc/passwd to change the home directory. But you should be careful not to edit anything else. Before editing this file it is always better to create the new home directory and assign proper permissions and ownership to it. Execute the following commands.
mkdir /home/new_home_directory
chown username:username /home/new_home_directory
chmod 700 /home/new_home_directory

Open the /etc/passwd file using a text editor and locate the line containing the required username it should look something like this
username:x:500:500::/home/username:/bin/bash

change it to
username:x:500:500::/home/new_home_directory:/bin/bash

Save the file.
Finally copy all the old content to the new home directory
cp -f /home/username/* /home/new_home_dir/

another link
https://askubuntu.com/questions/558669/renaming-user-name

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