Changing GRUB_TIMEOUT value doesn’t seem to work

This could be an issue connected to GRUB_RECORDFAIL_TIMEOUT. According to the official Ubuntu documentation—which is still relevant to Lubuntu—it says:

If the last boot failed or after a boot into Recovery Mode the menu will be displayed until the user makes a selection.

To change this behaviour, edit /etc/default/grub and add the variable GRUB_RECORDFAIL_TIMEOUT. Set the value similar to setting for GRUB_TIMEOUT.

1. For -1, there will be no countdown and thus the menu will display.
2. For 0, menu will not display even for a failed startup.
3. For >=1, menu will display for the specified number of seconds.

Run update-grub after the change have been made.

It could be that your setup is somehow just powering down and/or rebooting Lubuntu in a way that makes it feel that the last boot failed—or the system crashed—thus it’s going to look for the GRUB_RECORDFAIL_TIMEOUT value and use it’s default value if it’s not set elsewhere.

Regardless, here is how I tweak that GRUB_RECORDFAIL_TIMEOUT value.

First, open up /etc/default/grub using nano—or you can use whatever text editor you like—like this:

sudo nano /etc/default/grub

Then I set GRUB_TIMEOUT and then GRUB_RECORDFAIL_TIMEOUT like this:

GRUB_TIMEOUT=0
GRUB_RECORDFAIL_TIMEOUT=$GRUB_TIMEOUT

Note that I am setting GRUB_RECORDFAIL_TIMEOUT with a variable reference to $GRUB_TIMEOUT instead of setting a new number; feel free to change that to a real number if you need different timeout values.

Then I update GRUB and all should be good:

sudo update-grub2