On the first boot of a fresh DietPi install. The systemd services are launched in the following order:

0. DietPi-FS_partition_resize: Inflate root partition and file system to 100% of available disk space
1. DietPi-RAMlog: Mount tmpfs on /var/log and copy empty log files from disk
2. 1. DietPi-PreBoot: Detect SBC model and apply CPU governor settings
   2. DietPi-FirstBoot: Apply AUTO_INSTALL settings from dietpi.txt
3. DietPi-PostBoot: Print login banner

Then, when you login /etc/bashrc.d/dietpi.bash is executed and loads /boot/dietpi/dietpi-login:

0. Load DietPi-Globals to shell session
1. Print DietPi-Banner and lincense agreement prompt
2. DietPi-Update
3. DietPI-Software: Further firstrun setup prompts and steps are applied

The following services are launched in this order:

1. DietPi-RAMlog: Mount tmpfs on /var/log and copy empty log files from disk
2. DietPi-PreBoot: Detect SBC model and apply CPU governor settings
3. DietPi-PostBoot: Check for DietPi updates, start software services, run custom user scripts and print login banner

Then, when you login /etc/bashrc.d/dietpi.bash is executed and loads /boot/dietpi/dietpi-login:

0. Load DietPi-Globals to shell session
1. Print DietPi-Banner and in case start DietPi-Autostart choices