I'm running grub2 under my 4.15.0-30-generic x86_64 linux system.

Every time I boot and select this system's entry in the grub menu (or any other system's entry), a screen or two of logged bootup messages zip by, and then the screen goes blank after about 1 second, and the boot sequence is then permanently hung.

The only way I can successfully boot is as follows:

  1. Restart my system
  2. Select the system's (recovery mode) entry in grub's menu.
  3. When the recovery menu comes up, select resume.

During this recovery-based boot sequence, I can see lots of startup messages before and after the recovery screen. The console never goes blank, and the boot always succeeds.

Because the failed boot's log data scrolls by so quickly, I cannot read it before it disappears when the screen goes blank. And since I can only get into my system via that subsequent recovery-based reboot, the previous boot's dmesg entries are gone by the time I can log in. So I don't know how to diagnose this problem.

The following are the contents of my /etc/default/grub file ...

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 4.15.0-30-generic (recovery mode)"
GRUB_DISTRIBUTOR="`lsb_release -i -s 2> /dev/null || echo Debian`"

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)

# Uncomment to disable graphical terminal (grub-pc only)

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux

# Uncomment to disable generation of recovery mode menu entries

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"


Thank you for any insights that anyone can offer.

  • When the system becomes permanently hung, does pressing CTRL-ALT-DEL makes it shutdown and restart? (Note that you may have to wait 1-2 minutes after pressing the keys and the actual restart, but usually there is immediate disk activity when you press that keys combination, meaning the keypress actually triggered a shutdown). – Pablo Aug 20 '18 at 1:55

I figured how to fix my boot problem, based upon this post ... Why is my machine not showing anything when booting?

By default, nomodeset was used for the recovery menu entries, but not the non-recoveries. Adding nomodeset to the non-recovery boot entries fixes the problem with my boot sequence hanging ...


However, I'd still like to know how to debug a boot sequence that hangs with a blank screen. Is there any way to cause grub's log messages to go to a file that can be viewed in a subsequent boot session, so I could review them to see what might have caused the boot problems?

Any thoughts?

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