How to add debug messages to the boot process in Red Hat Enterprise Linux

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise MRG 1
  • Red Hat Enterprise MRG 2

Issue

  • How to make more verbose booting in Red Hat Enterprise Linux

Resolution

  • Remove the rhgb and the quiet kernel command-line parameters, either by editing the '/boot/grub/grub.conf' file or by using the grub editing mode during boot. Replace these parameters with verbose and debug. This change is generally sufficient to provide as much data as is needed to debug a boot failure.

  • The option rhgb is used for graphical boot-up and the quiet option eliminates most of the boot messages.

  • Additional parameters can be added to produce more verbose logging, here are two examples:

 acpi_dbg_layer=65535 acpi_dbg_level=65535 apic=debug debug_locks_verbose=1 initcall_debug loglevel=7 debug log_buf_len=10M

debug ignore_loglevel log_buf_len=10M print_fatal_signals=1 LOGLEVEL=8 earlyprintk=vga,keep sched_debug initcall_debug

  • Additionally, udev can be in debug mode. Edit the '/etc/udev/udev.conf' file and edit udev_log="err" with udev_log="debug". Also SCSI logging level can be increased for further verbose booting. For that, open the '/etc/sysctl.conf' file and add the line dev.scsi.logging_level=10 and save it. After the change, run the command 'sysctl -p'. Applying these tweaks will make the screen flooded with lots of text, so test before this is put in production.

  • If the messages get removed from the screen too quickly, the file '/var/log/boot.log' may contain the startup messages (if the system boots far enough for the filesystem to be properly mounted).

  • Additional information can be found in What to do if a server fails to boot?

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