How to debug Dracut problems

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Foreword

If you are experiencing a problem with system initialization due to Dracut, please see the common bugs document before filing a bug. Some easy configuration tweaks that fix a wide range of issues may be listed there. If the problem you are seeing is not listed there or none of the workarounds seem to help, please consider filing a bug to help us make Fedora run better on your hardware.

Be prepared to include some information (logs) about your system as well. These should be complete (no snippets please), not in an archive, uncompressed, with MIME type set as text/plain.

Contents

Identifying your problem area

Note.png
FIXME
provide guidance on what dracut bugs look like. How to tell if this is related to dracut, or just a kernel problem?

Information to include in your report

All bug reports

In all cases, the following should be mentioned and attached to your bug report:

  • The exact kernel command-line used. Typically from the bootloader configuration file (e.g. /etc/grub.conf) or from /proc/cmdline
  • A copy of your disk partition information from /etc/fstab
  • A device listing from device-mapper. This can be obtained by running the command dmsetup ls --tree
  • A list of block device attributes including vol_id compatible mode. This can be obtained by running the commands blkid and blkid -o udev
  • Turn on dracut debugging (see the 'debugging dracut' section), and attach all relevant information from the boot log. This can be obtained by running the command dmesg|grep dracut.
  • If you use a dracut configuration file, please include /etc/dracut.conf

Software RAID related problems

As well as the information from the 'all bug reports' section, include the following information:

  • If using software RAID disk partitions, please include the output of /proc/mdstat

Debugging dracut

Configure a serial console

Successfully debugging dracut will require some form of console logging during the system boot. This section documents configuring a serial console connection to capture boot messages.

  1. First, enable serial console output for both the kernel and the bootloader.
    • Open the file /etc/grub.conf for editing. Below the line timeout=5, add the following:
      serial --unit=0 --speed=9600
      
      terminal --timeout=5 serial console
    • Also in /etc/grub.conf, add the following boot arguemnts to the kernel line:
      console=tty0 console=ttyS0,9600
    • When finished, the /etc/grub.conf file should look similar to the example below.
      default=0
      timeout=5
      serial --unit=0 --speed=9600
      terminal --timeout=5 serial console
      title Fedora (2.6.29.5-191.fc11.x86_64)
      root (hd0,0)
      kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 console=ttyS0,9600
      initrd /dracut-2.6.29.5-191.fc11.x86_64.img
    • More detailed information on how to configure the kernel for console output can be found at [1].
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Redirecting non-interactive output
You can redirect all non-interactive output to /dev/kmsg and the kernel will put it out on the console when it reaches the kernel buffer by doing
exec >/dev/kmsg 2>&1 </dev/console

Enable the dracut debug module

To turn on dracut debugging, you must rebuild the dracut initial ramdisk with the appropriate parameter. The following commands demonstrate rebuilding the ramdisk with the debug dracut module enabled.

  1. Create a dracut ramdisk image with debugging enabled
    dracut -a debug /boot/initrd-debug-$(uname -r).img $(uname -r) 
  2. Next, tell your bootloader to use the new dracut ramdisk
    grubby --make-default --title "Debugging dracut" \
    
    --add-kernel /boot/vmlinuz-$(uname -r) \
    --initrd /boot/initrd-debug-$(uname -r).img \
    --copy-default
  3. When ready to debug dracut, reboot the system

Using the shell

Dracut offers a shell for interactive debugging in the event dracut fails to locate your root filesystem. To enable the shell:

  1. Add the boot parameter rdshell to your bootloader configuration file (e.g. /etc/grub.conf
  2. Remove the boot arguments rhgb and quiet

A sample /etc/grub.conf bootloader configuration file is listed below.

default=0
timeout=5
serial --unit=0 --speed=9600
terminal --timeout=5 serial console
title Fedora (2.6.29.5-191.fc11.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 console=ttyS0,9600 rdshell 
        initrd /dracut-2.6.29.5-191.fc11.x86_64.img
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FIXME
Need sample shell commands.

Additional dracut boot parameters

rdshell
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Drop to a shell, if the initramfs fails.
rdinitdebug
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set -x for the dracut shell
rdbreak=[pre-udev|pre-mount|mount|pre-pivot|]
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drop the shell on defined breakpoint
rdudevinfo
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set udev to loglevel info
rdudevdebug
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set udev to loglevel debug
rdnetdebug
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debug network scripts in dracut. Output is written to /tmp/

Creating a dracut.conf

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FIXME
more information on creating a a dracut.conf and when that might be needed