mjhjmtu

I installed a minimal ubuntu (xubuntu-core). It works well, but boot is a bit too slow.

Right after I make my choice in grub, the screen turns black and after around 15 seconds I see the kernel boot messages, starting with [ 0.028000]. So what's it doing in between, I I.e. after grub, but before the boot messages. And how can I find out?

I remember in an old installation, grub produced output itself (and maybe even a log file?) is there a way to make grub more verbose?

EDIT: systemd-bootchart tells me that the display manager is up after 8 seconds. However, from the moment i made my choice in grub roughly 25 seconds pass.

The bit I'm choosing in grub is pretty vanilla:

menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-29414df5-b194-46a5-ae12-dac11924ae3c' 
 recordfail
 load_video
 gfxmode $linux_gfx_mode
 insmod gzio
 if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
 insmod part_gpt
 insmod ext2
 if [ x$feature_platform_search_hint = xy ]; then
 search --no-floppy --fs-uuid --set=root 29414df5-b194-46a5-ae12-dac11924ae3c
 else
 search --no-floppy --fs-uuid --set=root 29414df5-b194-46a5-ae12-dac11924ae3c
 fi
 linux /boot/vmlinuz-4.18.0-15-generic root=UUID=29414df5-b194-46a5-ae12-dac11924ae3c ro 
 initrd /boot/initrd.img-4.18.0-15-generic

The kernel is setting up all kinds of stuff (CPUs, memory, other low-level platform components such as interrupt controllers) in the early parts of the boot and the relevant messages are being recorded all the time. The timestamps will be zero on all the messages up to the point where a clocksource is initialized. Thus even if there's a lengthy delay at some point during the early boot, you won't see it from the timestamps. Tools like systemd-bootchart just visualize the timestamp data, so they won't help here either.

You need to take a close look at the dmesg log from the early stages to see if there's anything going wrong. Unless there's a misbehaving platform component, broken interrupt delivery or something, the delays could perhaps come from steps like gathering entropy for KASLR. You can try disabling that using the nokaslr boot option and see if it helps.

Run dmesg? Another possibility to debug boot times is systemd-bootchart (or bootchart2), a nice tool that visualizes the boot process as SVG when init=/lib/systemd/systemd-bootchart is passed to the kernel.