Please notice this setting should be used only for personal or lab environments where physical access is controlled, as it does not provide strong security and is not recommended for production systems.

#Install btop

sudo apt install -y btop

#To create a restricted user account for running btop. Use a restricted shell like rbash to limit capabilities and prevent access to sensitive system functions. The account should not have a password and should be locked to prevent direct login.

sudo useradd -s /bin/rbash -M btopusr

sudo usermod -L btopusr

sudo mkdir -p /home/btopusr/{.config/btop}

#To create a .profile script in the user's home directory to automatically start btop, select and copy all the lines below to EOF, paste them in terminal and press Enter.
sudo tee /home/btopusr/.profile > /dev/null << 'EOF'
btop --tty_off --low-color
exit
EOF

# Change /home/btopusr/ folder ownership.

sudo chown -R btopusr /home/btopusr/

# Edit tty1 service.

sudo nano /etc/inittab

# Find the next line, # comment it and insert new line next to it, it will look as follows.
#1:2345:respawn:/sbin/getty --noclear 38400 tty1
1:2345:respawn:/sbin/agetty --autologin btopusr 38400 tty1

# Reboot to apply changes.

sudo reboot

After rebooting, the console will display btop instead of the login prompt. Pressing Ctrl+Alt+F2 through F6 will provide access to standard login prompts on other virtual terminals, preserving access for administrative tasks.

# To revert it then just change /etc/inittab to its original setting for the line and comment the one that you added.
1:2345:respawn:/sbin/getty --noclear 38400 tty1
#1:2345:respawn:/sbin/agetty --autologin btopusr 38400 tty1

Tested on Devuan 6 (Excalibur) but it should work the same with previous version or any other system using SysVinit or adapt it accordingly for OpenRC.