How can I delay display-manager.service from starting until after my systemd unit's script has exited?

Question

I'm writing a cloud sync script for Ubuntu 18+ that makes sure some critical files are pulled from the remote as part of the boot process. I'd like it to run after the Plymouth splash screen, but before the user login screen (either with or without a graphical environment).

Delaying login until the script has exited is imperative for this application, because I need to print a message to the console and wait for the user to press a key to acknowledge before they can log in; but I can't seem to get the systemd service unit right.

The example below works for non-graphical environments (systemd default.target = multi-user.target) but not for graphical ones (default.target = graphical.target). What am I missing?

[Unit]
Requires=network-online.target
After=network-online.target plymouth-quit-wait.service
Before=getty@tty1.service

[Service]
Type=oneshot
StandardInput=tty
StandardOutput=tty
StandardError=tty
TTYPath=/dev/tty1
ExecStart=/home/user/myscript.sh

[Install]
WantedBy=multi-user.target

Answer 1

The correct order seems to be after plymouth-quit.service, but before display-manager.service, which is the last unit started before plymouth-quit-wait.service. ie, if enabled, the display manager is started before the splash screen goes away.

So, to overcome plymouth without adding overrides to the display manager service, the workaround is to run the new service on tty2 and switch the virtual terminal to tty2 in the script.

[Unit]
Requires=network-online.target
After=network-online.target plymouth-quit.service
Before=display-manager.service

[Service]
Type=oneshot
StandardInput=tty
StandardOutput=tty
StandardError=tty
TTYPath=/dev/tty2
TTYReset=yes
TTYVHangup=yes
ExecStart=/path/to/script.sh

[Install]
WantedBy=multi-user.target

#!/bin/bash

# Change the virtual terminal to tty2
# so user can interact with the script and see its output
chvt 2

# do stuff
echo "Hello, world!"

# Change back to tty1
# so user is shown console login,
# or sent to wherever the display manager decides
chvt 1

This works, but it's not very clean without adding extra logic to the script or writing a wrapper. If I run it anywhere other than from tty1, for example (like a desktop running on tty7), or if tty2 is already occupied.

This should be okay since my script should only be run at boot, but if there is a pure systemd solution that would allow me to just keep everything on tty1 the entire time when default.target is either multi-users.target or graphical.target, I would love to hear about it.