I am working with an embedded Linux system not related to any standard Linux distro like ubuntu or centos. The system utilizes many standard FOSS packages like systemd, busybox, shadow, etc.. The user accounts on the system are prompted to change the default login password upon the first login.
When the system does an upgrade of the file system, some information needs to be preserved. When I update the system, I want to preserve the login passwords, which is not a problem. But once the system is upgraded, the system determines the user accounts are the 'first login' and prompts the user to change the password. I want the system to retain the knowledge that the password has already been changed.
Is there a Linux configuration file with shadow or useradd that I need to retain and move during system upgrades to let the system know that this user has already logged in and reset the password?
Any info or feedback would be helpful. Cheers.