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I recently installed Ubuntu 20.04 on my laptop, single OS only, with full-disk encryption using the standard configuration. When booting, it takes 18-19 seconds from pushing the power key to get to the disk decryption passphrase prompt; after I enter the passphrase, it boots to the GUI quite quickly. How can I reduce the time it takes to get to the passphrase prompt?

There are lots of boot time threads out there, but they all seem to focus on one of two scenarios that do not apply in this case: (1) reducing GRUB time in a multi-OS environment, or (2) reducing time by uninstalling SNAPs, tweaking userspace parameters, etc.

The approximate times are as follows:

  1. 0 sec: Press power key
  2. 0-1 sec: Black screen
  3. 1-5 sec: Manufacturer splash with BIOS prompt
  4. 5 sec: GRUB beep
  5. 5-19 sec: Black screen
  6. 19-21 sec: Manufacturer splash
  7. 21 sec: Disk decryption prompt

My grub configuration is as follows:

GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""

Thanks in advance.

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Delay at #5 above includes GRUB_TIMEOUT of 10 sec, even though GRUB_TIMEOUT is set to 0 in /etc/default/grub. This behavior has been documented here and in a number of other threads. Problem was fixed for me by setting GRUB_TIMEOUT to 1 in /etc/default/grub, then running sudo update-grub. This reduces the delay from GRUB start to disk decryption prompt from ~16 sec to ~7 sec.

Further reduction in boot time would probably require tinkering with BIOS settings, kernel module loading, etc. But I'm happy for now.

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