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I was currently learning to create plymouth themes/scripts from this link while following the guide i came across the Plymouth.SetDisplayPasswordFunction area, and after quite an amount of searching on the internet i got lots of information on creating password dialogs in plymouth themes.

I don't understand what is a password dialog doing at such an early phase of booting.I assume that it should show when the GDM has started and plymouth has exited.

I am totally confused, please someone explain me what is it in details and what does it do..

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Certain cases of disk encryption require you to enter a passphrase during boot to unlock the root partition, else the system can't continue booting, because it can't get its data from disk.

Only the boot partition won't be encrypted (or is unlocked by GRUB), so the kernel and the initramfs can still be loaded. But that alone makes a very poor experience, with only BusyBox as a shell and no files to work with.

Without a Plymouth splash, the password prompt will simply be written on the TTY, e.g. something like this:

enter image description here

With Plymouth, you can have a password prompt drawn over the boot splash. Here are some examples:

enter image description here enter image description here

(All images taken from Google Image Search)

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  • so if i create a custom plymouth script for my os, is it necessary to include such an password dialog or are there other workarounds.
    – Soumya Kanti Sar
    Commented Jan 25, 2016 at 1:16
  • AFAIK it is not necessary, but I don't know what happens if there is no dialog implemented.
    – s3lph
    Commented Jan 25, 2016 at 10:29
  • If you don't implement a dialog for password/question prompt, the splash screen will wait for input without showing user anything. User can still input their response, and when they hit enter it'll be passed to the underlying component. Without a prompt, though, user will have trouble knowing what & when to input.
    – starleaf1
    Commented Aug 30, 2017 at 14:58

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